The use of a Real-Time Displayed Measuring System

for X-rays - an evaluation of personnel doses in an angiography room with a

DoseAware System

MASTER DEGREE THESIS IN RADIATION PHYSICS

Tu Mai

Department of Radiation Physics

University of Gothenburg

Gothenburg, Sweden

January, 2011

Supervisors: Charlotta Lundh & Åke Cederblad

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Abstract

Radiation protection is an important subject that especially concerns the interventional

radiology personnel; their daily job involves exposure of ionizing radiation.

The DoseAware System (Philips, but developed by Unfors Instruments AB, Göteborg,

Sweden) is a real-time displayed measuring system for X-rays that can be used to increase the

staff’s awareness of radiation. The system consists of a number of dosimeters that detects the

radiation; a base station that visualizes dose rates and accumulated doses and stores the dose

information until this is exported to a computer; two software programs that enables analyzis

and compilations of the dose data.

This study concentrates upon radiation protection for the staff in the angiographic room and

the aim was to see if the DoseAware System could change the personnel’s working method

from a radiation protection point of view, and thus lower the staff radiation dose.

In this study, the dose information of the staff in the PCI laboratory in Halmstad Hospital was

analyzed. The staff consisted of 3 cardiologists and 10 nurses with special knowledge in PCI

and they had their dose information collected during 2 months. Personal dosimeters (PDMs)

were given to the staff and in the first month, the dose collection was conducted while they

were working as usual, with the only difference that they were wearing this particular

dosimeter. During the second month, the staff kept wearing their dosimeters and was able to

see their current radiation exposure on a monitor while they were working. The dose

information collected in the first month was then compared to the second, to see whether a

change had occurred.

The results showed a change in dose to the patients. One operator has lowered the median

KAP value per procedure with 24 %, which was statistically significant (p = 0.037). The same

operator has also reduced his median PDM dose per procedure with about 61 % (p = 0.023).

The system has moreover reduced the assisting nurses’ median dose per procedure with 38 %

(p = 0.017).

A decrease in collective doses for all the working categories has been registered in Period II.

The reduction was 35 % for the operators; 37% for the assisting nurses; 13% for the “wait on”

nurses and 17% for the patient responsible nurses. The estimated eye doses showed that

neither one of the staff members have received an eye dose near the dose limit. The highest

estimated eye dose was 3.6 mSv/year.

As a result from the focus group interviews, the personnel thought that the DoseAware

System has improved their radiation awareness. The system has helped the staff to better use

the radiation protection screens, and guided them to better working positions.

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Sammanfattning

Strålskydd är en viktig aspekt som speciellt berör personalen inom interventionsradiologin då

deras dagliga arbete involverar exponering för joniserande strålning. Detta arbete inriktar sig

på strålskydd för personalen inom angiografiverksamheten och syftet var att ta reda på om ett

realtidsvisande mätsystem för röntgenstrålning kunde förändra personalens arbetssätt ur just

strålskyddssynpunkt, och således sänka personalens stråldoser.

DoseAware systemet (Philips, men utvecklad av Unfors Instruments AB, Göteborg, Sverige)

kan användas för att öka personalens medvetenhet om strålning. Systemet består av ett antal

dosimetrar (PDM:er) som detekterar strålningen; en basstation som visualiserar dosrater och

ackumulerad dos och som fungerar som länken mellan dosimetrarna och en dator;

datorprogram som möjliggör analyser och jämförelser av insamlade dosinformation.

I denna studie analyserades dosinformationen hos en personalgrupp på PCI laboratoriet i

Länssjukhuset Halmstad, där gruppen bestod av tre kardiologer och tio sjuksköterskor som

hade specialkunskap om PCI. Personalen fick personliga dosimetrar och under två månader

gjordes insamlingen av deras dosinformation. Under första månaden gjordes insamling medan

personalen arbetade som vanligt, med enda skillnaden att de bar denna extra dosimeter. Under

andra månaden fortsatte personalen att bära sina dosimetrar men fick nu möjligheten att se

sina aktuella dosrater på en monitor (basstationen) medan de arbetade. Dosinformation

insamlad under den första månaden jämfördes sedan med den andra för att se om en

förändring hade inträffat.

Resultaten visade en förändring i dos till patienterna. En operatör hade sänkt median KAP-

värdet per procedur med 24 %, vilket var statistiskt signifikant (p = 0,037). Samma operatör

hade även reducerat sin median PDM-dos per procedur med 61 % (p = 0,023). Användandet

av systemet har även lett till en minskning av assisterande sjuksköterskornas mediandoser per

procedur med 38 % (p = 0,017).

En minskning i kollektivdos för alla yrkeskategorier har inträffat i period II. Minskningen var

35 % för operatörerna; 37 % för assisterande sjuksköterskorna; 13 % för ”pass-opp”

sjuksköterskorna och 17 % för de patientansvariga sjuksköterskorna. De uppskattade

ögondoserna visade att ingen i personalgruppen ska ha erhållit en ögondos nära dosgränsen,

utan den högsta ögondosen uppskattades till 3,6 mSv/år.

I fokusgruppsintervjuerna framgick det att personalen trodde att DoseAware systemet har ökat

deras medvetenhet om strålning. Systemet hade även hjälpt personalen att bättre använda

strålskyddsskärmar, och guidat dem till arbetspositioner där de är bättre skyddade från

strålning.

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Table of Contents

1 Introduction ................................................................................................... 6

1.1 Background ...........................................................................................................................6

1.2 Dose limits and radiation protection ......................................................................................7

1.3 Real time visualization of dose rate .......................................................................................9

2 Aims ............................................................................................................... 9

3 Materials and Methods .................................................................................. 9

3.1 Interventional cardiology department in Halmstad Hospital ..................................................9

3.2 The measurement set up .......................................................................................................9

3.3 The data collection periods .................................................................................................. 13

3.4 Data analyzis ....................................................................................................................... 14

3.5 Focus group interviews ........................................................................................................ 17

4 Results .......................................................................................................... 17

4.1 Kerma Area Product (KAP) and reference PDM .................................................................... 19

4.2 Patient doses ....................................................................................................................... 19

4.3 Personnel doses .................................................................................................................. 21

4.4 Focus group interviews ........................................................................................................ 25

5 Discussion .................................................................................................... 26

5.1 Kerma Area Product (KAP) and reference PDM .................................................................... 26

5.2 Patient doses ....................................................................................................................... 27

5.3 Personnel doses .................................................................................................................. 28

6 Conclusions .................................................................................................. 30

Acknowledgements ........................................................................................ 32

References....................................................................................................... 33

Appendix 1 ...................................................................................................... 34

Appendix 2 ...................................................................................................... 34

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1 Introduction

Questions concerning radiation protection are always topical and since the imaging systems

that are used in health care are being improved, there are also higher demands on radiation

protection. This especially concerns the interventional radiology personnel where the

collective dose for the staff in interventional radiography stands for more than 90 % of the

collective dose for all personnel in radiology work.

In this study the staff in a PCI laboratory at Halmstad Hospital has been using a real-time

displayed measuring system for X-rays. The staff’s dose information was collected during two

periods to see if there was a change in doses before, and after that they had the possibility to

see their current dose exposure. The total number of procedures that were analyzed during

these two periods was 153. The aim was to see if such a system could help them to be more

aware of the radiation protection, and thus lead to a decrease in their personal doses.

1.1 Background

In the radiology world, intervention means using X-ray imaging to, as an example, receive a

visual guidance of the coronary vessels which often replaces more complicated surgical

procedures. Coronary angiography is a common cardiology procedure and is an X-ray

examination of the blood vessels or chambers of the heart. Another common procedure is

percutaneous coronary intervention (PCI) and this most commonly involves insertion of

catheters used to widen stenosis in the coronary arteries.

Like many other professions, interventional radiology workers have risks in their jobs. For

these workers, good radiation protection can prevent the risk of acute effects like cataract and

skin injuries (mainly on the hands). Optimized radiation protection is also the best approach to

minimize late radiation effects induced by the radiation, mainly cancer.

The International Commission on Radiological Protection (ICRP) has set a threshold dose for

potential cataract at 4 Gy if the lens of the eye is exposed during a period shorter than 3

months. If the dose is received for a period longer than 3 months, the same potential effect can

be observed at 5.5 Gy. These threshold doses have later on been questioned by ICRP

themselves and the Commission has in later publications pointed out “recent studies have

suggested that the lens of the eye may be more radiosensitive than previously considered” [1].

This has lead to studies that evaluated risk for the personnel of radiation cataract after

occupational exposure in interventional cardiology. One study involved 58 interventional

cardiologists and 52 paramedical personnel (nurses and technicians) and the results showed a

significantly elevated incidence of radiation-associated lens change in the interventional

cardiology workers [2].

Skin injuries are an acute effect that both patients and interventional personnel can be

afflicted with. Skin injuries are occurring in patients as a result of very high radiation doses

during interventional procedures, and operators can receive high doses if their hands are in the

area of the X-ray beam. The severity of this radiation effect increases with increasing dose

and can result in simple erythema to severe burn of the skin. This shows how important good

radiation protection is.

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Sweden is one of many countries that in radiology work, works after the so called

“ALARA”- principle (As Low As Reasonably Achievable) which means optimization of

radiation protection and that all radiation exposure should be kept as low as possible with

regard to social and economical factors. The Swedish Radiation Safety Authority (SSM) has

decided that every work with ionizing radiation regarding medical diagnostics has an

obligation to control the staff’s occupational doses. SSM has investigated the status of

radiation protection regarding the PCI in Swedish hospitals, and suggests that some routines

should be made so that doctors can get feedback in their work. This can be done by analyzing

and making personal compilations of the fluoroscopic time, which can be further used to

identify needs in education. SSM also suggests that the measuring routines of occupational

dose to the staff should be improved by frequent measurement of radiation doses to hands and

to the lens of the eye and moreover, evaluate the registered personal doses. [3] In Swedish

hospitals, the thermoluminescent dosimeter (TLD) is the most common dosimeter used by the

personnel in the radiology area. One disadvantage with this kind of dosimeter is that it does

not immediately show your accumulated dose, the accumulated dose is usually read after one

month of use. SSM has decided that TLDs should be placed inside the lead apron, which can

give an underestimated value of the absorbed dose to parts of the body that is not covered by

the lead apron such as the face (particularly the lens of the eye) and the extremities. After

reading the TLDs, hospitals also have a threshold for reporting doses, which doses below this

are classified as zero. A dose value of 0 mSv only indicates that there is no greater risk in the

way the person is working, and a potential risk of getting 0 mSv month after month is that you

might not get motivated to change your working method to reduce your personal dose. Like a

doctor ironically said:

“Our TLDs always show 0, so I guess there is no radiation?”

1.2 Dose limits and radiation protection

In interventional radiology, and radiology in general, three kinds of radiation are involved.

The primary radiation comes directly from the X-ray tube and the secondary radiation is the

radiation that has been scattered because of the irradiated volume, i.e. the part of the patient

that is irradiated. Since most the scattered radiation will be back scattered, the X-ray tube is

placed under the patient table whenever possible. This type of radiation is the main

contributor to the staff’s personal doses. The transmitted radiation that generates the images

can also cause an increase of personal doses if the hands of the personnel are within the beam

field on the exit side. Some arrangements can be done to minimize the personal doses to the

staff [4]:

Always use lead aprons and thyroid protection. Use protective eyeglasses as often as

possible (especially if you work close to the radiation source, i.e. the patient).

Use radiation protection screens (mobile, suspended from the ceiling or from the table)

whenever possible and suitable.

Try to keep a big distance to the radiation source (the irradiated part of the patient)

whenever possible and suitable.

Avoid making projections with the X-ray tube above the table. At lateral projections,

stand on the same side as the image intensifier or detector.

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Operators (i.e. the cardiologist) can change the settings of the X-ray apparatus to

change the dose (e.g. set the dose setting in low-dose mode when that is suitable). He

or she can also collimate the beam.

This study focuses on the radiation protection of personnel, and the radiation source will refer

to the part of the patient that is irradiated since this is the origin of the secondary radiation that

will contribute to the personal dose of the staff.

SSM has declared dose limits for some different parts of the human body [5]. This is shown in

Table 1.

Table 1. Dose limits for different parts of the body

Unlike imaging with a conventional X-ray tube or with computed tomography (CT), the

personnel in an angiography room do not have the same possibility to leave the examination

room during the radiation exposure. For example, at coronary angiography or PCI, the

operator and the assisting nurse are always present in the room while conducting image series.

An extreme situation is when the patient is having a cardiac arrest during a PCI, and the

operator is forced to continue to irradiate while the other members of the staff are doing

cardiopulmonary resuscitation (CPR). This situation can give very high equivalent doses to

the hands.

Another explanation to high effective personal doses for the staff in the interventional work is

the short distance to the radiation source. The operators often work close to the patient and it

is sometimes not practical to use the protection screens. Protective eyeglasses are a radiation

protection tool that should be used when working close to the radiation source. They are

unfortunately not always worn and especially not during longer procedures where they can

seem to be clunky and uncomfortable.

In PCI the projections are often angled and depending on what angles that are used, these

situations can sometimes give the staff more scattered radiation compared to conventional PA

or AP projections. This is due to the fact that an irradiated volume might seem thicker in some

projection angles. A thicker volume would require higher tube voltage which means higher

KAP and thus would generate more scattered radiation. For example, a small child that is

irradiated generally generates a smaller amount of scatted radiation than an adult. The amount

of scattered radiation also depends on the fluoroscopic time and for some procedures this can

be up to 30 minutes.

Other factors that can affect the staff’s personal doses are the type of the X-ray device,

technical settings (e.g dose settings: low, normal or high), type of procedures and of course,

the skill of the operator which plays a major role.

Organ/part of the body Dose limit

Lens of the eye 150 mSv/year (equivalent dose)

Skin & extremities 500 mSv/year (equivalent dose)

The whole body 50 mSv/year (effective dose) 100 mSv/ 5 years

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1.3 Real time visualization of dose rate Recently, a real time system for visualization of radiation dose rates has been developed

(DoseAware). The DoseAware System has been used in this study to collect the dose

information. The hypothesis is that such a system can make the staff more aware of the

radiation they are being exposed to. One of the expectations about DoseAware is that an

increased awareness will lead to a lowering of the personal dose. As an example, the staff can

be more aware of what positions in the room that has high dose rates and they can therefore

avoid that “hot spot” or try to spend as little time as possible in that position. They can also be

reminded to keep a good distance to the source of radiation (in this case, the part of the patient

that is being irradiated) and use available radiation protection screens and adjust them into a

correct position. When seeing high dose rates, the operators might keep in mind to collimate

the beam, or will not press the exposure button longer than necessary.

2 Aims

The main aim of this project was to see if the system has affected the staff’s personal doses

and if there has been a change of the dose to the patients. We also wanted to investigate if the

real-time visualization of dose rate could lead to a change in the personnel’s radiation

protection awareness, and if visualization was a good educational tool. It was also in our

interest to estimate the effective dose and the equivalent dose to the lens of the eye.

3 Materials and Methods

3.1 Interventional cardiology department in Halmstad Hospital This study was carried out with help from the staff at the PCI laboratory in Halmstad

Hospital. The laboratory has activity Monday to Friday, both planned and emergency cases,

and also has preparedness in the evenings. The staff consisted of 3 cardiologists and 10 nurses

with special knowledge in PCI. During a procedure, a nurse can have one of three “roles”.

The assisting nurse is dressed sterile and works close to the operator at the examination table.

The so-called “wait on”-nurse helps the assisting nurse by handing him or her materials and

has often the possibility to sit outside the room during the majority of a procedure. The

“patient responsible”-nurse watches the patient’s condition, gives medication and documents

the procedure. This nurse often sits behind a radiation protection screen. An overview of the

angiography room can be seen in Figure 1 where the different positions of the staff are

marked in different colors.

3.2 The measurement set up

The X-ray system was a Philips Integris H5000 C angiography system and the collection of

dose information was performed with the DoseAware System (Philips, Holland). The 3

cardiologists and the 10 nurses each received a personal dosimeter (PDM) that was placed

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outside the lead apron. A base station was installed inside the angiography room in a position

that was considered to be best seen from the working positions of the cardiologist and the

assisting nurse. A PDM was attached on the C-arm as a reference PDM. This can be seen in

Figure 2. Another PDM was given the name ”Forehead PDM” and was attached on a

bandeau. The idea with this was to compare the dose values at chest level relative to eye

doses.

Figure 1. A schematic overview of the angiography room. The operator (orange circle) is placed closest to the

patient (the source of radiation). The assisting nurse (purple) is also near the examination table. The "wait-on"

nurse (yellow) is located at a short distance from the examination table but can often sit outside the room, and

the pink circle locates the position of the “patient responsible”, usually behind a radiation protection screen.

The PCI laboratory at Halmstad Hospital has several radiation protection screens. One is

floor-mounted and is placed in front the patient responsible nurse. The table and ceiling

suspended screens are near the examination table and this is shown in Figure 3.

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Figure 2. The positions of the base station (red circle) and the reference PDM (blue circle on the C-arm) inside

the angiography room.

Figure 3. The radiation protection tools that are available in the angiography room. The ceiling suspended

screen is marked with red lines.

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3.2.1 The DoseAware System

The DoseAware System consists of a number of personal dosimeters (PDMs), a base station,

a cradle and two computer programs. Figure 4 illustrates the hardware of the system.

A PDM consists of four semiconductor detectors and gives a Hp(10)-value which is the dose

equivalent at a depth of 10 mm in tissue. The PDM measures dose rate in the range 40 µSv/h–

150 mSv/h with the accuracy of ±10 % and 150 mSv/h – 300 mSv/h with the accuracy of ±20

%. The dose range is 1 µSv-10 Sv. The dose information is sent wirelessly to the base station

near with 1-second delay and the base station can communicate with the PDMs in a range of

10 meters. The base station receives the information that has been sent from the PDMs, and

visualizes dose-rates in shapes of bars for maximum 8 PDMs at the same time. The bars can

have three colors where green bars shows dose-rates ≤ 0,2 mSv/h, orange bars ≤ 2 mSv/h and

red ≤ 20 mSv/h. The base stations second function is to store the received dose information

and work as a link between the PDMs and the computer.

The DoseAware System has two computer programs that can be used for analyzing the dose

information. The DoseView is used when a PDM is placed in a cradle and connected to the

computer. The program shows the dose history of that PDM, and the information can be

shown as a dose graph or as a dose table. The dose history cannot be saved.

In this study, the Dose Manager program has been used for analyzing the dose data. This

program can handle dose history from several PDMs, and the dose history can be shown as a

dose graph or as a dose table. One big advantage is that the history can be saved.

Figure 4. The hardware of the DoseAware System with the base station on the left, a PDM in the middle and a

cradle on the right. (Note that the cradle and the PDM are not in correct size compared to the base station)

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Concerning the suggestions that SSM made for improving the working environment for the

interventional radiology personnel, the DoseAware System can potentially be used to obtain

some improvements:

The software program DoseManager can give a value of the accumulated dose after a

procedure (or any other time-interval) which enables evaluation of personal doses.

DoseManager can also be used for retrospective analysis where one can compare the

dose graphs from two procedures.

The base station gives instant information about the dose rate exposure which can be

considered as feedback on how the staff is acting in the room.

One important thing to remember is that DoseAware dosimeters do not replace the TLD or

other legal dosimeters, and should be more considered as a tool for improving the staff’s

awareness so that they easier can take action and optimize their radiation environment.

3.3 The data collection periods

The dose information from before and after the visualization of the dose rates was analyzed to

see if there was a difference between the two periods. During the first period of the data

collection, 76 procedures (48 coronary angiographies and 28 PCI) were performed. In the

second period 77 procedures (51 coronal angiographies and 26 PCI) were analyzed.

Before the study began, the staff was informed about the purpose with the study, what the

DoseAware System was, how it worked and it was particularly pointed out that the PDM

should be fixed outside the lead apron. The main aim was to compare the dose information

when the staff was working just like they normally would do, with the period when they were

able to see their current dose rate.

Each of the two periods started with a short lesson in radiation protection. Communication

and Learning, the Department of Education, University of Gothenburg, gave advises and

stressed the importance of not adding new information that could influence the staff’s

working behavior once the study had started. To avoid biases from new knowledge, the same

information was given before each study period started.

As a complement to the dose history that can be shown in the DoseManager, the staff was

asked to fill out a protocol after each procedure. In the protocol, information about the type of

procedure, KAP-values, the total fluoroscopic time, were some of the things that were noted.

This protocol can be seen in Appendix 1.

3.3.1 Period I

During the first four weeks of the study, the staff wore the PDMs that were blinded for the

base station, i.e. the staff could not see the dose rate in real time. The radiation doses were

nevertheless registered and this period is also called the “blind phase”. The idea was that they

would be working just like they normally do, with the only difference that they wore a PDM

that registered their dose exposure.

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The operator and the assisting nurse did sometimes wear the “Forehead PDM” during a

procedure. Only operators and nurses that assisted wore this PDM, because these groups were

assumed to get highest dose values, and were therefore more interesting to study. The dose

information from the base station was downloaded once a week and the protocols with

additional information were collected at the same time.

3.3.2 Period II

During additional four weeks, staff’s current rates were displayed on the base station and the

radiation doses were still registered. During this period, the staff continued to fill in the

protocols with additional information. The collection of the protocols and the dose

information in the base station were performed once a week.

3.4 Data analyzis

The analyzis of the dose information from the first and second period was performed in the

same way to get comparable data. The PDM doses of interest were extracted with an

analyzing tool in the DoseManager program. When the dose history was shown as a dose

graph, a selection was made for a time interval of interest (i.e. the time interval for a

procedure) and the “Legend-button” provided a selection summary which gave information

about the total dose, peak dose and the mean dose for all the PDMs of interest. The total dose

for each person involved in a procedure and the dose from the reference PDM was noted and

used for further analyzes and Figure 5 shows a typical dose graph from DoseManager.

Figure 5. A dose graph that can be seen in DoseManager. The continuous line represents the accumulated dose

and can be read on the right axis of the graph. The peaks are the dose-rates at different times and the value can

be read on the left axis.

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3.4.1 Kerma Area Product (KAP) and reference PDM

The X-ray tube has a built-in KAP-meter that provides KAP-values (kerma area product,

Gycm2) after every procedure. The KAP-value is a measurement of the amount of radiation

leaving the X-ray tube. This parameter is very useful since it can be used to correct

differences between procedures and the two periods. This since the KAP-value is, among

other things, dependant on the fluoroscopic time, number of angiography series and the size

of the patient, parameters where differences otherwise can make a comparison difficult.

Doses to the PDM on the C-arm could be used in the same way as KAP. By measuring

scattered radiation in a standardized way you get an indirect measure of dose to the staff if

they would be unshielded from the scattered radiation.

3.4.2 Patient dose

In this study, we wanted to see if there has been a change in effective dose to the patients

between the two periods. We also wanted to find out how the patient skin doses were relative

the action levels.

KAP-values can be used to estimate the effective dose and the skin dose to the patient and the

effective dose E, can be calculated with:

E = EKAP *KAP (1)

where E KAP [mSv/Gycm2] is the transformational factor that has been calculated for different

types of X-ray procedures with regards to the beam geometry and beam quality [6]. For

coronary angiographies, EKAP is set to 0.18 mSv/Gycm2.

A Belgian study has proposed two KAP action levels for skin dose. [7] A first KAP action

level of 125 Gycm2

corresponds to 2 Gy which is the threshold dose for erythema. A KAP

value > 125 Gycm2 would imply an optional radio pathological follow-up depending on the

cardiologist’s decision. The second action level of 250 Gycm2

corresponds to 3 Gy skin dose

and would imply a systematic follow-up.

3.4.3 Personnel dose

We were interested to compare the operator doses per procedure from the two periods. We

also wanted to find out if there has been a change in KAP per procedure and

KAPfluoroscopy/fluoroscopy time per procedure says how good the operator is in collimating the

beam. PDM dose/KAP is interesting since a difference in this quota between the periods

means that the operators have changed their working behavior i.e. better used the radiation

protection screens or kept a bigger distance to the radiation source. The PDM dose per

procedure versus KAP per procedure was plotted to easier see the relationship between these

parameters.

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We wanted to see if the doses to the assisting nurses has changed in Period II. We also wanted

to find out if this change was related to the change in the operator’s working method, i.e. if

the operator had become better in collimating the beam.

Doses to the “wait on” nurses and the patient responsible nurses per procedure were plotted in

bar diagrams that show the accumulated doses and how many procedures the nurses have

been involved in.

3.4.3.1 Collective dose, effective dose and eye dose

The collective PDM dose for the staff was also calculated, and this was done for every

professional category separately. The annual PDM dose for each staff member was estimated

based on this data.

The effective doses were estimated with the Niklason algorithm [8]. If a dosimeter, Ho, was

placed outside the lead apron, the effective dose, E, would thus be:

E = Ho*0.03 (2)

We also wanted to estimate the dose to the lens of the eye. Since the PDMs give Hp(10) –

values and the doses to lenses are measured at 3 mm’s depth, an attenuation correction must

be performed. Equation 2 below shows the formula for the dose at the distance x when the

dose to a point, d, is known:

D(x) = D(d)*

(3)

where

[ is the mass energy-absorption coefficient in water for a photon energy of

30 keV, is the waters density and x [cm] is the distance from d to the point we

want to calculate the dose.

To estimate the dose at 3 mm’s depth, Equation 3 has been used:

D(0.3) = D(PDM thorax)* (4)

Since the operators and the assisting nurses sometimes wore a PDM on the forehead, the

correlation factor Dforehead/ Dthorax was calculated to estimate the dose to the lens of the eye.

The formula for the dose to the lens of the eye was thus:

Deye= D(0.3) * (Dforehead/ Dthorax) (5)

3.4.4 Statistics Student’s t-test was performed to see if there is a statistically significant difference in

collected values between the first period and the second.

Our H0 –hypothesis is that there is no difference in measurement values between the first

period and the second, and the hypothesis will only be rejected if the p-value < 0.05 (5 %).

17

The independent two sample t-test, for unequal sample sizes but equal variances, can be

written as the following [9]:

(6)

where n1 and n2 are the number of samples in period 1 and period 2. X1 and X2 are the mean

values for period 1 and 2 respectively. Sp is the so-called pooled variance that has the

following expression:

Sp

(7)

where S1 and S2 are the variances for period 1 and 2.

3.5 Focus group interviews

To get an interpretation as correct as possible of how the DoseAware System has influenced

the staff’s working methods focus group interviews were performed after the second data

collection period. The purpose was also to find methods to give the staff better feedback in

their work.

With guidance from Communication and Learning, the Department of Education, University

of Gothenburg, a questionnaire was developed and was used during the interviews. The

questionnaire can be seen in Appendix 2.

During the interviews, the staff’s PCI procedures earlier the same day were discussed and

some dose graphs from the procedures were shown.

4 Results

The total number of procedures that were analyzed during the two periods was 153 (99

coronary angiographies and 54 PCI). One of the procedures was a pressure measurement but

was included as an angiography since the fluoroscopic time and the KAP-value were similar

as an angiography procedure. Two emergency procedures (1 angiography and 1 PCI) were

performed in Period I, and there were 2 emergency PCI in Period II and in one additional

case, the patient had a heart attack and cardiac arrest during a procedure.

Table 3 shows a summary of the two data collection periods.

18

Table 3. Summary of the data collection from the first and second period. The table shows the number of

procedures that has been performed. It also shows the accumulated total KAP(KAPfluoroscopy + KAPangiography series),

the total fluoroscopic time, total number of generated image series and the accumulated PDM dose for each

operator and period.

Figure 7 shows the distribution of the patients’ weights and the fluoroscopic times per

procedure in both the data collection periods. The number of procedures was 76 in Period I

and 77 in Period II. Since there was a loss in weight information in Period I, only data from

75 patients are included in the weight distribution graph.

a)

b)

Figure 7. The distributions over the patient weights (a) and the fluoroscopic times (b) per procedure for the two

data collection periods. Weights from 75 patients were included in Period I since there was a loss in

information.

0

5

10

15

20

≤ 50

> 5

0-5

5

> 5

5-6

0

> 6

0-6

5

>65-

70

> 7

0-7

5

> 7

5-8

0

> 8

0-8

5

> 8

5-9

0

> 9

0-9

5

> 95

-100

>100

-105

> 10

5-1

10

>110

-115

>115

-120

>120

-125N

um

ber

of

pat

ien

t

Weight intervals [kg]

Period I

Period II

0

5

10

15

20

Nu

mb

er o

f p

roce

du

res

Fluoroscopic time intervals [min]

Period I

Period II

Operator Red

Operator Green

Operator Blue

Total

Period

I

II

I

II

I

II

I

II

Coronary angiography 19

12

17

28

12

11

48

51

Angiography + PCI

8

8

12

10

8

8

28

26

KAPtot [Gycm2]

1150

927

1467

1590

950

592

3567

3109

Total fluoroscopic time

[min]

156

133

238

247

157

104

551

484

Number of image series

419

380

415

514

285

231

1119

1125

Accumulated PDM dose

[µSv]

558

495

60

307

1957

900

2575

1702

19

The median weight was 78 kg in Period I (mean: 79 kg) and 80 kg in Period II (mean: 80 kg)

and there was no statistically significant difference (p = 0.73). The median fluoroscopic time

per procedure was 5.5 minutes in Period I (mean: 7.3 min) and 4.1 minutes in Period II

(mean: 6.3 min). In Period II, there seems to be a shifting in fluoroscopic time towards a

shorter exposure time, even though this difference was not statistically significant (p = 0.27).

4.1 Kerma Area Product (KAP) and reference PDM

It seems to be a linear relationship between the reference PDM on the C-arm and KAP, i.e.

the PDM dose increases when KAP increases and this can be seen in Figure 8. This means

that the values from the reference PDM potentially could be used as a relative measure of

KAP if KAP values were not available.

c

Figure 8. The relationship between the reference PDM-doses and KAP.

The median dose rate per procedure for the reference PDM was around 400 µSv/h at the

distance of 1 meter from the beam field. This means that a PDM would not in general register

any dose rates at a distance of 3 meters from the radiation source, since it only registers dose

rates > 40µSv/h.

4.2 Patient doses

The median effective dose to the patients per procedure in the two periods was calculated,

depending on which operator has performed the procedure. Operator Green and Blue have

decreased their KAP per, which also lead to a decrease in effective dose. The difference was

however only statistically significant for operator Blue (p: 0.036). The median effective doses

and KAP values are shown in Table 4.

y = 1,7678xR² = 0,8854

0

100

200

300

400

500

0 50 100 150 200 250 300 350

Do

ses

fro

m t

he

refe

ren

ce P

DM

[u

Sv]

KAP [Gycm^2]

20

Table 4. The median effective dose per procedure and KAP per procedure for the two periods depending on which operator that has performed the procedure .

*= statistically significant different

Operator Red Operator Green Operator Blue

KAPmedian per procedure

in Period I [Gycm2]

34

41

37

KAPmedian per procedure in Period II [Gycm

2]

38

32

28*

E median per procedure in

Period I [Gycm2]

6.2

7.3

6.6

E median per procedure in

Period II [Gycm2]

6.9

5.9

5.0*

The median KAP for all procedures (including all the operators) in Period I was 35.4 Gycm2

(mean: 47.4 Gycm2) and 32.6 Gycm

2 for Period II (mean: 39.8 Gycm

2). KAP at the third

quartile for Period I was 41 Gycm2 and the corresponding value for Period II was 39 Gycm

2.

The distribution of KAP for all procedures in Period I and Period II can be seen in Figure 9.

The figure shows that 4 procedures have generated KAP values that exceeded the first action

level, whence one procedure even exceeded the second action level.

h

Figure 9. The distribution of KAP per procedure for all procedures in both periods. The orange crosshatched

line marks the first action level (skin dose 2 Gy) , and the red line marks the second action level (skin dose 3 Gy).

0

50

100

150

200

250

300

0 20 40 60 80 100 120 140 160

KA

P [

Gyc

m2]

Procedure number

First action level

Second action level

21

4.3 Personnel doses

4.3.1 Operator doses

According to Table 3, the accumulated PDM dose to the operators decreased from Period I to

Period II for two of the operators. When comparing the two periods, only operator Blue has

decreased his median PDM-dose per procedure, which was statistically significant different (p

= 0.023).

Table 5 summarizes the median values for PDM dose; PDM dose/KAP; KAPtot (=

KAPfluoroscopic + KAPangiography series), KAPfluoroscopic/ fluoroscopic time and fluoroscopic time .

Table 5. Median values per procedure for PDM dose, PDM dose/KAP, KAPtot, KAPfluro/ fluoroscopic time and

fluoroscopic time for each operator in the two periods.

*= statistically significant different

The operators’ PDM doses per procedure versus KAP, i.e. how much radiation that has been

detected by the PDM (hit the operator) compared to the total radiation emitted from the X-ray

tube, is illustrated in Figure 10. The figure shows that there is a difference in the amount of

received PDM dose between the operators, but there is a general correlation between KAP

and PDM dose.

Median values per

procedure

Operator Red

Operator Green

Operator Blue

Period

I

II

I

II

I

II

PDM dose [µSv]

11

19

1

1

74

29*

PDM dose/KAP [µSv/Gycm

2]

0.32

0.51

0.031

0.037

1.6

1.5

KAPtot [Gycm2]

34

38

41

32

37

28*

KAPfluoro/fluoroscopic time [Gycm

2/min]

1.8

1.8

1.7

1.9

2.2

1.7

Fluoroscopic time

[min]

4.7

5.8

5.5

3.6

7.1

3.1

22

V

Figure 10. The three operators’ PDM doses versus KAP.

4.3.2 Nurse doses The doses to the nurses when they were assisting a procedure are shown in Figure 11 where

their doses are plotted versus the KAP-values.

Figure 11. Doses to the assisting nurses per procedure versus KAP per procedure.

The dose graph shows that there is a clear reduction in PDM dose during Period II, and this

difference is statistically significant (p = 0.017). The median dose in Period I was 4 µSv

(mean dose: 6.5 µSv) and 2.5 µSv in Period II (mean dose: 3.9 µSv).

Table 6 shows the median PDM dose per procedure for the assisting nurse in both the periods.

The values were divided into which operator that performed the procedure. There was a

0

50

100

150

200

250

300

350

0 100 200 300 400

Do

se t

o t

he

op

erat

or [

µSv

]

KAP [Gycm^2]

Operator Red

Operator Green

Operator Blue

y = 0,1464xR² = 0,4903

y = 0,0958xR² = 0,2293

0

5

10

15

20

25

30

35

0 50 100 150 200 250

Do

se t

o t

he

ass

isti

ng

nu

rse

[µSv

]

KAP [Gycm^2]

Period I

Period II

23

statistically significant difference in dose between the periods when operator Red was

working (p = 0.05).

Table 6. The median PDM dose per procedure for the assisting nurse in Period I and Period II depending on which operator that has performed the procedure.

*= statistically significant different

Operator Red

Operator Green Operator Blue

Assist.nurse PDM dose

/KAP in Period I

[µSv/Gycm2]

0.11

0.13

0.095

Assist.nurse PDM dose /KAP in Period II

[µSv/Gycm2

0.077*

0.10

0.055

Doses per procedure to the “wait on” nurse and the patient responsible nurse were very low.

For “wait on” nurses, the median dose per procedure was 0 µSv (mean dose: 2.2 µSv) in

Period I and the median dose in Period II was 0 µSv (mean dose: 1.5 µSv). The median dose

for the patient responsible nurses was 0 µSv per procedure (mean dose: 1.3 µSv) in Period I,

and the median dose was 0 µSv in Period II (mean dose: 0.9 µSv).

Figure 12 shows the accumulated doses for the nurses when they worked as “wait on” or were

patient responsible. The figure also shows how many procedures that a nurse has been

participated as “wait on” or patient responsible. Nurse number 3 and number 6 have the

highest accumulated doses.

Figure 12. The diagram on the left shows the accumulated doses for each nurse when he or she worked as “wait

on” or was patient responsible during a procedure. The right diagram shows how many procedures the nurses

have been working as “wait on” or patient responsible.

24

4.3.3 Collective doses, effective doses and eye doses

In Period II, there has been a lowering in collective PDM dose for the operators, as well as for

all the working roles for the nurses. The reduction in total collective dose was 34 % and Table

7 shows the collective doses for both the data collection periods.

Table 7. The collective doses for both the data collection periods.

Operators Assisting nurses

“Wait-on” nurses

Patient responsible

nurses

All

Collective PDM

dose in Period I [µSv]

2601

408

129

83

3221

Collective PDM

dose in Period II [µSv]

1702

256

112

69

2153

The table above shows that there has been a reduction in doses in Period II for all the working

categories’ but a statistic significant difference could only be determined for doses to the

assisting nurses (p = 0.016).

The correlation factor Dforehead/ Dthorax was calculated. The maximum ratio was determined to

0.11 for operators, and 4 for assisting nurses.

The estimated annual doses, effective doses and eye doses for the operators and the nurses can

be seen in Table 8.

Table 8. Estimated annual doses, effective doses and eye doses for the operators and the nurses.

Assisting

nurses

PDM doses

[µSv/year]

“Wait on” &

pat.resp. nurses

PDM doses

[µSv/year]

Total PDM

dose [µSv/year]

Effective

dose

[µSv/year]

Eye dose

[mSv/year]

Nurse 1 800 200 1000 30 3,6

Nurse 2 380 28 408 12 1,7

Nurse 3 840 1300 2140 64 3,7

Nurse 4 560 180 740 22 2,5

Nurse 5 180 11 191 6 0,80

Nurse 6 450 470 920 28 2,0

Nurse 7 100 11 111 3 0,45

Nurse 8 570 13 583 17 2,5

Nurse 9 140 72 212 6 0,62

Nurse 10 180 61 241 7 0,80

Ope. Red 5800 174 0,65

Ope. Green 2000 60 0,22

Ope. Blue 16000 480 1,8

25

4.4 Focus group interviews

All operators and 5 nurses participated in the interviews.

Their first impression of the DoseAware System was positive and one cardiologist wondered

“why hasn’t this system come earlier?”. Another cardiologist thought that this system in a

long-term could help them minimize the amount of unnecessary radiation. The expectations

were high since this was the first time they could “see” the radiation, and they expected to

become better in choosing “good” projection angels and be better in positioning themselves in

relation to the radiation source. They were also excited to see how their dose rate bars would

reflect their actions. One nurse said that in the first period, she began to wonder if she was

working in the same way as she used to, or if she was actually trying to work more “radiation

hygienic” since she started to wear the PDM. But they all tried to work as normal as possible

in Period I.

The radiation protection awareness has changed, and the nurses have many times found

themselves standing in what they thought, was a good position but the bars showed instead

high dose rates. They did earlier think that just one step back from the examination table

would lead to minimum doses, and the nurses were surprised that they sometimes got higher

dose rates than the operator. So the system has helped them to find better positions where they

are better shielded from the radiation. One cardiologist said that he earlier did not consider

how the projection angle would affect his and his coworker’s doses, but the visualization has

helped him get more aware of what angles that gives more or less radiation. The colors on the

bars also had a psychological effect because no one wanted red bars. He also thought that the

bars woke the competition instinct; everyone tried to get as little dose as possible. So seeing

the dose rates helped the nurses change their positions, and the operators did more often

change the ceiling suspended screen in a better shielding position. The staff found out that the

dose rates could be quite high if one stands in the doorway to the control room; and they used

to stand there very often without wearing lead aprons! A doctor said that it was a pity that

study period was too short, because it takes time to change your working habit.

The working moments that was considered to be connected to greater risk for radiation

exposure, were during PCI and if the procedure was complicated or emergency. A doctor said

the choice of the projection angle plays a role in the amount of scattered radiation, but she did

not always have the possibility to choose the angle that would give least dose. The assisting

nurse is quite fixed near the table during a PCI and does not have the same possibility to take

a step backward like during conducting image series. A doctor said he often forgot to check

the base station during a complicated PCI, and another doctor thought the system would be

best useful during “standard procedures” when he had more “free time”.

Before the DoseAware system was introduced, the staff had theoretical knowledge about

radiation protection and they have a good collaboration with their physicist. They knew that

the longer distance to the radiation source the better, and the operators tried to keep the

fluoroscopic time as short as possible. But they could not until recently see the effect of the

protection actions.

The staff did not before think that they needed to change their working methods, but they

knew that they could optimize it, and that is why some of them have been involved during

purchases of better lead aprons, protection screens, etc. When discussing the dose graphs, the

staff was very surprised that there was such a big difference in dose rates between a standard

26

procedure, and when the patient was having a cardiac arrest. They thought that regular follow-

ups of personal doses and also seeing dose graphs could maybe improve their knowledge in

radiation protection, and one doctor thought that the greatest gain in personal dose happened

while dealing with a procedure. He thought that 80-90 % benefit lied in seeing the current

dose exposure so that one could take actions, while 10-20 % benefit lied in retrospective

analysis of the dose graph. Some nurses thought that it could be difficult to remember what

had happen during a procedure if you are not analyzing the graph straight after the procedure.

Analyzes are also unfortunately a matter of time.

One potential risk of having this kind of system for a longer time is that one might stop

looking at the base station, but a doctor thought that such a behavior not only was bad. That

could be a good sign that the staff was feeling more secure in their working methods and less

needed to look at the base station to see what the radiation exposure was like. Another doctor

thought you only need to see a flash of a red bar in the corner of your eye to make you react.

The staff thought that the base station could have been better integrated with the other

monitors. It is best positioned when they can see the patient image and still to see the dose

bars with a small eye movement. Another request was to a get a dose graph automatically

after a procedure so that everyone involved could see their dose history and accumulated

doses.

They did not think that it was difficult to handle the DoseAware system and prior knowledge

was not necessary. It was more important to have an interest in how you better could protect

yourself and your colleagues from radiation. They also thought that while using this kind of

system, it would be good if a physicist or someone else having good knowledge in radiation

protection could give the staff feedback and help them interpret their dose graphs.

5 Discussion

The distribution of the patient weights in the two periods was very similar which made it

easier to compare the two periods. A clear difference in fluoroscopic time could not be

established, although one could say that there was a slight shift towards shorter fluoroscopic

times (≤ 4 minutes) in Period II. One potential explanation to why there is no clear difference

in fluoroscopic time between the periods could be the short data collection time. It takes time

to learn new working routines, four weeks were not enough. Another reason could be that the

operators already (i.e. before this project) are irradiating as little as they possibly can, and a

further reduction in fluoroscopic time is sometimes not possible.

5.1 Kerma Area Product (KAP) and reference PDM

There was a linear relationship between KAP and the reference PDM on the C-arm, so the

PDM dose could potentially be used if KAP was unknown. Both the reference PDM and KAP

are responded to the X-ray tube’s dose mode settings, the beam collimation and the geometry

of the patient, but one disadvantage is that the reference PDM also is dependent on the

projection angle. The reference PDM is thus more suitable to indicate the amount of radiation

that would hit the staff if they would not stand shielded behind a protection screen or be

positioned at a long distance from the radiation source.

27

5.2 Patient doses

Table 4 showed that there was no big change in doses to the patients between the two periods,

although operator Blue has decreased his patients’ median effective dose with 24 %, based on

a decreased median KAP with 24 %. The difference is statistically significant. Figure 9

showed that only 4 procedures generated KAP values over the action levels, which confirms

the skills of the operators.

SSM has received reported standard radiation doses to the patients for different types of X-ray

examinations from 39 hospitals in Sweden, and has determined a diagnostic reference level

(DRL) at 80 Gycm2 for coronary angiographies [10]. The reference level was set so that 75%

of the performed examinations in Sweden gave a lower KAP-value. Figure 13 shows the

distribution of standard doses for coronary angiography procedures in Swedish hospitals.

The resulted median KAP for an angiography procedure, would place Halmstad Hospital in

the bar of > 40-50 Gycm2

for Period I, and in > 30-40 Gycm2

for Period II. This shows that

the Halmstad operators have generated lower KAP per coronary angiography procedure than

SSM’s diagnostic reference level.

Figure 13. The distribution of reported standard doses for coronary angiography in Swedish hospitals. The

figure also shows the resulted median doses for this kind of procedure in Halmstad Hospital in Period I and

Period II.

It is quite easy to explain why operator Green in one procedure in Period I generated over 300

Gycm2. The staff did not register anything unusual about that procedure in the protocol, but

the fluoroscopic time was relatively long (25 minutes). The median number of angiography

series was 13 for both the data collection periods, but in this procedure, 45 image series were

conducted which explains the high KAP value. Operator Red also had a procedure in Period I

that gave a KAP value over 200 Gycm2. The reason to this was the relatively long

fluoroscopic time (23 minutes) and the fact that 39 angiography series were conducted.

28

5.3 Personnel doses

5.3.1 Operator doses

The resulted PDM dose per procedure showed that the three operators have different working

methods.

In Period I, operator Green’s accumulated PDM dose was more than 30 times less than

operator Blue’s, even though operator Green had performed more procedures and also had the

highest accumulated KAP-value.

The explanation to this confusing result was operator Green’s working method. Unlike the

other two operators, operator Green often sits on a chair during his procedures, and the table

suspended protection screen was pulled up so that the operator could lean on it. Figure 14

illustrates his working position.

Figure 14. Operator Green’s working position. The operator usually sits on a chair during his procedure

and the table suspended protection screen is pulled up which shields his PDM.

In this position, the table suspended protection screen almost completely shields both the

operator and the PDM from the scattered radiation, thus the registered dose was very low. The

advantage with this working position is that the radiation sensitive organs are well protected

from the scattered radiation since the front body is very close to the protection screen.

One explanation to why operator Green’s doses have increased during Period II was that he

could not always see his dose bar on the base station when he was sitting, so he had to stand

up and the table suspended screen was then no longer as good in shielding his thorax area as

when he was sitting down. This operator was also working during two emergency procedures,

but the registered PDM doses did not diverge (1 µSv in both procedures) from his “standard”

procedures (mean dose: 1 µSv).

29

A statistically significant difference in PDM doses could only be determined for operator

Blue. This operator had the highest PDM dose in Period I which has been reduced with about

61 % during Period II (p = 0.023). The difference in PDM dose was statistically significant

even though this operator had a patient in Period II who had a cardiac arrest which gave the

operator a PDM dose of 229 µSv. Such PDM dose would equal an effective dose around 7

µSv and since this kind of situation fortunately only occurs a few times per year, there is no

high risk that the operator will exceed the dose limit for effective dose (50 mSv/year).

Operator Red had a slightly increase in almost all the studied parameters (PDM dose, PDM

dose/KAP, etc) in Period II, but since this operator performed seven procedure fewer

compared to Period I, the statistically uncertainty is very high so the increase in dose might

just be a coincidence.

5.3.2 Nurse doses

Also the assisting nurses had a statistically significant difference in dose per KAP in Period II.

The visualization of dose bars has helped them to improve their working positions. This

difference was more distinct for the assisting nurses than for the operators, because the nurses

are often more free to change their position, and are also recommended to stand behind the

operator. The operator on the other hand works more close to the radiation source even

though he or she is sometimes better shielded behind the ceiling suspended screen than the

assisting nurse. This difference was not caused by the fact that the operator had lowered the

KAP, since the difference in PDM dose/KAP was statistically significant when operator Red

was working, but the change in KAP per procedure between the two periods was not

statistically significant.

Table 7 showed that the accumulated doses to “wait on” nurses were higher than for patient

responsible nurses, but there were no statistically significant differences in doses to the “wait

on” nurses or to the patient responsible nurses between the two periods. These working

categories did not receive so much dose since they were positioned outside the angiography

room or sat behind a radiation protection screen during the majority time of the procedures.

Nurse 3 worked as “wait on” and Nurse 6 was patient responsible during the procedure when

the patient had a cardiac arrest. Nurse 3 thus got a PDM dose of 73 µSv and Nurse 6 got 32

µSv, so their annual PDM doses are overestimated. Nurse 3 has clearly changed her working

behavior in Period II, and if the received dose from the procedure where the patient had a

cardiac arrest were subtracted, her accumulated dose would be reduced to only 15 µSv in

Period II.

There has been some loss in dose information to the nurses. Only one nurse had a personal

lead apron where the PDM constantly could be positioned in the pocket. The remaining nurses

had personal thyroidal protections where they attached their PDMs on. The consequence was

(especially during Period I when they could not see their dose bars) that the PDM sometimes

got tucked under the lead apron, and did not register any dose rates.

In Period I, there was a loss of dose information to the assisting nurses for 11 procedures. 6 of

the losses were caused by the malfunction of one nurse’s PDM (Nurse 1) and the remaining

losses were caused by the fact that the PDM got tucked under the lead aprons. There were

further information losses when the Nurse 1 worked as “wait on” nurse (8 times) and patient

responsible (6 times).

30

In Period II, there were 11 dose information losses in dose to the assisting nurse. 8 of them

were caused by a repeated malfunction of Nurse 1’s PDM, the rest was caused by having the

PDM inside the lead apron, and in 2 cases the nurse forgot to wear her PDM. There was also a

loss in dose information when the Nurse 1 worked as a “wait on” nurse, and one additional

time when she was patient responsible.

The number of losses in dose information for the assisting nurse was the same in both periods,

so this error in both the periods cancels each other out. The loss in dose information for the

other two working roles for the nurses was not so crucial since these nurses do not receive

much dose during a standard procedure.

5.3.3 Collective doses, effective doses and eye doses The collective dose in Period II was about 34 % less than Period I. The estimated collective

dose to the nurses had some error factor since the PDMs sometimes are placed under the lead

apron or for one unfortunate nurse, did not work. The estimated annual PDM dose for Nurse

1has been scaled up, but would have a greater uncertainty than for the rest of the nurses. An

estimated annual PDM dose with much uncertainty would also consequently lead to an

estimated effective dose with big uncertainty. However, Table 8 shows that the calculated

effective doses are far from the dose limit for all staff member.

The Dforehead/Dthorax - factor was not the same for operators and assisting nurses. The maximum

ratio was 0.1 for the operators and 4 for the assisting nurses and this was based on only 15

ratios. This big difference is very hard to explain, but perhaps the ceiling suspended

protection screen was a good shield against the scattered radiation that would otherwise hit

the operator’s PDM on the forehead. The assisting nurse is often poorly protected by the

ceiling suspended screen, hence the bigger Dforehead/Dthorax - ratio.

The biggest error lies in the poor number of Dforehead/Dthorax - ratios, and this kind of estimation

would be more accurate if small TLD instead would be placed on the staff’s forehead during

every procedure. Table 9 also shows however that none of the staff member is near to exceed

the dose limit for the lens of the eye.

The calculated doses to the lens of the eye are quite uncertain since this was based on only 16

quotas but beside that, the DoseAware System could be a acceptable tool to estimate the eye

doses.

31

6 Conclusions

The dose to the patients has been reduced, since the median KAP/procedure in Period II has

been reduced with 24 % for one operator and the median effective dose has lowered with 24

%.

The Dose Aware System has changed the personal doses. One operator has lowered his

median PDM dose per procedure with about 61 % in Period II and this was statistically

significant. The system has also reduced the assisting nurses’ median dose per procedure with

38 % which also was statistically significant.

A decrease in collective doses for all the working categories has been registered in Period II.

The reduction was 35 % for the operators; 37% for the assisting nurses; 13% for the “wait on”

nurses and 17% for the patient responsible nurses. The estimated eye doses showed that

neither of the staff members has received an eye dose near the dose limit (the highest

estimated eye dose was 3.6 mSv/year).

As a result from the focus group interviews, the personnel thought that the DoseAware

System has improved their radiation awareness. The system has helped them to better use the

radiation protection screens, and helped them to find better working positions.

32

Acknowledgements

I would like to thank my two supervisors Charlotta Lundh and Åke Cederblad at the

Department of Medical Physics and Biomedical Engineering, Sahlgrenska University

Hospital, for their guidance and support that have de-dramatized my worries about performing

a study. Also thanks to Magnus Båth at the Department of Medical Physics and Biomedical

Engineering, Sahlgrenska University Hospital for his thoughts and aspects.

I would also like to thank Hans Rystedt at Communication and Learning, the Department of

Education, University of Gotherburg for his help with the focus group interviews.

A warm thanks to Mikael Bergfjord, my supervisor and friend at Unfors Instruments AB who

has helped me with all the technical issues.

A special thank you to the lovely people in the PCI laboratory in Halmstad Hospital who

made me feel welcome every Wednesday and made this study possible.

Finally, I want to gratefully acknowledge my friends and family: thanks for your

encouragements!

33

References [1] ICRP. Recommendations of the International Commission on Radiological Protection,

Publication 103. Annals of the ICRP, Elsevier, 2008

[2] Vano, Eliseo, Norman J Kleiman, Ariel Duran, Madan M Rehani, Dario Echeverri, and

Mariana Cabrera. "Radiation Cataract Risk in Interventional Cardiology Personnel."

Radiation Research, 2010

[3] Almén, Anja, Torsten Cederlund, och Britta Zaar. SSI Rapport 2005:06 Percutan coronar

intervention PCI - en strålskyddsutredning av verksamheten på landets sjukhus. Stockholm:

SSI, 2005

[4] ICRP. Avoidance of Radiation Injuries from Medical Interventional Procedures,

Publication 85. Annals of the ICRP, Elsevier, 2000

[5] SSM. SSMFS 2008:51 Strålsäkerhetsmyndighetens föreskrifter om grundläggande

bestämmelser för skydd om arbetstagare och allmänhet vid verksamhet med joniserande

strålning. SSM, 2009

[6] Strålskyddsfrågor, Nordisk rapportserie on. “No 5 Nordic guidance levels for patient doses

in diagnostic radiology.” 1996.

[7] Bogaert E, Bacher K, et al. “A large-scale multicentre study of patient skin doses in

interventional cardiology: dose-are product action levels and and dose reference levels.” April

2009.

[8] Padovani, R, och C. A. Rodella. ”STAFF DOSIMETRY IN INTERVENTIONAL

CARDIOLOGY.” Radiation Protection Dosimetry, 2001: 99-101, Vol. 94.

[9] Arnold, Jesse C, and J. Susan Milton. Introduction to probability and statistics. New

York: McGraw-Hill, 2003

[10] Almén, Anja, och Wolfram Leitz. SSI Rapport 2008:02 Patientstråldoser vid

röntgendiagnostik i Sverige - 1999 och 2006. Stockholm: SSI, 2008

34

Appendix 1

Protocol

Date Type of procedure Time of start and end Tot. fluoroscopic time

min

KAPfluoroscopic & KAPangio series Gycm2| Gycm2 Number of angiography series

Patient’s length & weight cm| kg

Operator

Assisting nurse ”Wait on” nurse Patient responsible nurse Another Carrier of the forehead-PDM

Comments and remarks

35

Appendix 2

Focus groups Personnel – Questioning guide

Presentation of the purpose about the interview

Opening questions

Would you like to tell us your name and what your work task was during this

morning?

Introductory questions

What was your first impression about using this system?

Transition questions

Is there a difference in your radiation protection awareness now that you have used

this system for a couple of weeks, compared to before?

Key questions

During what working moments are the risk of being exposed to radiation greatest?

Before you had this system, how did you know what working moments that were

connected with the risk of being exposed to high dose rates?

Has your daily work somehow changed since this system was introduced?

o Is there any working moments that especially has been affected?

o Describe how you found out that you needed to change your working methods.

Discuss the dose graphs from today’s working periods:

o (First, explain the graphs)

o What are your reactions to this?

What could be improved?

o Regarding the system’s design and functions?

o The way it has been introduced and used?

Is prior knowledge necessary?

Would regular follow-ups be a method to improve radiation protection

and routines?

Ending questions

Is there anything, for example experience or suggestions to improvements that are

important in this context, which has not appeared in the interview?

Do you have any reflections about this discussion?

Is there anything you would like to add?