Radiation Protection in Radiotherapy Part 6 Brachytherapy Lecture 2: Brachytherapy Techniques IAEA Training Material on Radiation Protection in Radiotherapy

Radiation Protection inRadiotherapy

Part 6

Brachytherapy

Lecture 2: Brachytherapy Techniques

IAEA Training Material on Radiation Protection in Radiotherapy

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

Brachytherapy

• Very flexible radiotherapy delivery

• Source position determines treatment success

• Depends on operator skill and experience

• In principle the ultimate ‘conformal’ radiotherapy

• Highly individualized for each patient

• Typically an inpatient procedure as opposed to external beam radiotherapy which is usually administered in an outpatient setting


Objectives

• To be familiar with different implant techniques

• To be aware of differences between permanent implants, low (LDR) and high dose rate (HDR) applications

• To appreciate the potential for optimization in high dose rate brachytherapy

• To be familiar with some special techniques used in modern brachytherapy (seed implants, endovascular brachytherapy)


Contents

1. Clinical brachytherapy applications

2. Implant techniques and applicators

3. Delivery modes and equipment

4. Special techniques• A. Prostate seed implants

• B. Endovascular brachytherapy

• C. Ophthalmic applicators


Clinical brachytherapy


History

• Brachytherapy has been one of the earliest forms of radiotherapy

• After discovery of radium by M Curie, radium was used for brachytherapy already late 19th century

• There is a wide range of applications - this versatility has been one of the most important features of brachytherapy


Today

• Many different techniques and a large variety of equipment

• Less than 10% of radiotherapy patients receive brachytherapy

• Use depends very much on training and skill of clinicians and access to operating theatre


A brachytherapy patient

• Typically localized cancer• Often relatively small tumour• Often good performance status (must

tolerate the operation)• Sometimes pre-irradiated with external

beam radiotherapy (EBT)• Often treated with combination

brachytherapy and EBT


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


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 training material on radiation protection in Nuclear Medicine


A. Surface moulds

• Treatment of superficial lesions with radioactive sources in close contact with the skin

A mould for the back of a hand including

shielding designed to protect the patient

during treatment

Hand

Catheters for source transfer


Historical example

Surface applicator with irregular distribution of radium on the applicator surface(Murdoch, Brussels 1933)


Other example

Treatment of squamous cell carcinoma of the forehead

Catheters for source placement


Source distance from the skin

• Determines incident dose

• Determines dose fall off in skin - the further the 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 dose distribution is at the skin

Simulator films of forehead mould

Dummy wires as markers for location


Surface mould advantages

• Fast dose fall off in tissues

• Can conform the activity to any surface

• Flaps available


B. Intracavitary implants

• Introduction of radioactivity using an applicator placed in a body cavity• Gynaecological implants

• Bronchus

• Oesophagus

• Rectum


Gynaecological implants

• Most common brachytherapy application - cervix cancer

• Many different applicators

• Either as monotherapy or in addition to external beam therapy as a boost


Gynecological applicators

Different design - all Nucletron


Vaginal applicators

• Single source line

• Different diameters and length

Nucletron

Gammamed - on the right with shielding


Bronchus implants

• Often palliative to open air ways

• Usually HDR brachytherapy

• Most often single catheter, however also dual catheter possible


Dual catheter bronchus implant

• Catheter placement via bronchoscope

• Bifurcation may create complex dosimetry


C. Interstitial implants

• Implant of needles or flexible catheters directly in the target area• Breast

• Head and Neck

• Sarcomas

• Requires surgery - often major


Interstitial implants - tongue implant

tongue

tongue

Catheter loop

Button


Breast implants

• Typically a boost

• Often utilizes templates to improve source positioning

• Catheters or needles


2. Implant techniques and applicators

• Permanent implants• patient discharged with implant in place

• Temporary implants• implant removed before patient is discharged

from hospital


Permanent implants

• Implantation of sealed sources (typically seeds) into the target organ of the patient

• Sources are NOT removed and patient is discharged with activity in situ (compare part 16 of the course)


Radiation protection issues

• Patients are discharged with radioactive sources in place:• lost sources

• exposure of others

• issues with accidents to the patient, other medical procedures, death, autopsies and cremation

Discussed in more detail in parts 9 (Medical Exposure),16 (Discharge of patients) and 17 (Public exposure)


Source requirement for permanent implants

• Low energy gammas or betas to minimize radiation levels outside of the patient (125-I is a good isotope)

• May be short-lived to reduce dose with time (198-Au is a good isotope)

• More details on most common 125-I prostate implants in section 4A of the lecture


Temporary implants

• Implant of activity in theatre

• Manual afterloading

• Remote afterloading


Implant of activity in theatre

• (Common for permanent implants)

• For temporary implants common practice 40 years ago when radium was commonly used• for example gynecological implants of radium or

137-Cs needles

• Today only very rarely used for temporary implants - one of few examples are 192Ir hairpins for tongue implants


Problems with handling activity in the operating theatre

• Potential of lost sources

• The time to place the sources in the best possible locations is typically limited

• Radiation protection of staff may require awkward operation


Afterloading

• Implant only empty applicator or needles/catheters in theatre

• Once patient has recovered, dummy sources are introduced to verify the location of the applicators (typically using diagnostic X Rays)

• The treatment is planned

• The sources are introduced into the applicator or needle/catheter


Afterloading

• Manual• The sources are placed

manually usually by a physicist

• The sources are removed only at the end of treatment

• Remote• The sources are driven

from an intermediate safe into the implant using a machine (“afterloader”)

• The sources are withdrawn every time someone enters the room


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 radiation safety (in particular if a remote afterloader is used)

Quick question:

Why is afterloading the method of choice from a radiation safety perspective?


Some radiation safety aspects of afterloading

• No exposure in theatre

• Optimization of medical exposure possible

• No transport of a radioactive patient necessary

‘Live’ implants should be avoided for temporary implants


Applicators for brachytherapy


Brachytherapy Applicators - lots to choose from, lots to learn


Some examples for applicators

• Gynaecological applicators

Fletcher Suit

Henschke typeRing type


Rotterdam Applicator

TandemLengths(in mm)

40506070

Ovoid Sizes

SmallMediumLarge

• A choice of sizes allows customized treatment of each patient


Close-up view


Other intracavitary applicators

• Vaginal • Bronchus


Interstitial applicators

• Needles• hollow and rigid

• may use templates for placement

• usually have pusher during implantation in tissue


Interstitial applicators

• Catheters• flexible

• open and closed end available

• often introduced into tissue via an open end needle

skin


3. Delivery modes and equipment

• Low Dose Rate (LDR)

• Medium Dose Rate (MDR)

• High Dose Rate (HDR)

• Pulsed Dose Rate (PDR)


Delivery modes - different classifications 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


Low dose rate brachytherapy

• The only type of brachytherapy possible with manual afterloading

• Most clinical experience available for LDR brachytherapy

• Performed with remote afterloaders using 137-Cs or 192-Ir


Low dose rate brachytherapy

• Selectron for gynecological brachytherapy

• 137-Cs pellets pushed into the applicators using compressed air

• 6 channels for up to two parallel treatments

Nucletron


Simple design

• No computer required

• Two independent timers

• Optical indication of source locations

• Permanent record through printout

• Key to avoid unauthorized use


Treatment process

• Implant of applicator (typically in the operating theatre)

• Verification of applicator positioning using diagnostic X Rays (e.g. radiotherapy simulator)


Two orthogonal views allow to localize the applicator in three dimensions


Treatment planning

• Most commercial treatment planning systems have a module suitable for brachytherapy planning:• Choosing best source configuration

• Calculate dose distribution

• Determine time required to give desired dose at prescription points

• Record dose to critical structures


Treatment planning of different brachytherapy implants


High Dose Rate Brachytherapy

• Most modern brachytherapy is delivered using HDR

• Reasons?• Outpatient procedure

• Optimization possible


HDR brachytherapy

• In the past possible using 60-Co pellets

• Today, virtually all HDR brachytherapy is delivered using a 192-Ir stepping source

Source moves step by stepthrough the applicator - the

dwell times in different locationsdetermine the dose distribution


HDR 192-Ir source

From presentation by Pia et al.

Source length 5mm, diameter 0.6mmActivity: around 10Ci


Optimization of dose distribution adjusting the dwell times of the source in an applicator

Nucletron


HDR brachytherapy procedure

• Implant of applicators, catheters or needles in theatre

• For prostate implants as shown here use transrectal ultrasound guidance


HDR brachytherapy procedure

• Localization using diagnostic X Rays


Treatment planning

• Definition of the desired dose distribution (usually using many points)

• Computer optimization of the dwell positions and times for the treatment


Treatment

• Transfer of date to treatment unit

• Connecting patient

• Treat... Gammamed

Nucletron


HDR unit interface


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 >6hours to allow normal tissue to repair all damage


HDR units: different designs available


Catheters are indexed to avoid mixing them up

Transfer catheters are locked intoplace during treatment - green light

indicates the catheters in use


HDR systems

• Can be moved between different facilities or into theatre for intra-operative work


Pulsed dose rate

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

• Stepping source operation - same optimization possible as in HDR

• Treatment over same time as LDR treatment to mimic favorable radiobiology

• In-patient treatment: hospitalization required

• Source steps out for about 10 minutes per hour and then retracts. Repeats this every hour to deliver minifractions (‘pulses’) of about 1Gy


Pulsed dose rate brachytherapy

• Different dose/time pattern possible

• Usually treatment about once per hour

• Illustration form ICRU report 58


Features of PDR:

• Advantages Emulates LDR Optimized dose

distribution Visitors and nursing

staff can use the time between pulses while the activity is in the safe

• Disadvantages- Potential radiation safety

hazard of a source stuck in the patient:

In LDR - low activity, no severe problem

In HDR - physicist is present during treatment

In PDR - will someone with sufficient training be there within 10 minutes? Even at midnight???

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.


The answer should include:

• Advantages Out patient procedure Optimization of dose

distribution using stepping source

Possibly better geometry as patient anesthetized

No exposure of nursing staff during procedure

No source preparation

• DisadvantagesPotential radiobiological

disadvantageFractionation requiredMore shielding requiredThere is no time to

intervene if machine failure occurs

More sophisticated (and expensive)

Documents

Radiation Protection in Radiotherapy Part 6 Brachytherapy Lecture 2: Brachytherapy Techniques IAEA Training Material on Radiation Protection in Radiotherapy