Radiation Protection in Radiotherapy

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Radiation Protection inRadiotherapy
IAEA Training Material on Radiation Protection in
Radiotherapy

• Part 11
• Medical Exposure Brachytherapy
• Lecture 1 (cont.) Sources, implant techniques
  and equipment

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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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Design Considerations (BSS appendix II.11)

• 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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Defence in depth example Timers

• Need two completely independent timers
• One should count time up, one down
• Should be tested regularly

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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.

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Remote Afterloading Equipment

• The most complex pieces of equipment in
  brachytherapy
• Low dose rate units
• High dose rate units
• Many important design consideration in IEC
  standard

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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
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Other features

• No computer required
• Two independent timers
• Optical indication of source locations
• Permanent record through printout
• Key to avoid unauthorized use

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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
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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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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

• Important design issue - connectors and transfer
  tubes must be well designed and checked
• Should be labelled and easily identifiable

The correct channel of the afterloader must be
connected to the correct applicator/needle in the
patient
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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

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Regular maintenance is required

• Maintenance work should follow manufacturers
  recommendations
• All modifications MUST be documented
• A physicist should be notified to perform
  appropriate tests

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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

• 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

• 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

• 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)

Courtesy Siemens
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Auxiliary equipment for brachytherapy

• 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

• 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

• 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

• 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

• Maybe due to kink in catheter or other problems
• In the case of HDR, the source MUST be removed
  within lt 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

• Maybe due to kink in catheter or other problems
• In the case of HDR, the source MUST be removed
  within lt 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)

The procedure must be trained regularly
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Transfer of sources to the patient in
afterloading procedures

• 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

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

• One must ensure that ALL sources are removed from
  the patient
• This requires
• accounting of sources
• monitoring of the patient

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After a temporary implant is completed

• One must ensure that ALL sources are stored
  safely
• This requires
• accounting of sources
• monitoring of the patient
• monitoring of the room

• 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

• 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

• Iodine-125 Prostate Implant
• 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
• 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

• 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

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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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Any questions?
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Question

• Please provide a list of equipment which you
  would expect to find in a hot lab used for
  preparation of sources for brachytherapy

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Issues and items for the Hot Lab

• Good ventilation and lighting
• Close to brachytherapy treatment area
• Lockable
• Shielding as required
• Appropriate signs and documentation
• Equipped with
• 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