Brachytherapy

 The use of radioactive sources in close

proximity to the target area for radiotherapy
Interstitial

Seven 192-Ir wires

Interstitial implant for breast

radiotherapy
Intracavitary

Three 137-Cs sources

Intracavitary
gynecological implant
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
Brachytherapy Sources and
Equipment
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.
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 temporary‫ مؤقت‬implants: 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)
226
Ra 1600 years 0.047 - 2.45 (0.83 ave) 8.0
222
Rn 3.83 days 0.047 - 2.45 (0.83 ave) 8.0
60
Co 5.26 years 1.17, 1.33 11.0
137
Cs 30.0 years 0.662 5.5
192
Ir 74.2 days 0.136 - 1.06 (0.38 ave) 2.5
198
Au 2.7 days 0.412 2.5
125
I 60.2 days 0.028 ave 0.025
103
Pd 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
 Palladium 103  Gold 198
 Half Life = 17 days -  Half Life = 2.7 days -
dose rate about 2.5 short enough to let
times larger than for activity decay in the
125-I patient
 Energy = 22 keV  Energy = 412 keV
 TVL lead = 0.05mm  TVL lead = around
8mm
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): Scale in mm

 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
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: Length
Shielding
 activity between 0.5 and measurement
10mCi per cm
 used for interstitial
implants
 low to medium dose rate
 can be cut from 50 cm
long coils to the desired Movement
length for a particular controls
Wire cutter
patient
Source form example
 192-Ir wire: Length
Shielding
 activity between 0.5 and measurement
10mCi per cm
 used for interstitial
implants
 low to medium dose rate
 can be cut from 50 cm
long coils to the desired Movement
length for a particular controls
Wire cutter
patient
 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 safe

following the prescription source

 Select appropriate
sources
 If existing sources are to
be used select sources shielding
from the safe and place in
transport container
 Document what is done
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  Remote
 The sources are placed  The sources are driven
manually usually by a from an intermediate
physicist safe into the implant
 The sources are using a machine
removed only at the end (“afterloader”)
of treatment  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
Printout =
permanent record
Keypad
Emergency off button

Display

Key
Key for source out

Memory card for transfer of the dwell positions

for the treatment of a particular patient - labeled
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
Hand

A mould for the back

of a hand including
shielding designed to
protect the patient Catheters for
during treatment 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

Gammamed - on the right with shielding

Nucletron
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 Catheter loop

tongue

Button
tongue
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  < 1Gy/hour
around 0.5Gy/hour
 Medium Dose Rate  > 1Gy/hour
not often used
 High Dose Rate  >10Gy/hour
 Pulsed Dose Rate  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

Source length 5mm, diameter 0.6mm

Activity: around 10Ci

From presentation by Pia et al

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
Gammamed
 Treat...

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