Transcript IAEA Training Material on Radiation Protection in Radiotherapy

IAEA Training Material on Radiation Protection in Radiotherapy
Radiation Protection in
Radiotherapy
Part 11
Medical Exposure: Brachytherapy
Lecture 1 (cont.): Sources, implant techniques and
equipment
4. Brachytherapy equipment


Design considerations
often similar to external
beam therapy
Many points made in
part 10 of the course are
also relevant for
brachytherapy
Nucletron
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Part 11, lecture 1 (cont.): Equipment and rad. prot. issues
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Design Considerations
(BSS appendix II.11)
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“Equipment used in medical exposure
shall be so designed that:
failure of a single component of the system
be promptly detectable so that any
unplanned medical exposure of patients is
minimized
 the incidence of human error in the delivery
of unplanned medical exposure be
minimized”

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Part 11, lecture 1 (cont.): Equipment and rad. prot. issues
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Defence in depth example:
Timers
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Need two
completely
independent timers
One should count
time up, one down
Should be tested
regularly
Why not verify the elapsed time using your watch?
Radiation Protection in Radiotherapy
Part 11, lecture 1 (cont.): Equipment and rad. prot. issues
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Defence in depth example

Retraction of sources:
Normal power
 Backup battery (must be checked)
 Manual system
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Design Considerations BSS II.13

“Registrants and
licensees, in specific
co-operation with
suppliers
(a) the equipment conform to
applicable standards of the
International
Electrotechnical
Commission (IEC) and the
ISO or to equivalent
national standards
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BSS appendix II Design criteria
specific to radiotherapy

II.15. “Registrants and licensees, in specific
co-operation with suppliers, shall ensure that:
...
(e)
radioactive sources for either teletherapy or
brachytherapy be so constructed that they conform to
the definition of a sealed source; and
(f)
when appropriate, monitoring equipment be
installed or be available to give warning of an unusual
situation in the use of radiation generators and
radionuclide therapy equipment.”
Radiation Protection in Radiotherapy
Part 11, lecture 1 (cont.): Equipment and rad. prot. issues
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Remote Afterloading Equipment

The most complex
pieces of equipment
in brachytherapy
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Low dose rate units
High dose rate units
Many important
design consideration
in IEC standard
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Part 11, lecture 1 (cont.): Equipment and rad. prot. issues
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Low dose rate brachytherapy
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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
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Part 11, lecture 1 (cont.): Equipment and rad. prot. issues
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Other features
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No computer required
Two independent timers
Optical indication of
source locations
Permanent record
through printout
Key to avoid
unauthorized use
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Part 11, lecture 1 (cont.): Equipment and rad. prot. issues
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HDR brachytherapy units

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Must be located in a
bunker
Have multiple
channels to allow
the same source to
drive into many
catheters/needles
MDS Nordion
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Part 11, lecture 1 (cont.): Equipment and rad. prot. issues
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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 - labelled
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Part 11, lecture 1 (cont.): Equipment and rad. prot. issues
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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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Transfer of sources
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Important design
issue - connectors
and transfer tubes
must be well
designed and
checked
Should be labelled
and easily
The correct channel of the afterloader
identifiable
must be connected to the correct
applicator/needle in the patient
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Regular maintenance is required
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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
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Regular maintenance is required
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Maintenance work
should follow
manufacturers
recommendations
All modifications
MUST be
documented
A physicist should be
notified to perform
appropriate tests
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Part 11, lecture 1 (cont.): Equipment and rad. prot. issues
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LDR and HDR units are not all...

Other brachytherapy equipment:
PDR (pulsed dose rate) units
 Seed implant equipment
 Endovascular brachytherapy
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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 6
 Endovascular brachytherapy

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Endovascular brachytherapy
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Details of function
was discussed in
part 6
Some similarities to
HDR units, however,
different catheters
and sources are in
use
Courtesy Guidant
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Centering of the source in the
catheter
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May be important due
to short range of many
radiation sources
Improves dose
distribution on all vessel
walls
Courtesy Guidant
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For all equipment...
Operator must be familiar with the unit
 Maintenance staff must be trained and
aware of radiation protection issues
 Present course can not replace
manufacturer training
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Auxiliary equipment for
brachytherapy
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Diagnostic equipment
for localization of the
applicators and/or
sources
May be simulator
(compare part 10) or
other diagnostic units
(more details in the
course on diagnostics)
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Part 11, lecture 1 (cont.): Equipment and rad. prot. issues
Courtesy Siemens
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Auxiliary equipment for
brachytherapy
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Radiation Protection in Radiotherapy
Other equipment may also be
required with modifications for
brachytherapy.
Prior to each implant its
integrity must be checked as
patient safety and appropriate
treatment delivery can rely on
it.
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A note on intercom systems
Need to be able to see the patient - is
he/she comfortable? Is she/he moving?
 Need to be able to talk to the patient
 Need to be able to hear if the patient is
in distress
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5. Radiation protection issues in
brachytherapy
Patients, a variety of staff and
potentially visitors are involved
 Use of sources with high activity

Preparation of sources
 Insertion of sources
 Removal of sources
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Training and information: staff
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Training of staff is
essential
This applies to
radiation workers
and others, such as
domestic or
maintenance staff
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Information for patients
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Patients must be aware
of the particulars of
their treatment prior to it
commencing (and
consent to it)
It is often a shock for
patients waking up after
an operation with
catheters and needles
in place
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Source change in High Dose
Rate (HDR) Brachytherapy
Source change is required about every
3 to 4 months due to 192-Ir decay
 Is also required if any variations of
source movement from the planned
treatment are noticed or if a source
stuck in the patient...
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HDR brachytherapy source
change
Must be done by suitably qualified
personal
 Calibration of the new source is
essential - it is NOT appropriate to trust
the source certificate only
 Different calibration methods are
possible - more in the next lecture
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HDR brachytherapy source
change
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Need to ensure source
dimensions are
unchanged (fits in all
applicators)
Need to verify source
movement e.g. using a
suitable jig or a video
camera for observation
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A source stuck in the patient
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Maybe due to kink in catheter or other
problems
In the case of HDR, the source MUST be
removed within < 1min
This requires a suitably trained person (RSO,
medical physicist) to be present
Emergency procedures must be established
Relevant equipment must be present (e.g.
radiation monitor, crank to rewind the source
drive cable manually)
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A source stuck in the patient
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Maybe due to kink in catheter or other
problems
In the case of HDR, the source MUST be
removed within < 1min
ThisThe
requires
a suitably
trained
person (RSO,
procedure
must
be trained
medical physicist)
to be present
regularly
Emergency procedures must be established
Relevant equipment must be present (e.g.
radiation monitor, crank to rewind the source
drive cable manually)
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Transfer of sources to the patient in
afterloading procedures
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All source channels
in the patient must
be easily identifiable
Mix-up of channels
is a serious accident
Transfer pathways
should be kept as
short as possible
Radiation Protection in Radiotherapy
For HDR units the
transfer time may need to
be considered for the
treatment plan
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After a temporary implant is
completed
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One must ensure
that ALL sources are
removed from the
patient
This requires:
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accounting of
sources
monitoring of the
patient
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After a temporary implant is
completed
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One must ensure
that ALL sources are
stored safely
This requires:
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accounting of
sources
monitoring of the
patient
monitoring of the
room
Radiation Protection in Radiotherapy
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Room monitoring may
include the bed.
However, as only
sealed sources are
used in brachytherapy,
contamination of linen
and cloths is typically
not a problem
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Summary

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Due to the use of radioactive sources in direct
contact with the patient, brachytherapy has
the potential of radiation protection problems
Written procedures, protocols and adherence
to good design can eliminate many sources
of safety issues
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Typical Radiation Levels
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Iodine-125 Prostate Implant
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100 seeds of 0.36 mCi/seed = 36 mCi
less than 0.25 mR/h at 1m  0.0025 mSv/h
17 days for 1 mSv (Background)
Gold-198 seed lip implant
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8 seeds of 3 mCi/seed = 24 mCi
6 mR/h at 1m  0.06 mSv/h
17 hours for 1 mSv (Background)
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Typical Radiation Levels
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Selectron LDR (Cs-137) Cervix insertion
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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!
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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
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Part 11, lecture 1 (cont.): Equipment and rad. prot. issues
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Brachytherapy

Additional points covering safety
associated with brachytherapy
equipment are made in the lectures on
shielding (part 7) and on brachytherapy
(part 6).
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Part 11, lecture 1 (cont.): Equipment and rad. prot. issues
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Any questions?
Question:
Please provide a list of equipment which you would
expect to find in a hot lab used for preparation of
sources for brachytherapy
Issues and items for the Hot Lab
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Good ventilation and lighting
Close to brachytherapy treatment area
Lockable
Shielding as required
Appropriate signs and documentation
Equipped with:
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Telephone
Radiation Monitor
Well counter for calibration (or equivalent)
Shielded workbench
Safe for storage of sources
Safe for waste
Mobile storage safe
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Acknowledgement
Mamoon Haque, Royal Prince Alfred
Hospital, Sydney
 Craig Lewis, LRCC, London, Ontario

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