Interstitial

Interstitial implant for breast

radiotherapy

Seven 192-Ir wires

Brachytherapy The use of radioactive sources in close

proximity to the target area for radiotherapy

Intracavitary

Intracavitary

gynecological implant

Three 137-Cs sources

Brachytherapy overview

Brachytherapy uses encapsulated

radioactive sources to deliver a high

dose to tissues near the source

brachys (Greek) = short (distance)

Inverse square law determines most of

the dose distribution

Brachytherapy

Characterized by strong

dose gradients

Many different techniques

and sources available

Implants are highly

customized for individual

patients

Brachytherapy

Use of radioactive materials in direct contact

with patients - more radiation safety issues

than in external beam radiotherapy

Less than 10% of radiotherapy patients are

treated with brachytherpay

Per patient treated the number of accidents in

brachytherapy is considerably higher than in

EBT

Contents

Brachytherapy Sources and equipment

Brachytherapy techniques

Objectives

To understand the concept of „sealed‟ source

To know the most common isotopes used for brachytherapy

To be familiar with general rules for source handling and testing

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

To understand the basic fundamentals of brachytherapy equipment design.

Brachytherapy Sources and Equipment

1. Sealed sources

IAEA BSS glossary: “Radioactive material that is a) permanently sealed in a capsule or b) closely bound and in a solid form.”

In other words: the activity is fixed to its carrier and contamination of the environment is not possible as long as the source is intact

Have an activity which can be derived from a calibration certificate and the half life of the isotope (nothing is lost)

MUST be checked for integrity regularly - a good means of doing this is by wipe tests

Sealed and unsealed sources in

radiotherapy

Both are used to treat cancer

Sealed sources are used for EBT and Brachytherapy - the Brachytherapy sources are discussed here

Unsealed sources may be used for systemic treatments – (Nuclear Medicine) as: 131-I for thyroid treatment

89-Sr and 153-Sm for treatment of bone metastasis.

2. The ideal source in Brachytherapy What do you think one would expect from and ideal

Brachytherapy source?

Clinical usefulness determined by

Half life = the time after which half of the

original activity is still present in the source

Specific activity = activity per gram of material.

The higher the smaller a source of a

particular activity can be made

Radiation energy determines the range of

radiation in tissue (AND the requirements for

shielding)

The Ideal Brachytherapy source

Pure gamma emitter - betas or alphas are too

short in range and result in very high doses to

small volumes around the source

Medium gamma energy

high enough to treat the target with homogenous

dose

low enough to avoid normal tissues and reduce

shielding requirements

High specific activity

suitable also for high dose rate applications

small

The Ideal Brachytherapy source

Stable daughter product

For temporaryمؤقت implants: long half life

allows economical re-use of sources

For permanent implants: medium half life

3. Real brachytherapy Sources

A variety of source types and isotopes are

currently in use

They differ for different applications because

of

half life,

size (specific activity) and

radiation energy

When deciding on a source one must also

keep the shielding requirements in mind.

Brachytherapy Sources Radionuclide 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 11.0

137Cs 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

125I 60.2 days 0.028 ave 0.025

103Pd 17.0 days 0.021 ave 0.008

Brachytherapy sources

The first isotope used clinically was radium

around 1903

However, radium and radon have only

historical importance - they should not be used

in a modern radiotherapy department

Brachytherapy sources

Because:

wide energy spectrum leading to high dose

close to the source and still high dose

around the patient - shielding difficult

Radon, the daughter product of radium, is a

noble gas which is very difficult to contain -

contamination risk

The long half life means disposal is very

difficult

Popular sources: 137-Cs

“Cesium 137”

Main substitute for radium

Mostly used in gynecological

applications

Long half life of 30 years ---> decay

correction necessary every 6 months

Sources are expensive and must be

replaced every 10 to 15 years

Popular sources: 192-Ir

“Iridium 192”

Many different forms available

Most important source for HDR applications

Medium half life (75 days) - decay correction

necessary for each treatment

Needs to be replaced every 3 to 4 months to

maintain effective activity and therefore an

acceptable treatment time

Popular sources: 192-Ir

“Iridium 192”

High specific activity - therefore even high

activity sources can be miniaturized essential

for HDR applications

A bit easier to shield than 137-Cs - because

the gamma energies of 192-Ir range from 136

to 1062keV (effective energy around 350keV)

Popular sources: 125-I

Very low energy - therefore shielding is

easy and radiation from an implant is

easily absorbed in the patient:

permanent implants are possible

Mostly used in the

form of seeds

125-I seeds

Many different designs

125-I seeds

Design aims and

features:

sealed source

non-toxic tissue

compatible encapsulation

isotropic dose distribution

radio-opaque for

localization

Mentor

X-ray visibility of 125-I seeds

Other isotopes used for seeds

Gold 198

Half Life = 2.7 days -

short enough to let

activity decay in the

patient

Energy = 412 keV

TVL lead = around

8mm

Palladium 103

Half Life = 17 days -

dose rate about 2.5

times larger than for

125-I

Energy = 22 keV

TVL lead = 0.05mm

Brachytherapy Sources 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

Source form examples

Seeds (discussed before): small containers for activity

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

implant such as prostate cancer

Needles and hairpins: for „life‟ implants in the operating theatre - activity

is directly introduced in the target region of the

patient

usually 192-Ir for temporary implants eg. of the

tongue

Scale in mm

Source form: 192-Ir wire

Used for LDR interstitial implants

Cut to appropriate length prior to implant to

suit individual patient

Cutting using manual technique or cutter...

Source form 192-Ir wires

192-Ir wire: activity between 0.5 and

10mCi per cm

used for interstitial

implants

low to medium dose rate

can be cut from 50 cm

long coils to the desired

length for a particular

patient Wire cutter

Movement

controls

Length

measurement Shielding

Source form example

192-Ir wire: activity between 0.5 and

10mCi per cm

used for interstitial

implants

low to medium dose rate

can be cut from 50 cm

long coils to the desired

length for a particular

patient Wire cutter

Movement

controls

Length

measurement Shielding

Question:

Why would people use 198-Au for brachytherapy?

Some clues for an answer

Key features of 198-Au are:

small sources (seed)

short half life (2.7 days)

inert material

photon energy 412keV

Therefore, ideal for permanent implant

Brachytherapy

Brachytherapy installations cover

direct source loading

137-Cs sources for gynaecological applications

(radium should not be used)

permanent seed implants (gold or 125-I)

surface applicators (moulds, 125-I, strontium

and ruthenium plaques

manual afterloading (137-Cs, 192-Ir)

automatic afterloading (LDR, PDR and

HDR)

Brachytherapy

Highly customized treatment techniques

- each patient is treated differently

Techniques depend on

Disease site and stage

Operator/clinician

Technology/equipment available

Many of the points covered for External Beam

installations also apply to Brachytherapy

installations, particularly for automatic

afterloading systems

Preparation of sources for

brachytherapy

Choosing the correct sources is an important

part of the implant optimization

This is applicable for situations when:

there are several different sources available (eg

137-Cs source with slightly different length and

activity for gynecological implants)

sources are ordered and customized for an

individual patient (eg. 192-Ir wire)

Require a pre-implant plan...

Choosing the correct sources

Prepare a plan for a

particular implant

following the prescription

Select appropriate

sources

If existing sources are to

be used select sources

from the safe and place in

transport container

Document what is done

safe

source

shielding

Interstitial implants

For LDR usually use

192-Ir wire

(compare part VI)

Optimization is

possible as the

length of the wire

can be adjusted for

a particular implant

HDR sources

No preparation necessary

Ensure

source calibration

optimized plan

Implant techniques

Permanent implants patient discharged with implant in place

Temporary implants implant removed before patient is discharged

Here particular emphasis on radiation

protection issues in medical exposures

Permanent Implants: Radiation

protection issues

Implant of activity in theatre:

Radiation protection of staff from a variety

of professional backgrounds - radiation

safety training is essential

RSO or physicist should be present

Source transport always necessary

Potential of lost sources

Problems with handling activity in

the operating theatre

The time to place the sources in the best possible locations is

typically limited

Work behind shields

or with other

protective equipment

may prolong

procedure and result

in sub-optimal access

to the patient

Working behind shields

Permanent Implants: 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 - compare part XV of the course

Temporary implants

Mostly done in afterloading technique

Radiation safety issues for staff:

Source handling and preparation

Exposure of nursing staff in manual

afterloading

Radiation safety issues for patients:

Source placement and removal

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)

Use of lead shield reduces scatter to the patient

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 step

through the applicator - the

dwell times in different locations

determine the dose distribution

HDR unit

interface

4. Brachytherapy equipment

Design considerations

often similar to external

beam therapy

Nucletron

Remote Afterloading Equipment

The most complex

pieces of equipment

in brachyhterapy

Low dose rate units

High dose rate units

Many important

design consideration

in IEC standard

Low dose rate brachytherapy

Selectron for gynecological

brachytherapy

137-Cs pellets pushed into the

applicators using compressed

air

Location of active and inactive

pellets can be chosen by the

operator to optimize the source

loading for an individual patient

Shown are 6 channels - the red

lights indicate the location of an

active source

Nucletron

Other features

No computer required

Two independent timers

Optical indication of

source locations

Permanent record

through printout

Key to avoid

unauthorized use

HDR brachytherapy units

Must be located in a

bunker

Have multiple

channels to allow

the same source to

drive into many

catheters/needles

MDS Nordion

Nucletron HDR unit control

Keypad

Display

Emergency off button

Key for source out

Memory card for transfer of the dwell positions

for the treatment of a particular patient - labeled

Key

Printout =

permanent record

Catheters are indexed to avoid

mixing them up

Transfer catheters are locked into

place during treatment - green light

indicates the catheters in use

Regular maintenance is required

Source drive must be

working within

specified accuracy

(typically 1-2mm)

Emergency buttons

must work

Manual retraction of

the source in case of

power failure must

work

Regular maintenance is required

Maintenance work

should follow

manufacturers

recommendations

All modifications

MUST be

documented

A physicists should

be notified to perform

appropriate tests

LDR and HDR units are not all...

Other brachytherapy equipment:

PDR (pulsed dose rate) units

Seed implant equipment

Endovascular brachytherapy

LDR and HDR units are not all...

Other brachytherapy equipment:

PDR units - similar to HDR

Seed implant equipment - discussed in

more detail in the second lecture of part VI

Endovascular brachytherapy

Typical Radiation Levels

Selectron LDR (Cs-137) Cervix insertion

10 pellets of 15 mCi/seed = 150 mCi

20 mR/h at 1m 0.2 mSv/h

5 days for 1 mSv (Background)

this is inside the room!

microSelectron HDR (Ir-192) turned ON!

10 Ci source = 10 000 mCi

4700 mR/h at 1m 47 mSv/h

1.3 minutes for 1 mSv (Background)

door interlock ensures that no-one is in room

Brachytherapy Techniques 1. Clinical brachytherapy applications

2. Implant techniques and applicators

3. Delivery modes and equipment

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

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 tumor

Often good performance status (must

tolerate the operation)

Sometimes pre-irradiated with external

beam radiotherapy (EBT)

Often treated with combination

brachytherapy and EBT

1. Clinical brachytherapy

applications

A. Surface moulds

B. Intracavitary (gynaecological, bronchus,..)

C. Interstitial (Breast, Tongue, Sarcomas, …)

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

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 brachytherapy 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

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

3. Delivery modes and

equipment

Low Dose Rate (LDR)

Medium Dose Rate

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 (eg

radiotherapy simulator)

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 step

through the applicator - the

dwell times in different locations

determine the dose distribution

HDR 192-Ir source

From presentation by Pia et al

Source length 5mm, diameter 0.6mm

Activity: 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

HDR prostate

implant:

Simulator image

Scout image for

CT scan

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 (eg. 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 into

place during treatment - green light

indicates the catheters in use

HDR systems

Can be moved eg

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

Feras Mansour Jargon

فراس منصور جرغون

IAEA Training Course: Radiation Protection in Radiotherapy slide 109