dosimetric audit of treatment planning systems...treatment planning and delivery processes. the...

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IAEA supported national audit of treatment planning systems

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FOREWORD

Quality Assurance in the radiation therapy treatment planning process is essential to ensure accurate dose delivery to the patient and to minimize the possibility of accidental exposure. According to IAEA Safety Report Series no.17 [1] treatment planning and beam calibration are the main sources of errors in external beam radiotherapy.

The IAEA has a long history of providing assistance for dosimetry audits in radiotherapy to its Member States. Together with the World Health Organization (WHO), it has operated postal audit programs using thermoluminescence dosimeters (TLD) to verify the calibration of radiotherapy beams since 1969.

The objective of this IAEA supported national dosimetric audit is to ensure the optimal usage of radiotherapy Treatment Planning Systems (TPS) and safe radiotherapy.

The present document was tested through the pilot study in radiotherapy facilities of different sizes by the participants of the IAEA Coordinated research project E2.40.13

“Development of procedures for quality assurance for dosimetry calculation in radiotherapy” in order to test its feasibility. The audit is based on IAEA TECDOC 1583 “Clinical Commissioning Protocol for Radiotherapy Treatment Planning Systems (TPS)” [2] and in accordance with IAEA TRS 430 [3].

Acknowledgement

Major contributions to the basis of this work by Stanislav Vatnitsky (IAEA), Eduard Gershkevitsh (Estonia), Rainer Schmidt (Germany), Graciela Velez (Argentina), Daniel Miller (USA), Erhardt Korf (South Africa), Fernando Yip (Cuba), Somsak Wanwilairat

(Thailand) is gratefully acknowledged.

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CONTENTS

1.INTRODUCTION…………...……………………………………………………………………………………...... 4 1.1 BACKGROUND..........................................................................................................................................................4 1.2 PURPOSE .................................................................................................................................................................4 2.1 REQUEST FOR AUDIT ..............................................................................................................................................4 2.2 GUIDING PRINCIPLES AND PROCEDURES OF THE AUDIT ......................................................................................5 2.3 THE AUDIT REPORT .................................................................................................................................................5

3.2.1. Anatomical and input test cases ........................................................................................................................8 3.2.2. Dosimetric test cases ...........................................................................................................................................9 Case 1: Confirmation of the basic beam data based on CT data ................................................................... 10 Case 2: Oblique incidence, lack of scattering and tangential field.................................................................. 10 Case 3: Significant blocking of the field corners ................................................................................................. 11 Case 4: Four field box ............................................................................................................................................... 12 Case 5: Customized blocking .................................................................................................................................. 13 Case 6: L shaped field with oblique incidence..................................................................................................... 14 Case 7. Three field plan with asymmetrical fields and wedges....................................................................... 15 Case 8. Plan with non-coplanar field. .................................................................................................................... 16 Case 1A: Large field (optional test) ........................................................................................................................ 17 Case 1B: Extended SSD (optional test) ................................................................................................................ 18

REFERENCES...............................................................................................................................................19 Appendix 1 Questionnaire/request for audit....................................................................................... 20 Appendix 2: On site questionnaire

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1 INTRODUCTION

1.1 Background

Independent external audits are a necessary part of a comprehensive quality assurance (QA) programme in radiation oncology [4-6]. Different audits have been described in various IAEA and peer-reviewed publications [7-9] addressing dose measurements and

other important medical physics related procedures.

The audit methodology presented here puts an emphasis on the dosimetry part of the treatment planning and delivery processes. The methodology simulates the important parts of the external beam radiotherapy workflow, from patient data acquisition to

treatment planning to dose delivery. This audit utilizes an anthropomorphic phantom in a set of clinical test cases prepared by the IAEA, covering a range of typical clinical radiation delivery techniques in 3D conformal radiotherapy treatment (3D CRT).

1.2 Purpose

The purpose of the IAEA supported national audit is to review the dosimetry part of the

3D CRT planning and radiotherapy delivery processes in Member States. Clinical issues related to these processes are beyond the scope of the audit. Also, issues related to intensity modulated radiation therapy, electron therapy or other specialized techniques are not addressed in the audit.

The process begins with the phantom being scanned using computerised tomography (CT). The scan data is then transferred to the TPS where the different clinical test cases are planned. Once the plans are ready the phantom is treated using them, and dosimetry within the phantom is performed. The comparison of planned doses with the measured

ones is the ultimate result of this audit.

The audit is not aimed at benchmarking a particular dose calculation algorithm on the TPS, but rather to evaluate the overall performance of the system, which is more relevant to the clinical situations. The results will provide the hospital with assurance that the

beam-specific parameters in the clinically used algorithms of its TPS are correctly set, and that the doses calculated with the model agree within predefined limits with the measured data.

2 AUDIT STRUCTURE

2.1 Request for audit

The IAEA supported national TPS audit in radiotherapy is voluntary. The local auditing organisation should discuss strategies and collect audit requests during their national workshop on TPS audits. The institution requesting an audit must have the basic equipment and infrastructure to deliver good quality radiotherapy. This should include

high energy teletherapy units, a computerised TPS, and access to a CT imaging facility. The audit is not structured to provide the commissioning of a new TPS. The hospital should have completed acceptance testing and commissioning of a TPS and teletherapy machine, and have them ready for clinical operation. If a TPS is connected to other

devices through a network, accurate data transfer and possible data translation and conversion should be checked by the user in advance.

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To request consideration for the audit, the form in Appendix 1 needs to be completed and

submitted. Appendix 2 will be filled on site (at audit location) and will be included in the “TPS Results evaluation sheet” file.

2.2 Guiding principles and procedures of the audit

The audit procedure is based on the use of a CIRS thorax phantom Model 002LFC

(Norfolk, VA). The phantom is equipped with a set of calibrated electron density reference plugs that enable the verification of the Hounsfield Units/electron density conversion procedure. The clinical test cases cover a range of typical clinical techniques of 3D CRT.

The tests are structured so that at first, the dose distributions for single beams are considered, then standard multiple field techniques are used, and finally complex multi-field arrangements are applied. These checks are primarily aimed at confirming the planned absolute doses delivered to the phantom agree with those as determined by

measurement.

The audit takes about 10-15 hours for one teletherapy unit, depending on the machine itself. Issues affecting this time include the machine’s energy (single or dual energy), the availability of the record and verify system, the automatic set-up functionality, the number

of calculation algorithms in the TPS, etc. Usually a machine’s audit will span over 2 days. On the first day the CT scanning and test case planning is performed. CT scanning will require about 45 min of CT scanner time and test case planning together with printing and the transfer of data to the linac record and verify system would require about 5 hours of

TPS time depending on number of calculation/inhomogeneity correction algorithms and calculation speed. On the next day the irradiation of the phantom will take place, which will require up to 5 hours of linac time for a dual energy machine. A maximum of two teletherapy machines can be evaluated during a single visit.

The time scale indicated above is required to perform eight different clinical test cases during the audit. Extra test cases could be added as requested by the hospital to account for specific techniques; however this would extend the time required on the TPS and the treatment machine.

During the allotted times, the auditors should have a free access to the TPS workstation with calculation capabilities as well as the to the treatment machine to perform the measurements. A one hour time slot should be reserved on the CT for phantom scanning.

The auditor will bring with them the IAEA phantom. A calibrated ionization chamber and

electrometer needs to be provided by the local auditing organization.

2.3 The audit report

The preliminary results will be handed over to the audited centre at the end of the audit.

Any discrepancies discovered (dose deviations exceeding agreement criteria) would be reviewed and possible explanations may be found while the auditor is still on site. Follow-up visits could be arranged if applicable.

The final audit report will be submitted within four weeks after completion of the audit. The report will be sent only to staff in responsible positions in the radiotherapy department, e.g., the chief medical physicist and other staff members whose role in the institution is

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significant to this audit. At all times the audit reports are confidential.

The resolution of any discrepancies discovered during the TPS audit is the responsibility of the audited hospital.

3 AUDIT METHODOLOGY

3.1 Phantom

The CIRS Thorax phantom (Figure 1) is elliptical in shape (30 cm long x 30 cm wide x 20

cm thick) and represents an average human torso in proportion, density and two-dimensional structure. The phantom has soft tissue, lung and bone sections with holes to hold interchangeable rod inserts. Interchangeable tissue equivalent rod inserts accommodate ionization chambers allowing for point dose measurements in multiple

planes within the phantom. The placement of holes allows verification in the most critical areas of the chest. One half of the phantom is divided into 12 sections, each 1 cm thick, to support either radiographic or radiochromic film. Handling, assembly and proper orientation of the phantom is assisted by the use of an alignment base and holding

device. The phantom is equipped with a set of five calibrated electron density reference plugs (Table 1).

Table 1. Characteristics of calibrated electron density reference plugs

Density (g/cm3) Electron density

per cc x 10 2̂3

Electron density relative

to water

Lung 0.21 0.69 0.207

Bone 1.60 5.03 1.506

Dense bone 2.17 6.70 2.005

Muscle 1.06 3.48 1.042

Adipose 0.96 3.17 0.949

The measurements are performed by placing the calibrated ionization chambers into the different holes in the phantom. Although the phantom has a capacity to accommodate films for the measurement of dose distributions, this function is not included in the present

audit methodology.

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Figure 1. Thorax Phantom (CIRS Model 002LFC).

The holes in the phantom are labelled to identify the locations of the points of measurement within the phantom, thus enabling the comparison of the TPS calculations and the measured values. The recommended labelling of the holes and the

recommended arrangement of the calibrated electron density reference plugs during CT scan is given in figure 2.

Figure 2. Thorax phantom showing labeling scheme of holes and recommended arrangement of the calibrated electron density reference plugs during CT scan. Plug 1-muscle substitute, plug 2 – bone substitute, plug 3 – syringe filled with water, plug 4 –

adipose substitute, plug 5 – water equivalent, plug 6 – lung substitute, plug 7 – air, plugs 8 & 9 – lung substitute, plug 10 – dense bone substitute.

3.2 Clinical test cases

The clinical test cases cover range of typical 3D CRT techniques and are structured so that at first the dose distributions for single beams are checked, then standard multiple field techniques are used, and finally complex multi field arrangements are analyzed. The measurements are performed with either a Farmer type ionisation chamber or small

volume ionization chamber, which is placed into the proper plug and this plug is then

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inserted into a selected hole in the phantom. During the measurements all empty holes

are filled with appropriate plugs. The measurements are then performed for single beam and for multi-field techniques.

The comparison of the measured and calculated dose values uses the criteria described in TRS 430 [2]. For the evaluation of the measured and TPS calculated values the

following equation is used:

Error [%]=100*(Dcal-Dmeas)/Dmeas, ref

where Dmeas,ref is the dose value measured at the reference point. This reference point is a point that is expected to have received 2 Gy, and is specified for each test case.

To facilitate the data collection and analyses the excel file “TPS Results evaluation sheet” is provided. TPS calculated doses and electrometer readings shall be typed in and the measured dose will be then calculated according to the formalism laid out in IAEA TRS 398 [10]. The deviations will be displayed and compared with agreement criteria.

3.2.1. Anatomical and input test cases

The phantom is introduced into the TPS the same way as a patient for treatment planning.

Case 01. Verification of digitized contour – non-dosimetric test

The purpose of this test is to verify the contouring capabilities of the TPS by comparing

the digitized master copy of the CIRS 002LFC front view contour with the printed master copy, and with the correspondent contour of the CIRS 002LFC phantom created from CT images.

Compare distances A, B, C (diameter of the hole #10), D and E (cross-sections of the lung through the centres of the holes 5 and 6-7) as indicated in figure 3. The results of

these comparisons should be included into the table (Table 2). The deviation should be within 1 mm, however it should also be considered that there is a dependence on the

windowing used for contouring that may add another 1 mm.

Table 2. Comparison of the parameters of the contours.

Type of the

contour Parameters of the contours

A B C D E

Master

copy

Digitized

CT image

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Figure 3. Specification of different distances used for comparison. (image is distorted)

Case 02. Verification of HU to electron density conversion stored in the TPS

The purpose of this test is to verify, and if necessary adjust the Hounsfield units (HU) to electron density conversion curve stored in the TPS. The acceptance criterion for the

difference between CT numbers for the same relative electron density is ± 20 HU. The phantom CIRS 002LFC should be scanned in the available local CT scanner with the

following parameters: HEAD FIRST SUPINE (considering as HEAD the film section slab part of the phantom), use the kV, reconstruction algorithm, FoV, slice thickness and

spacing as usually applied in the department. The labelling of the holes and recommended arrangement of the calibrated electron density reference plugs during CT

scan is given in figure 2. For each selected inhomogeneity, water and air the HU values should be averaged over a fixed area (radius of 5-15 mm). The region of interest for

which the HU values are averaged should not be close to the edge of the selected area. The averaged values should be compared to the HU values used in HU to ED conversion

curve stored in the TPS.

The second scan of the phantom that will be used for dosimetry tests calculations should

be done with all plugs inserted into the appropriate holes using the same scanning

parameters as before.

3.2.2. Dosimetric test cases

The purpose of each dosimetric test case is described below. Generally one dosimetric test case checks several parameters. The centres of 10 holes of the phantom are defined

and their coordinates are stored in TPS. A detailed instruction for performing the testing and evaluating the results is given below.

B

A

10 C

6

7

5

D

E

10

Case 1: Confirmation of the basic beam data based on CT data

The purpose of this test is to verify the TPS calculation for the reference field, based on electron densities converted from CT data. A 10 cm x 10 cm field with a gantry angle of 0° and collimator angle of 0° is used to confirm the basic beam data. The measurement points are defined in the middle of holes 3, 9 and 10 (Table 3).

Table 3. Geometry for test case 1

Case Number

of

beams

Set up:

Aiming

point

Reference

point

Measurement

point

Field Size

W x L [cm2]

Gantry

angle

Collimator

angle

Beam

modifiers

1 1 SSD

100 cm

(linac)

80 cm

(Co-60)

5

3 3

9

10

10x10 0 0 none

Setup Instructions:

1. Align the phantom and the lasers’ intersection at the center of hole #5. 2. Set gantry angle to 0º.

3. Set SSD=100 cm (80 cm for Co-60). 4. Set collimator rotation to 0º. 5. Set field size: Width (X) = 10 cm; Length (Y) = 10 cm 6. Insert ionization chamber into the tissue plug and place it into hole #3.

7. Perform the corresponding plan on TPS and document it. 8. Calculate with TPS MU/time needed to deliver 2 Gy to the reference point (#3). 9. Perform a manual check of the TPS calculated MU. 10. Irradiate the phantom with the selected MU/time.

11. Register the value of the measured dose. Repeat irradiation at least three times and determine average value.

12. Change the position of the ionization chamber to the next hole (#9). 13. Repeat steps 10 and 11 after changing the position of the chamber.

14. Change the position of the ionization chamber to the next hole (#10). 15. Repeat steps 10 and 11 after changing the position of the chamber. 16. Fill in TPS results evaluation sheet (excel file) with calculated and measured data and compare results.

If several algorithms are available for dose calculations provide calculated values for each employed algorithm.

Case 2: Oblique incidence, lack of scattering and tangential field

The purpose of this test is to verify calculations for the tangential field where partial lack of scattering occurs. A 10 cm x 15 cm field with a wedge and a gantry angle of 90° and collimator angle depending on the wedge insertion is used. The measurement point is

defined as the middle of hole #1 (Table 4).

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Table 4. Geometry for test case #2 – SAD setup

Case Number

of beams

Set up:

Aiming

point

Reference

point

Measurement

point

Field Size

W x L

[cm2]

Gantry

angle

Collimator

angle

Beam

modifiers

2 1 SAD

1

1 1 10x15 90 depend

on w edge

insertion

45 degree

w edge

Setup Instructions:

1. Align the phantom and the lasers’ intersection at the center of hole #1. 2. Set gantry angle to 0º, distance to the phantom surface should be SAD -

d(point 1)=97 cm. 3. Set collimator rotation to 0º (collimator angle may be changed due to the conditions of

wedge insertion). 4. Set field size: Width (X) = 10 cm(wedged direction); Length (Y) = 15 cm

5. Move gantry to 90º. Insert 45º wedge, if needed rotate collimator. 6. Insert ionization chamber into the tissue plug and place it into hole #1. 7. Calculate with TPS MU/time needed to deliver 2 Gy to the reference point (1). 8. Perform a manual check of the TPS calculated MU/time

9. Irradiate the phantom with the selected MU/time. 10. Register the value of the measured dose. Repeat irradiation at least three times and

determine average value. 11. Perform the corresponding plan at TPS and document it.

12. Fill in TPS results evaluation sheet (excel file) with calculated and measured data and compare results.


Case 3: Significant blocking of the field corners

The purpose of this test is to verify the TPS calculation for the blocked field: a 14 x 14 cm2

field with a collimator angle of 45° is blocked to a 10 x 10 cm2 field using standard blocks or the MLC. The measurement point is defined in the middle of the hole #3 (Table 5).

Table 5. Geometry for test case #3

Case Number

of beams

Set up:

Aiming

point

Reference

point

Measurement

point

Field Size

W x L

[cm2]

Gantry

angle

Collimator

angle

Beam

modifiers

3 1 SSD

5

3 3 14x14

shaped

to 10x10

0 45 Blocks

or MLC

Setup Instructions:

1. Align the phantom and the lasers’ intersection at the center of hole #5.

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2. Set gantry angle to 0º.

3. Set collimator rotation to 45º. 4. Set field size: Width (X) = 14 cm; Length (Y) = 14 cm 5. Block the field corners to 10 x 10 cm2. 6. Insert ionization chamber into the tissue plug and place it into hole #3.

7. Calculate with TPS MU/time needed to deliver 2 Gy to the reference point (#3). 8. Perform a manual check of the TPS calculated MU 9. Irradiate the phantom with the selected MU/time. 10. Register the value of the measured dose. Repeat irradiation at least three times and

determine average value. 11. Perform the corresponding plan at TPS and document it. 12. Fill in TPS results evaluation sheet (excel file) with calculated and measured data and compare results.


Case 4: Four field box

This technique is used in many radiotherapy centres and the purpose of this test is to verify the TPS calculation of the dose delivered by individual beams and the total dose from four fields. Four fields are weighted equally and the parameters and measurement points are defined in the middle of the holes 5, 6 and 10 (Table 6).

Table 6. Geometry for test case #4.

Case Number of

beams

Set up:

Aiming

point

Reference

point

Measurement

point

Field Size

W x L

[cm2]

Gantry

angle

Collimator

angle

Beam

modifiers

4 4 SAD

5

5 5

6

10

10x15

Ant

8x15 RL

10x15

Post

8x15 LL

0

90

180

270

0

0

0

0

none

Setup Instructions:

1. Align the phantom and the lasers’ intersection at the center of hole #5. 2. Set gantry angle to 0º. 3. Set collimator rotation to 0º. 4. Set field size: Width (X) = 10 cm; Length (Y) = 15 cm

5. Insert ionization chamber into the tissue plug and place it into hole #5. 6. Calculate with TPS MU/time needed to deliver 2 Gy to the reference point (5) from all four fields. 7. Perform a manual check of the TPS calculated MU/time for each field

8. Irradiate the phantom with the selected MU/time for anterior field only. 9. Register the value of the measured dose. Repeat irradiation at least three times and determine average value. 10. Rotate gantry to 90º.

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11. Set field size: Width (X) = 8 cm; Length (Y) = 15 cm

12. Irradiate the phantom with the selected MU/time for left lateral field. 13. Register the value of the measured dose. Repeat irradiation at least three times and determine average value. 14. Rotate gantry to 180º.

15. Set field size: Width (X) = 10 cm; Length (Y) = 15 cm 16. Irradiate the phantom with the selected MU/time for posterior field. 17. Register the value of the measured dose. Repeat irradiation at least three times and determine average value.

18. Rotate gantry to 270º. 19. Set field size: Width (X) = 8 cm; Length (Y) = 15 cm 20. Irradiate the phantom with the selected MU/time for right lateral field. 21. Register the value of the measured dose. Repeat irradiation at least three times and

determine average value. 22. Insert ionization chamber into the lung equivalent plug and place it into hole #6. 23. Repeat steps 2-21 (except step 7) with the ionization chamber placed in hole #6. 24. Insert ionization chamber into the bone equivalent plug and place it into hole #10.

25. Repeat steps 2-21 (except step 7) with the ionization chamber placed in hole #10. 26. Perform the corresponding plan at TPS and document it. 27. Fill in TPS results evaluation sheet (excel file) with calculated and measured data and compare results.


Case 5: Customized blocking

The purpose of this test is to verify auto-aperture function and customized blocking as well as the TPS calculations utilizing lung inhomogeneity corrections. A 8 cm diameter and 8 cm long cylinder centered in point #2 should be expanded with a margin of 1 cm in all directions using the expansion tools available. An MLC or block should be used to

conform the field to expanded volume. The measurement points are defined as the middle of holes # 2 and #7 (Table 7).


Case Number

of

beams

Set up:

Aiming

point

Reference

point

Measurement

point

Field Size

W x L

[cm2]

Gantry

angle

Collimator

angle

Beam

modifiers

5 1 SAD

2

2 2

7

12x12 or

auto

defined

0 0 Custom

block

Setup Instructions:

1. Align the phantom and the lasers’ intersection at the center of hole #5.

2. Set gantry angle to 0º. 3. Move the table laterally 4 cm (isocenter at the hole #2). 4. Set collimator rotation to 0º. 5. Set field size: Width (X) = 12 cm; Length (Y) = 12 cm or as automatically defined

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6. Insert ionization chamber into the tissue plug and place it into hole #2.

7. Calculate with TPS MU/time needed to deliver 2 Gy to the reference point (2). 8. Perform a manual check of the TPS calculated MU 9. Insert custom block. 10. Irradiate the phantom with the selected MU/time.

11. Register the value of the measured dose. Repeat irradiation at least three times and determine average value. 12. Insert ionization chamber into the lung equivalent plug and place it into hole #7. 13. Follow steps 10-11.

14. Perform the corresponding plan at TPS and document it. 15. Fill in TPS results evaluation sheet (excel file) with calculated and measured data and compare results.


Case 6: L shaped field with oblique incidence

The purpose of this test is to verify the TPS calculations for irregular fields with the

blocking of the centre of the field. A 10 cm x 20 cm field with gantry angle of 45° and collimator angle of 0° is used. An L-shaped field should be created by blocking off a 6 x 12 cm2 field using custom blocks or MLC. The parameters and measurement points are defined in the middle of the holes 3, 7, and 10 (Table 8).


Case Number

of

beams

Set up:

Aiming

point

Reference

point

Measurement

point

Field Size

W x L

[cm2]

Gantry

angle

Collimator

angle

Beam

modifiers

6 1 SAD

5

3 3

7

10

L-shaped

10x20

45 0 Custom

block or

MLC

Setup Instructions:

1. Align the phantom and the lasers’ intersection at the center of hole #5. 2. Set gantry angle to 45º. 3. Set collimator rotation to 0º.

4. Set field size: Width (X) = 10 cm; Length (Y) = 20 cm 5. Insert ionization chamber into the tissue plug and place it into hole #3. 6. Calculate with TPS MU/time needed to deliver 2 Gy to the reference point (3). 7. Perform a manual check of the TPS calculated MU

8. Insert custom block or shape the field with the MLC. 9. Irradiate the phantom with the selected MU/time. 10. Register the value of the measured dose. Repeat irradiation at least three times and determine average value. 11. Move ionization chamber with the tissue plug into hole #7.

12. Irradiate the phantom with the selected MU/time. 13. Insert ionization chamber into the lung equivalent plug and place it into hole #10.

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14. Irradiate the phantom with the selected MU/time.

15. Register the value of the measured dose. Repeat irradiation at least three times and determine average value. 16. Perform the corresponding plan at TPS and document it. 17. Fill in TPS results evaluation sheet (excel file) with calculated and measured data and

compare results.

If several algorithms are available for dose calculations provide calculated values for each

employed algorithm.

Case 7. Three field plan with asymmetrical fields and wedges.

The purpose of this test is to verify the TPS calculations with wedge-paired fields and asymmetric collimation (if asymmetric collimators are not available – use half-beam block). All fields are equally weighted. The isocenter is set in the center of the hole #3.

Collimator angle should be set following wedges insertion. The parameters and measurement points are defined in the middle of hole 5 (Table 9).


Case Number of

beams

Set up:

Aiming

point

Reference

point

Measurement

point

Field Size

W x L [cm 2]

Gantry

angle

Collimator

angle

Beam

modifiers

7 3 SAD

3

3 5 12x10

6assym x10

6assym x10

0

100

260

0

Depend on

w edge

insertion

None

Wedge 30

Wedge 30

Setup Instructions:

1. Align the phantom and the lasers’ intersection at the center of hole #3. 2. Set gantry angle to 0º. 3. Set collimator rotation to 0º. 4. Set field size: Width (X) = 12 cm; Length (Y) = 10 cm

5. Insert ionization chamber into the tissue plug and place it into hole #5. 6. Calculate with TPS MU/time needed to deliver 2 Gy to the reference point (3) for each field. 7. Perform a manual check of the TPS calculated MU for all three beams

8. Irradiate the phantom with the selected MU/time for anterior field. 9. Register the value of the measured dose. Repeat irradiation at least three times and determine average value. 10. Rotate gantry to 100º.

11. Set collimator rotation angle to enable proper wedge insertion. 12. Set field size: Width (X1) = 0, Width (X2) = 6cm; Length (Y) = 10 cm (those who do not have asymmetric jaws use on this field half beam block and set the field size to 10x12 cm2)

13. Insert 30 degrees wedge. 14. Irradiate the phantom with the selected MU/time for LL field. 15. Register the value of the measured dose. Repeat irradiation at least three times and determine average value.

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16. Rotate gantry to 260º.

17. Set collimator rotation angle to enable proper wedge insertion. 18. Use soft wedge, if available. 19. Irradiate the phantom with the selected MU/time for RL field. 20. Register the value of the measured dose. Repeat irradiation at least three times and

determine average value. 21. Perform the corresponding plan on the TPS and document it. 22. Fill in TPS results evaluation sheet (excel file) with calculated and measured data and compare results.


Case 8. Plan with non-coplanar field.

The purpose of this test is to verify the TPS calculations with couch and collimator rotations. Three fields with different gantry angles and collimator rotations are equally weighted. The isocentre is set in the centre of hole #5. The parameters and measurement point are defined in the middle of the hole #5 (Table 10).


Case Number

of beams

Set up:

Aiming

point

Reference

point

Measurement

point

Field Size

W x L [cm 2]

Gantry

angle

Collimator

angle

Beam

modifiers

8 3 SAD

5

5 5 4x4

(table 270)

4x16 LL

4x16 RL

30

90

270

0

60

300

None

Setup Instructions:

1. Align the phantom and the lasers’ intersection at the center of hole #5. 2. Set gantry angle to 0º.

3. Set collimator rotation to 0º. 4. Rotate table isocentrically to 270º. 5. Set field size: Width (X) = 4 cm; Length (Y) = 4 cm 6. Insert ionization chamber into the tissue plug and place it into hole #5.

7. Calculate with TPS MU/time needed to deliver 2 Gy to the reference point (5) for all fields. 8. Perform a manual check of the TPS calculated MU/time for all fields. 9. Irradiate the phantom with the selected MU/time for non coplanar field.

10. Register the value of the measured dose. Repeat irradiation at least three times and determine average value. 11. Set gantry angle to 90º. 12. Set collimator rotation to 60º.

13. Set field size: Width (X) = 4 cm; Length (Y) = 16 cm 14. Irradiate the phantom with the selected MU/time for LL field.

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15. Register the value of the measured dose. Repeat irradiation at least three times and

determine average value. 16. Set gantry angle to 270º. 17. Set collimator rotation to 300º. 18. Irradiate the phantom with the selected MU/time for RL field.

19. Register the value of the measured dose. Repeat irradiation at least three times and determine average value. 20. Perform the corresponding plan at TPS and document it. 21. Fill in TPS results evaluation sheet (excel file) with calculated and measured data and

compare results.


employed algorithm.

If time allows the following additional tests could be performed :

Case 1A: Large field (optional test)

The purpose of this test is to verify the TPS calculation for the large field, based on

electron densities derived from converted CT data. A 25 cm x 25 cm2 field with a gantry angle of 0° and collimator angle of 0° is used. The measurement points are defined in the middle of holes 3 and 7 (table 11).

Table 11. Geometry for test case 1A

Case Number

of

beams

Set up:

Aiming

point

Reference

point

Measurement

point

Field Size

W x L [cm2]

Gantry

angle

Collimator

angle

Beam

modifiers

1A 1 SSD

100 cm

(linac)

80 cm

(Co-60)

5

3 3

7

25x25 0 0 none

Setup Instructions:

1. Align the phantom and the lasers’ intersection at the center of hole #5. 2. Set gantry angle to 0º. 3. Set SSD= 100 cm (80 cm for Co-60).

4. Set collimator rotation to 90º. 5. Set field size: Width (X) = 25 cm; Length (Y) = 25 cm 6. Insert ionization chamber into the tissue plug and place it into hole #3. 7. Perform the corresponding plan at TPS and document it.

8. Calculate with TPS MU/time needed to deliver 2 Gy to the reference point (#3). 9. Perform a manual check of the TPS calculated MU. 10. Irradiate the phantom with the selected MU/time. 11. Register the value of the measured dose. Repeat irradiation at least three times and

determine average value. 12. Change the position of the ionization chamber to the next hole (#7). 13. Repeat steps 10 and 11 after changing the position of the chamber.

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14. Fill in TPS results evaluation sheet (excel file) with calculated and measured data and

compare results. Agreement criteria for point 3 and 7 is 2% and 3%, respectively.


employed algorithm.

Case 1B: Extended SSD (optional test)

The purpose of this test is to verify the TPS calculation for a small field at extended SSD. A 4 cm x 4 cm field with a gantry angle of 0° and collimator angle of 90° is used. The

measurement points are defined in the middle of hole 3 (table 12).

Table 12. Geometry for test case 1B

Case Number

of

beams

Set up:

Aiming

point

Reference

point

Measurement

point

Field Size

W x L [cm2]

Gantry

angle

Collimator

angle

Beam

modifiers

1B 1 SSD

125 cm (linac)

100 cm

(Co-60)

3 3

4x4 0 0 none

Setup Instructions:

1. Align the phantom with lasers intersection at the center of the hole #5. 2. Set gantry angle to 0º. 3. Set SSD=125 cm (100 cm for Co-60). 4. Set collimator rotation to 90º.

5. Set field size: Width (X) = 4 cm Length (Y) = 4 cm 6. Insert ionization chamber into the tissue plug and place it into hole #3. 7. Perform the corresponding plan at TPS and document it. 8. Calculate with TPS MU/time needed to deliver 2 Gy to the reference point (#3).

9. Perform a manual check of theTPS calculated MU. 10. Irradiate the phantom with the selected MU/time. 11. Register the value of the measured dose. Repeat irradiation at least three times and

determine average value.

12. Fill in TPS results evaluation sheet (excel file) with calculated and measured data and compare results. Agreement criteria for point 3 is 2%.


19

REFERENCES

[1]. IAEA Safety Report Series #17 “Lessons learned from accidental exposures in radiotherapy” 2000.

[2]. IAEA TECDOC 1583 “Clinical Commissioning Protocol for Radiotherapy Treatment Planning Systems” 2008.

[3]. IAEA Technical Report Series #430 ”Commissioning and Quality Assurance of Computerized Planning Systems for Radiation Treatment of Cancer” 2004.

[4]. KUTCHER GJ, et al., Report of AAPM TG 40, Comprehensive QA for radiation oncology, Med. Phys. 21, 581-618, (1994)

[5]. THWAITES, D.I., SCALLIET, P., LEER, J.W., OVERGAARD, J., Quality Assurance in Radiotherapy, Radiother. Oncol. 35 61–73 (1995)

[6]. LEER JW, MCKENZIE A, SCALLIET P, AND THWAITES DI, Practical guidelines for the implementation of a quality system in radiotherapy, ESTRO Physics for Clinical Radiotherapy booklet no. 4, ESTRO, Brussels, (1998)

[7]. IZEWSKA J, SVENSSON H, IBBOTT G, Worldwide Quality Assurance networks for radiotherapy dosimetry, Proceedings of the International Symposium on Standards and Codes of Practice in Medical Radiation

Dosimetry, 25-28 November 2002, Vienna, IAEA-CN-96/76, 139-155, Vienna (2004)

[8]. IZEWSKA J, ANDREO P, The IAEA/WHO TLD postal programme for radiotherapy hospitals, Radiother. Oncol., 54 65-72 (2000)

[9]. INTERNATIONAL ATOMIC ENERGY AGENCY, Standardized quality audit procedures for on-site dosimetry review visits to radiotherapy hospitals, Izewska J. et al., SSDL Newsletter No.46, Vienna (2002)

[10]. IAEA Technical Report Series #398 ” Absorbed Dose Determination in External Beam Radiotherapy. An International Code of Practice for Dosimetry Based on Standards of Absorbed Dose to Water” 2001.

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APPENDIX 1: QUESTIONNAIRE/ REQUEST FOR AUDIT

1. Name of the hospital:

2. Address:

3. Number of patients treated with external beam radiotherapy per year:

2D RT: 3D CRT: IMRT:

4. Number of external beam treatment units:

5. Make, models and beams of treatment units where the measurements will be performed:

6. Make and version of TPS to be audited:

7. Clinically used algorithms:

8. Location of CT scanner:

Diagnostic Radiology Dpt. Radiotherapy Dpt. Other

9. Make and model of CT scanner used for RT:

10. Dosimetry equipment:

Electrometer:

Chamber:

Calibrated by: Date:

11. Previous participation in external audits: Yes No

12. If yes,

Type of audit: Auditor: Date:

13. The preferred time for TPS audit:

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APPENDIX 2: ON SITE QUESTIONNAIRE

1. Name of the hospital:

2. Make and version of TPS:

3. Commissioning date:

4. Calculation model is based on:

Hospital measured data Generic beam data

5. Beam modelling was performed by:

User Vendor

6. Calculation grid size used for test calculations:

10. Is it differs from clinically used?:

Yes No

7. Inhomogeneity correction method:

pixel by pixel bulk densities No correction

8. If, pixel by pixel inhomogeneity corrections is being used, Hounsfield Units to relative

electron density conversion (HU to RED) is based on:

Hospital measured data Generic data

9. If hospital uses several CT scanners or several scanning protocols, does it use:

HU to RED for each scanner or protocol average HU to RED Other

10. CT used for 3D-CRT equipped with flat table top:

Yes No

11. Data transfer from TPS to accelerator:

Electronic Manual

12. Independent MU calculation is performed:

Manually Using computer program Another TPS Not performed

13. Comments:

dosimetric audit of treatment planning systems...treatment planning and delivery processes. the...

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