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Radiation Protection inRadiotherapy

Part 6Brachytherapy

Lecture 2: Brachytherapy Techniques

IAEA Training Material on Radiation Protection in Radiotherapy


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Radiation Protection in Radiotherapy Part 6, lecture 2: Brachytherapy techniques 2

Brachytherapy

Very flexible radiotherapy delivery

Source position determines treatment success

Depends on operator skill and experience

In principle the ultimate conformalradiotherapy

Highly individualized for each patient

Typically an inpatient procedure as opposed toexternal beam radiotherapy which is usually

administered in an outpatient setting


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Objectives

To be familiar with different implanttechniques

To be aware of differences betweenpermanent implants, low (LDR) and high

dose rate (HDR) applications

To appreciate the potential for optimization inhigh dose rate brachytherapy

To be familiar with some special techniquesused in modern brachytherapy (seed

implants, endovascular brachytherapy)


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Contents

1. Clinical brachytherapy applications

2. Implant techniques and applicators

3. Delivery modes and equipment4. Special techniques

A. Prostate seed implants

B. Endovascular brachytherapy C. Ophthalmic applicators


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Clinical brachytherapy


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History

Brachytherapy has been one of the earliestforms of radiotherapy

After discovery of radium by M Curie, radiumwas used for brachytherapy already late

19th century

There is a wide range of applications - thisversatility has been one of the mostimportant features of brachytherapy


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Today

Many different techniques and a large

variety of equipment Less than 10% of radiotherapy patients

receive brachytherapy

Use depends very much on training andskill of clinicians and access to

operating theatre


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A brachytherapy patient

Typically localized cancer

Often relatively small tumour

Often good performance status (musttolerate the operation)

Sometimes pre-irradiated with externalbeam radiotherapy (EBT)

Often treated with combinationbrachytherapy and EBT


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Patient flow in brachytherapy

Treatment decision

Ideal plan - determines source number

and location

Implant of sources or applicators in theatre

Treatment plan

Localization of sources or applicators

(typically using X Rays)

Commence treatment


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1. Clinical brachytherapy applications

A. Surface moulds

B. Intracavitary (gynaecological, bronchus,..)

C. Interstitial (Breast, Tongue, Sarcomas, )not covered here: unsealed source

radiotherapy (Thyroid, Bone metastasis, )- this is dealt with in the IAEA trainingmaterial on radiation protection in Nuclear

Medicine


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A. Surface moulds

Treatment of superficial lesions withradioactive sources in close contact

with the skin

A mould for the back

of a hand includingshielding designed to

protect the patient

during treatment

Hand

Catheters for

source transfer


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Historical example

Surface applicator

with irregulardistribution of

radium on the

applicator surface

(Murdoch, Brussels1933)


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Other example

Treatment ofsquamous cell

carcinoma ofthe forehead

Catheters for source

placement


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Source distance from the skin

Determines incident dose

Determines dose fall off in skin - the furtherthe sources are from the skin the less

influence has dose fall off due to inverse

square law

Dose homogeneity - the further away the

sources are the more homogenous the dosedistribution is at the skin


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Simulator films of forehead mould

Dummy wires as markers for location


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Surface mould advantages

Fast dose fall off in tissues

Can conform the activity to any surface

Flaps available


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B. Intracavitary implants

Introduction of radioactivity using anapplicator placed in a body cavity

Gynaecological implants Bronchus

Oesophagus

Rectum


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Gynaecological implants

Most commonbrachytherapy application -

cervix cancer

Many different applicators

Either as monotherapy orin addition to external

beam therapy as a boost


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Gynecological applicators

Different design - all Nucletron


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Vaginal applicators

Single source line

Different diametersand length

Nucletron

Gammamed - on the right with shielding


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Bronchus implants

Often palliative to openair ways

Usually HDR

brachytherapy Most often single

catheter, however also

dual catheter possible


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Dual catheter bronchus implant

Catheter placement viabronchoscope

Bifurcation may createcomplex dosimetry


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C. Interstitial implants

Implant of needles or flexible cathetersdirectly in the target area

Breast

Head and Neck

Sarcomas

Requires surgery - often major


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Interstitial implants - tongue implant

tongue

tongue

Catheter loop

Button


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Breast implants

Typically a boost

Often utilizes templates to improve sourcepositioning

Catheters or needles


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2. Implant techniques and applicators

Permanent implants

patient discharged with implant in place

Temporary implants implant removed before patient is discharged

from hospital


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Permanent implants

Implantation of sealedsources (typically seeds) into

the target organ of the patient

Sources are NOT removedand patient is discharged with

activity in situ (compare part

16 of the course)


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Temporary implants

Implant of activity in theatre

Manual afterloading

Remote afterloading


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Implant of activity in theatre

(Common for permanent implants)

For temporary implants common practice 40years ago when radium was commonly used

for example gynecological implants of radium or137-Cs needles

Today only very rarely used for temporaryimplants - one of few examples are 192Ir

hairpins for tongue implants

Problems with handling activity in the


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Problems with handling activity in the

operating theatre

Potential of lostsources

The time to place thesources in the best

possible locations istypically limited

Radiation protection of staff mayrequire awkward operation


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Afterloading

Implant only empty applicator orneedles/catheters in theatre

Once patient has recovered, dummy sourcesare introduced to verify the location of theapplicators (typically using diagnostic X Rays)

The treatment is planned

The sources are introduced into theapplicator or needle/catheter


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Afterloading

Manual The sources are placed

manually usually by a

physicist

The sources are removedonly at the end of

treatment

Remote The sources are driven

from an intermediate

safe into the implantusing a machine(afterloader)

The sources are

withdrawn every timesomeone enters theroom


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Afterloading advantages

No rush to place the sources in theatre -more time to optimize the implant

Treatment is verified and planned prior to

delivery

Significant advantage in terms of radiationsafety (in particular if a remote afterloader is

used)


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Applicators for brachytherapy

Brachytherapy Applicators - lots to


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Brachytherapy Applicators lots tochoose from, lots to learn


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Some examples for applicators

Gynaecological applicators

Fletcher Suit

Henschke typeRing type


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Close up view


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Close-up view

Oth i t it li t


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Other intracavitary applicators

Vaginal Bronchus


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Interstitial applicators


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Interstitial applicators

Catheters flexible

open and closed end

available often introduced into

tissue via an open

end needleskin

3 D li d d i t


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3. Delivery modes and equipment

Low Dose Rate (LDR)

Medium Dose Rate (MDR)

High Dose Rate (HDR)

Pulsed Dose Rate (PDR)

Delivery modes - different


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Delivery modes differentclassifications are in use

Low Dose Rate

Medium Dose Rate

High Dose Rate

Pulsed Dose Rate

< 1Gy/hour

around 0.5Gy/hour

> 1Gy/hour

not often used >10Gy/hour

pulses of around

1Gy/hour

L d t b h th


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Low dose rate brachytherapy

The only type of brachytherapy possible withmanual afterloading

Most clinical experience available for LDR

brachytherapy

Performed with remote afterloaders using137-Cs or 192-Ir


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Treatment process


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Treatment process

Implant of applicator (typically in theoperating theatre)

Verification of applicator positioning

using diagnostic X Rays(e.g. radiotherapy simulator)

Two orthogonal views allow to localize the applicator in


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g pp

three dimensions


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HDR brachytherapy procedure


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Implant of applicators, catheters or needles in theatre For prostate implants as shown here use transrectal

ultrasound guidance



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Localization using diagnostic X Rays


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HDR it


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HDR unit

interface

HDR brachytherapy


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HDR brachytherapy

Usually fractionated (e.g. 6 fractions of 6Gy) Either patient has new implant each time or

stays in hospital for bi-daily treatments

Time between treatments should be >6hoursto allow normal tissue to repair all damage

HDR units: different designs available


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Radiation Protection in RadiotherapyPart 6, lecture 2: Brachytherapy techniques 67

HDR units: different designs available

Catheters are indexed to avoid mixing them up


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Catheters are indexed to avoid mixing them up

Transfer catheters are locked into

place during treatment - green light

indicates the catheters in use


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Pulsed dose rate


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Pulsed dose rate

Unit has a similar design as HDR, however theactivity is smaller (around 1Ci instead of 10Ci)

Stepping source operation - same optimizationpossible as in HDR

Treatment over same time as LDR treatment tomimic favorable radiobiology

In-patient treatment: hospitalization required

Source steps out for about 10 minutes per hour andthen retracts. Repeats this every hour to deliver

minifractions (pulses) of about 1Gy


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Features of PDR:


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Features of PDR:

AdvantagesEmulates LDR

Optimized dose

distribution

Visitors and

nursing staff can

use the time

between pulses

while the activity isin the safe

Disadvantages- Potential radiation safety

hazard of a source stuck in

the patient:

In LDR - low activity, no severeproblem

In HDR - physicist is present

during treatment

In PDR - will someone with

sufficient training be there within10 minutes? Even at

midnight???


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Question:

Please list advantages and disadvantages of

High Dose Rate Brachytherapy as compared to

Low Dose Rate brachytherapy. Assume both

approaches are performed using remote

afterloading equipment.


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