rt06 brachy1 sources web

8/8/2019 RT06 Brachy1 Sources WEB

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Radiation Protection inRadiation Protection inRadiotherapyRadiotherapy

Part 6Part 6

Properties and safety of radiotherapyProperties and safety of radiotherapy

sources and equipment used forsources and equipment used for

brachytherapybrachytherapy

IAEA Training Material on Radiation Protection in Radiotherapy


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Radiation Protection in Radiotherapy Part 6, lecture 1: Brachytherapy sources 2

BrachytherapyBrachytherapy

Breast implant using

radioactive 192-Ir wire

The use of radioactive sources in closeThe use of radioactive sources in close

proximity to the target area for radiotherapyproximity to the target area for radiotherapy

X Ray of a gynaecological

implant using an applicatorloaded with 137-Cs sources


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Brachytherapy overviewBrachytherapy overview Brachytherapy uses encapsulatedBrachytherapy uses encapsulated

radioactive sources to deliver a highradioactive sources to deliver a high

dose to tissues near the sourcedose to tissues near the source brachys (Greek) = short (distance)brachys (Greek) = short (distance)

Inverse square law determines most ofInverse square law determines most of

the dose distributionthe dose distribution


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BrachytherapyBrachytherapy Characterized by strongCharacterized by strong

dose gradientsdose gradients

Many different techniquesMany different techniquesand sources availableand sources available

Implants are highlyImplants are highly

customized for individualcustomized for individualpatientspatients


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BrachytherapyBrachytherapy Use of radioactive materials in direct contactUse of radioactive materials in direct contact

with patientswith patients -- more radiation safety issuesmore radiation safety issues

than in external beam radiotherapythan in external beam radiotherapy

Less than 10% of radiotherapy patients areLess than 10% of radiotherapy patients are

treated with brachytherapytreated with brachytherapy

Per patient treated the number of accidents inPer patient treated the number of accidents in

brachytherapy is considerably higher than inbrachytherapy is considerably higher than inEBTEBT


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Objectives of part 6Objectives of part 6

To be familiar with typical radioactive sources used inTo be familiar with typical radioactive sources used in

cancer treatmentcancer treatment

To be aware of different implant types andTo be aware of different implant types and

techniquestechniques To appreciate the implications of life implantsTo appreciate the implications of life implants vs.vs.

manual and remote afterloadingmanual and remote afterloading

To understand the differences between low and highTo understand the differences between low and high

dose rate brachytherapy equipmentdose rate brachytherapy equipment To be familiar with some special current implantTo be familiar with some special current implant

techniques (prostate seed implants, endovasculartechniques (prostate seed implants, endovascular

brachytherapy)brachytherapy)


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ContentsContents Lecture 1: Brachytherapy Sources andLecture 1: Brachytherapy Sources and

equipmentequipment

Lecture 2: Brachytherapy techniquesLecture 2: Brachytherapy techniques

(including special techniques such as(including special techniques such as

prostate seed implants andprostate seed implants and

endovascular brachytherapy)endovascular brachytherapy)


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Flow of brachytherapyFlow of brachytherapy

information in the courseinformation in the coursePart 2: Physics

Part 6: Brachytherapy (Description of techniques and

equipment)

Part 11: Good practice in brachytherapy (Information

placed in context of BSS with emphasis on radiation

protection)

Parts 14 (Transport), 15 (Security of sources) and 16

(Discharge of patients): Additional and supporting

information - most of it directly relevant for

brachytherapy practice


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Radiation Protection inRadiation Protection inRadiotherapyRadiotherapy

Part 6Part 6

BrachytherapyBrachytherapyLecture 1: Brachytherapy Sources and EquipmentLecture 1: Brachytherapy Sources and Equipment

IAEA Training Material on Radiation Protection in Radiotherapy


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ObjectivesObjectives To understand the concept of sealed sourceTo understand the concept of sealed source

To know the most common isotopes used forTo know the most common isotopes used for


To be familiar with general rules for source handlingTo be familiar with general rules for source handling

and testingand testing

To be aware of differences between permanentTo be aware of differences between permanent

implants, low (LDR) and high dose rate (HDR)implants, low (LDR) and high dose rate (HDR)

applicationsapplications To understand the basic fundamentals ofTo understand the basic fundamentals of

brachytherapy equipment designbrachytherapy equipment design


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ContentsContents1 Sealed sources1 Sealed sources

2 The ideal source for radiotherapy2 The ideal source for radiotherapy

3 Brachytherapy sources in use3 Brachytherapy sources in use


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HenriHenri

BecquerelBecquerel

(1852(1852--1908)1908)

Discovered radioactivity in 1896


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1. Sealed sources1. Sealed sources

IAEA BSS glossary: RadioactiveIAEA BSS glossary: Radioactive

material that is a) permanently sealed inmaterial that is a) permanently sealed in

a capsule or b) closely bound and in aa capsule or b) closely bound and in asolid form.solid form.

In other words: the activity is fixed to itsIn other words: the activity is fixed to its

carrier and contamination of thecarrier and contamination of theenvironment is not possible as long asenvironment is not possible as long as

the source is intactthe source is intact


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Sealed sourcesSealed sources

Have an activity which can be derivedHave an activity which can be derived

from a calibration certificate and the halffrom a calibration certificate and the half

life of the isotope (nothing is lost)life of the isotope (nothing is lost)

MUST be checked for integrity regularlyMUST be checked for integrity regularly

-- a good means of doing this is by wipea good means of doing this is by wipe

teststests


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Sealed and unsealed sources inSealed and unsealed sources in

radiotherapyradiotherapy Both are used to treat cancerBoth are used to treat cancer

Sealed sources are used forSealed sources are used for

brachytherapybrachytherapy -- they are discussed herethey are discussed here

Unsealed sources may be used forUnsealed sources may be used for

systemic treatmentssystemic treatments -- they arethey are

discussed in more detail in the coursediscussed in more detail in the courseon Nuclear Medicineon Nuclear Medicine


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Some examples for unsealedSome examples for unsealed

source radiotherapysource radiotherapy 131131--I for thyroid treatmentI for thyroid treatment

8989--Sr and 153Sr and 153--Sm for treatment of boneSm for treatment of bone

metastasismetastasis

3232--P for hematological cancersP for hematological cancers


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NoteNote

All brachytherapy sources are of anAll brachytherapy sources are of an

activity which makes them of regulatoryactivity which makes them of regulatory

concernconcern

Therefore, persons ordering, receiving,Therefore, persons ordering, receiving,

handling, storing and disposing themhandling, storing and disposing them

must have appropriate training and holdmust have appropriate training and holdthe appropriate licensethe appropriate license


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2. The ideal source in2. The ideal source in


What do you think one would expect fromWhat do you think one would expect from

and ideal brachytherapy source?and ideal brachytherapy source?


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Clinical usefulness determined byClinical usefulness determined by

Half lifeHalf life = the time after which half of the= the time after which half of the

original activity is still present in the sourceoriginal activity is still present in the source

Specific activitySpecific activity = activity per gram of= activity per gram of

material. The higher the specific activity, thematerial. The higher the specific activity, thesmaller a source of a particular activity can besmaller a source of a particular activity can be

mademade

Radiation energyRadiation energy determines the range ofdetermines the range of

radiation in tissue (AND the requirements forradiation in tissue (AND the requirements for

shielding)shielding)


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The Ideal Brachytherapy sourceThe Ideal Brachytherapy source

Pure gamma emitterPure gamma emitter -- betas or alphas are toobetas or alphas are too

short in range and result in very high doses toshort in range and result in very high doses to

small volumes around the sourcesmall volumes around the source

Medium gamma energyMedium gamma energy high enough to treat the target with homogenoushigh enough to treat the target with homogenous

dosedose

low enough to avoid normal tissues and reducelow enough to avoid normal tissues and reduce

shielding requirementsshielding requirements

High specific activityHigh specific activity

suitable also for high dose rate applicationssuitable also for high dose rate applications

smallsmall


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The Ideal Brachytherapy sourceThe Ideal Brachytherapy source

Stable daughter productStable daughter product

For temporary implants: long half lifeFor temporary implants: long half life

allows economical reallows economical re--use of sourcesuse of sources For permanent implants: medium halfFor permanent implants: medium half

lifelife


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3. Real brachytherapy Sources3. Real brachytherapy Sources

A variety of source types and isotopes areA variety of source types and isotopes are

currently in usecurrently in use

They differ for different applications becauseThey differ for different applications because

ofof half life,half life,

size (specific activity) andsize (specific activity) and

radiation energyradiation energy

When deciding on a source one must alsoWhen deciding on a source one must also

keep the shielding requirements in mindkeep the shielding requirements in mind


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Brachytherapy SourcesBrachytherapy SourcesRadionuclide Half-life Photon Energy (MeV) Half-value Layer (mm lead)

226Ra 1600 years 0.047 - 2.45 (0.83 ave) 8.0

222Rn 3.83 days 0.047 - 2.45 (0.83 ave) 8.0

60Co 5.26 years 1.17, 1.33 11.0137

Cs 30.0 years 0.662 5.5

192Ir 74.2 days 0.136 - 1.06 (0.38 ave) 2.5

198Au 2.7 days 0.412 2.5

125

I 60.2 days 0.028 ave 0.025103

Pd 17.0 days 0.021 ave 0.008


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BrachytherapyBrachytherapy

source typessource types(ICRU report(ICRU report

58)58)


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Brachytherapy sourcesBrachytherapy sources

The first isotope used clinically was radiumThe first isotope used clinically was radium

around 1903around 1903


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Brachytherapy sourcesBrachytherapy sources

However, radium and radon have onlyHowever, radium and radon have only

historical importancehistorical importance -- they should not be usedthey should not be used

in a modern radiotherapy departmentin a modern radiotherapy department

Because:Because: wide energy spectrum leading to high dose close towide energy spectrum leading to high dose close to

the source and still high dose around the patientthe source and still high dose around the patient --

shielding difficultshielding difficult

Radon, the daughter product of radium, is a nobleRadon, the daughter product of radium, is a noblegas which is very difficult to containgas which is very difficult to contain -- contaminationcontamination

riskrisk

The long half life means disposal is very difficultThe long half life means disposal is very difficult


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Popular sources: 137Popular sources: 137--CsCs

Cesium 137Cesium 137

Main substitute for radiumMain substitute for radium

Mostly used in gynecologicalMostly used in gynecological

applicationsapplications

Long half life of 30 yearsLong half life of 30 years ------> decay> decay

correction necessary every 6 monthscorrection necessary every 6 months Sources are expensive and must beSources are expensive and must be

replaced every 10 to 15 yearsreplaced every 10 to 15 years


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Popular sources: 192Popular sources: 192--IrIr

Iridium 192Iridium 192

Many different forms availableMany different forms available

Most important source for HDR applicationsMost important source for HDR applications Medium half life (75 days)Medium half life (75 days) -- decay correctiondecay correction

necessary for each treatmentnecessary for each treatment

Needs to be replaced every 3 to 4 months toNeeds to be replaced every 3 to 4 months to

maintain effective activity and therefore anmaintain effective activity and therefore anacceptable treatment timeacceptable treatment time


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Popular sources: 192Popular sources: 192--IrIr

Iridium 192Iridium 192

High specific activityHigh specific activity -- therefore even hightherefore even high

activity sources can be miniaturized essentialactivity sources can be miniaturized essential

for HDR applicationsfor HDR applications

A bit easier to shield than 137A bit easier to shield than 137--CsCs -- becausebecause

the gamma energies of 192the gamma energies of 192--Ir range from 136Ir range from 136

to 1062keV (effective energy around 350keV)to 1062keV (effective energy around 350keV)


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HDR 192HDR 192--Ir sourceIr source

10 Ci (370GBq)10 Ci (370GBq)

diameter of the order of 1mmdiameter of the order of 1mm

length of the order of 10mmlength of the order of 10mm dual encapsulationdual encapsulation

attached to steel cableattached to steel cable


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HDR source: anisotropy ofHDR source: anisotropy of

dosedose


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Popular sources: 125Popular sources: 125--II

Very low energyVery low energy -- therefore shielding istherefore shielding is

easy and radiation from an implant iseasy and radiation from an implant is

easily absorbed in the patient:easily absorbed in the patient:permanent implants are possiblepermanent implants are possible

Mostly used in theMostly used in the

form of seedsform of seeds


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125125--I seedsI seeds

Many different designsMany different designs


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Design aims andDesign aims and

features:features:

sealed sourcesealed source nonnon--toxic tissuetoxic tissue

compatible encapsulationcompatible encapsulation

isotropic dose distributionisotropic dose distribution

radioradio--opaque foropaque forlocalizationlocalization

Mentor


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X Ray visibility of 125X Ray visibility of 125--I seedsI seeds


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A different design:A different design:

radioradio--opaque for X Rayopaque for X Ray

visualizationvisualization MRI compatibilityMRI compatibility

desirabledesirable

No contaminationNo contamination

A source example


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Symmetry of dose distributionSymmetry of dose distribution


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Other isotopes used for seedsOther isotopes used for seeds

Gold 198Gold 198

Half Life = 2.7 daysHalf Life = 2.7 days --

short enough to letshort enough to letactivity decay in theactivity decay in the

patientpatient

Energy = 412 keVEnergy = 412 keV

TVL lead = aroundTVL lead = around

8mm8mm

Palladium 103Palladium 103

Half Life = 17 daysHalf Life = 17 days --

dose rate about 2.5dose rate about 2.5times larger than fortimes larger than for

125125--II

Energy = 22 keVEnergy = 22 keV

TVL lead = 0.05mmTVL lead = 0.05mm


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Brachytherapy SourcesBrachytherapy SourcesA variety of source shapes and forms:A variety of source shapes and forms:

pellets = balls of approximately 3 mm diameter

seeds = small cylinders about 1 mm diameter and 4 mm

length

needles = between 15 and 45 mm active length tubes = about 14 mm length, used for gynaecological

implants

hairpins = shaped as hairpins, approximately 60 mm active

length

wire = any length, usually customised in the hospital -inactive ends may be added

HDR sources = high activity miniature cylinder sources

approximately 1mm diameter, 10mm length


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Source form examplesSource form examples

Seeds (discussed before):Seeds (discussed before): small containers for activitysmall containers for activity

usually 125usually 125--I, 103I, 103--Pd or 198Pd or 198--Au for permanentAu for permanent

implant such as prostate cancerimplant such as prostate cancer

Needles and hairpins:Needles and hairpins: for life implants in the operating theatrefor life implants in the operating theatre -- activityactivity

is directly introduced in the target region of theis directly introduced in the target region of the

patientpatient

usually 192usually 192--Ir for temporary implantsIr for temporary implants e.g.e.g. of theof the

tonguetongue

Scale in mm


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Source form: 192Source form: 192--Ir wireIr wire

Used for LDR interstitial implantsUsed for LDR interstitial implants

Cut to appropriate length prior to implant toCut to appropriate length prior to implant to

suit individual patientsuit individual patient Cutting using manual technique or cutter...Cutting using manual technique or cutter...


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Source form 192Source form 192--Ir wiresIr wires

192192--Ir wire:Ir wire: activity between 0.5 andactivity between 0.5 and

10mCi per cm10mCi per cm

used for interstitialused for interstitial

implantsimplants

low to medium dose ratelow to medium dose rate

can be cut from 50 cmcan be cut from 50 cm

long coils to the desiredlong coils to the desiredlength for a particularlength for a particular

patientpatient


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Source form exampleSource form example

192192--Ir wire:Ir wire: activity between 0.5 andactivity between 0.5 and

10mCi per cm10mCi per cm

used for interstitialused for interstitial

implantsimplants

low to medium dose ratelow to medium dose rate

can be cut from 50 cmcan be cut from 50 cm

long coils to the desiredlong coils to the desiredlength for a particularlength for a particular

patientpatient


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The requirements of BSS:The requirements of BSS:

Appendix IV.8. Registrants and licensees, in specific coAppendix IV.8. Registrants and licensees, in specific co--operationoperation

with suppliers, shall ensure that the following responsibilities bewith suppliers, shall ensure that the following responsibilities be

discharged, if applicable:discharged, if applicable:

(a)(a) toto provide a well designed and constructed sourceprovide a well designed and constructed source that:that:

(i)(i) provides for protection and safety in compliance with theprovides for protection and safety in compliance with theStandards;Standards;

(ii)(ii)meets engineering, performance and functional specifications; andmeets engineering, performance and functional specifications; and

(iii)(iii) meets quality norms commensurate with the protection and safetymeets quality norms commensurate with the protection and safety

significance of components and systems;significance of components and systems;

(b)(b) toto ensure that sources be testedensure that sources be tested to demonstrateto demonstrate

compliance with the appropriate specifications; andcompliance with the appropriate specifications; and

(c)(c) toto make available informationmake available information in a major world languagein a major world language

acceptable to the user concerning the proper installation andacceptable to the user concerning the proper installation and

use of the source and its associated risks.use of the source and its associated risks.


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SummarySummary

A wide variety of radioactive sources haveA wide variety of radioactive sources have

been used for brachytherapy in manybeen used for brachytherapy in many

different physical formsdifferent physical forms

The most common sources are 137The most common sources are 137--Cs, 192Cs, 192--Ir and 125Ir and 125--II

Regular check of source integrity is essentialRegular check of source integrity is essential

to ensure the source can be classified asto ensure the source can be classified assealedsealed


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ReferencesReferences

Johns H E and Cunningham J R 1983 The Physics of

Radiology, 4th edition (Springfield: C Thomas)

Khan F M 1994 The Physics of Radiation Therapy,

2nd edition (Williams & Wilkins, Baltimore)

Williams J R and Thwaites D I 1993 Radiotherapy

Physics in Practice (Oxford: Oxford University Press)


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Any questions?Any questions?


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Question

Question

Why would people use 198Why would people use 198--Au forAu for

brachytherapy?brachytherapy?


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Some clues for an answerSome clues for an answer

Key features of 198Key features of 198--Au are:Au are:

small sources (seed)small sources (seed)

short half life (2.7 days)short half life (2.7 days)

inert materialinert material

photon energy 412keVphoton energy 412keV

Therefore, ideal for permanent implant

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