Transcript IAEA Training Material on Radiation Protection in Radiotherapy

IAEA Training Material on Radiation Protection in Radiotherapy
Radiation Protection in
Radiotherapy
Part 6
Brachytherapy
Lecture 2: Brachytherapy Techniques
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
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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)
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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
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Clinical brachytherapy
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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
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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 and
skill 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 (must
tolerate the operation)
• Sometimes pre-irradiated with external
beam radiotherapy (EBT)
• Often treated with combination
brachytherapy 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
Localization of sources or applicators
(typically using X Rays)
Treatment plan
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 training
material on radiation protection in Nuclear
Medicine
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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
during treatment
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Catheters for
source transfer
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Historical example
Surface applicator
with irregular
distribution of
radium on the
applicator surface
(Murdoch, Brussels
1933)
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Other example
Treatment of
squamous cell
carcinoma of
the forehead
Catheters for source
placement
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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
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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
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B. Intracavitary implants
• Introduction of radioactivity using an
applicator placed in a body cavity
• Gynaecological implants
• Bronchus
• Oesophagus
• Rectum
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Gynaecological implants
• Most common
brachytherapy application cervix cancer
• Many different applicators
• Either as monotherapy or
in 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 diameters
and length
Gammamed - on the right with shielding
Nucletron
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Bronchus implants
• Often palliative to open
air ways
• Usually HDR
brachytherapy
• Most often single
catheter, however also
dual catheter possible
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Dual catheter bronchus implant
• Catheter placement via
bronchoscope
• Bifurcation may create
complex dosimetry
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C. Interstitial implants
• Implant of needles or flexible catheters
directly in the target area
• Breast
• Head and Neck
• Sarcomas
• Requires surgery - often major
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Interstitial implants - tongue implant
Catheter loop
tongue
Button
tongue
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Breast implants
• Typically a boost
• Often utilizes templates to improve source
positioning
• 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 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)
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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)
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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
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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 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
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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
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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
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Afterloading
• Manual
• Remote
• The sources are placed
• The sources are driven
manually usually by a
physicist
• The sources are removed
only at the end of
treatment
from an intermediate
safe into the implant
using a machine
(“afterloader”)
• The sources are
withdrawn every time
someone enters the
room
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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 radiation
safety (in particular if a remote afterloader is
used)
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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
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Applicators for brachytherapy
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Brachytherapy Applicators - lots to
choose from, lots to learn
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Some examples for applicators
• Gynaecological applicators
Fletcher Suit
Henschke type
Ring type
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Rotterdam Applicator
• A choice of sizes allows customized
treatment of each patient
Tandem
Lengths
(in mm)
40
50
60
70
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Ovoid Sizes
Small
Medium
Large
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Close-up view
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Other intracavitary applicators
• Vaginal
• Bronchus
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Interstitial applicators
• Needles
• hollow and rigid
• may use templates
for placement
• usually have pusher
during implantation in
tissue
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Interstitial applicators
• Catheters
• flexible
• open and closed end
available
• often introduced into
tissue via an open
end needle
skin
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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)
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Delivery modes - different
classifications are in use
• Low Dose Rate
• Medium Dose Rate
• High Dose Rate
• Pulsed Dose Rate
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•
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•
•
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< 1Gy/hour
around 0.5Gy/hour
> 1Gy/hour
not often used
>10Gy/hour
pulses of around
1Gy/hour
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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
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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
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Simple design
• No computer required
• Two independent
timers
• Optical indication of
source locations
• Permanent record
through printout
• Key to avoid
unauthorized use
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Treatment process
• Implant of applicator (typically in the
operating theatre)
• Verification of applicator positioning
using diagnostic X Rays
(e.g. radiotherapy simulator)
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Two orthogonal views allow to localize the applicator in
three dimensions
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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
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Treatment planning of different
brachytherapy implants
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High Dose Rate Brachytherapy
• Most modern
brachytherapy is
delivered using HDR
• Reasons?
• Outpatient procedure
• Optimization possible
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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
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HDR 192-Ir source
Source length 5mm, diameter 0.6mm
Activity: around 10Ci
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From presentation by Pia et al.
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Optimization of dose distribution adjusting the
dwell times of the source in an applicator
Nucletron
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HDR brachytherapy procedure
• Implant of applicators, catheters or needles in theatre
• For prostate implants as shown here use transrectal
ultrasound guidance
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HDR brachytherapy procedure
• Localization using diagnostic X Rays
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Treatment planning
• Definition of the desired
dose distribution (usually
using many points)
• Computer optimization of
the dwell positions and
times for the treatment
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Treatment
• Transfer of date to treatment
unit
• Connecting patient
• Treat...
Gammamed
Nucletron
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HDR unit
interface
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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 >6hours
to allow normal tissue to repair all damage
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HDR units: different designs available
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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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HDR systems
• Can be moved
between different
facilities or into theatre
for intra-operative work
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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
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Pulsed dose rate brachytherapy
• Different dose/time
pattern possible
• Usually treatment
about once per hour
• Illustration form ICRU
report 58
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Features of PDR:
• Advantages
• Disadvantages
Emulates LDR
Optimized dose
distribution
Visitors and
nursing staff can
use the time
between pulses
while the activity is
in the safe
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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???
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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.
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
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• Disadvantages
Potential
radiobiological
disadvantage
Fractionation required
More shielding
required
There is no time to
intervene if machine
failure occurs
More sophisticated
(and expensive)
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