Radiation Protection in Radiotherapy

1
Radiation Protection inRadiotherapy
IAEA Training Material on Radiation Protection in
Radiotherapy

• Part 11
• Medical Exposure Good Practice and Radiation
  Protection in Brachytherapy

2
Medical Exposure

• In brachytherapy the quality of the treatment
  depends mostly on the skills of the operator who
  places the applicators and/or sources in the
  patient - modern equipment allows the
  physicist/operator a certain degree of
  optimization after the actual implant has taken
  place.
• Brachytherapy uses radioactive sources which
  cannot be turned off like X Ray equipment
  typically used for external beam radiotherapy -
  therefore radiation protection is more likely to
  be an issue in brachytherapy than in EBT

3
Objectives

• To be familiar with the brachytherapy process
• To be able to discuss methods for brachytherapy
  planning and dosimetry
• To understand the optimization of dose delivery
  to the target by choosing appropriate isotopes
  and delivery techniques
• To understand the implications of the above for
  radiation safety

4
Contents

• Lecture 1 Sources, implant techniques and
  equipment - radiation protection aspects
• Lecture 2 Dosimetry, planning and verification

Lectures complement part 6 of the course and are
complemented by parts 14 to 16
5
Radiation Protection inRadiotherapy
IAEA Training Material on Radiation Protection in
Radiotherapy

• Part 11
• Medical Exposure Brachytherapy
• Lecture 1 Sources, implant techniques and
  equipment

6
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)

7
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

8
Objectives of lecture 1 in part 11

• To be aware of radiation safety issues when
  handling radioactive sources used for
  brachytherapy
• To be familiar with the brachytherapy process
• To understand the function of remote afterloading
  brachytherapy equipment
• To appreciate the scope for optimization in
  stepped source brachytherapy
• To understand the implications of the above for
  radiation safety

9
Contents

• 1. Source storage and handling
• 2. Preparation of sources for an implant
• 3. Implant techniques
• 4. Brachytherapy equipment
• 5. Radiation protection issues

10
1. Source storage and handling

• Radioactive sources must be under the control of
  an appropriate person at all times
• Ordering
• Receiving
• Storage
• Handling
• Use
• Disposal

11
Tests for Brachytherapy Sources

• The following should be done on receipt of the
  sources and documented
• Physical/chemical form
• Source encapsulation, wipe test
• Radionuclide distribution and uniformity
• Autoradiograph
• Uniformity of activity amongst seeds
• Visual inspection of seeds in ribbons

12
Source Storage

• Source stores must
• provide protection against environmental
  conditions
• be only for radioactive materials
• provide sufficient shielding
• be resistant to fire
• be secure
• be labelled

13
Features of source storage

• Secure (lock and key)
• Labels
• Different compartments
• Shielding
• Easy access
• Well organized

14
Transferring sources from and into a safe

• Use of tweezers
• Behind shielding
• Short transport ways

15
Safe for 137-Cs sources
Numbered and easily identifiable source draws
- color coding of sources
16
Commercially available isotope safe
Shielding of drawers
lockable
17
Storage and transport of 125-I seeds
Courtesy of Mentor
18
Storage room

• Must be lockable
• Check environmental conditions good lighting and
  ventilation
• Typically some source handling area should be
  available
• Radiation monitor must be available
• Regular (e.g. 6-monthly) checks of background
  exposure rate is recommended

19
Accountability of Sources

• Source accountancy records should contain
• radionuclide and activity of sources
• location and description of sources
• disposal details

• The records should be updated regularly, and the
  location of the sources checked.

20
Handling of sources

• General
• avoid contamination
• use gloves
• no eating/drinking in room
• use long forceps
• Let someone know if you work with radioactivity

21
Transport
Courtesy Nucletron

• More details in part 4
• Use a mobile safe - this can double up as
  emergency container

22
Disposal of sources

• More details in part 15
• Check activity prior to disposal
• Must be to a licensed operator
• Provide and keep appropriate records

23
Check of sources

• Frequency of tests depends on source type and
  isotope
• Tests should include a measure of dose and a
  check of source integrity
• Useful is a combination of auto-radiograph and X
  Ray of the source to assess integrity of the
  encapsulation and distribution of activity

24
2. 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
  (e.g. 137-Cs source with slightly different
  length and activity for gynecological implants)
• sources are ordered and customized for an
  individual patient (e.g. 192-Ir wire)

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Require a pre-implant plan...
26
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
27
Preparation of seeds

• Ordering planned number of seeds some (around
  10) spares
• Checking seed activity
• either all (one by one)
• or a representative subset (gt10)

Wellchamber courtesy of MedTec
28
Preparation of seeds

• Sorting seeds and inactive spacers into the
  desired pattern
• Loading seeds into needles

Seed alignment tray
29
Seed handling tools (MedTec)
Brass funnel to channel seeds into needles
or containers
Radiation monitor can locate lost seeds
30
Implant needle loaded with seeds and spacers
31
Interstitial implants

• For LDR usually use 192-Ir wire (compare part 6)
• Optimization is possible as the length of the
  wire can be adjusted for a particular implant

32
192-Ir wire for LDR implants

• Purchase 50cm coils of Iridium wire
• Sources are cut to length to suit a particular
  application

Extra shielding
Wire cutter
33
Source form 192-Ir wires

• Cut wire
• Encapsulate in a thin plastic sheath
• Seal ends (heat shrink)
• Can all be done in a purpose built cutter or
  manually

Length measurement
Shielding
Movement controls
Nucletron wire cutter
34
HDR sources

• No preparation necessary
• Ensure
• source calibration
• optimized plan

35
HDR source calibration

• Use of thimble type ionization chamber and
  calibration jig
• Or use of a well chamber
• In any case the calibration must be traceable to
  a standard laboratory

36
Rules for working with sealed Radioisotopes

• Never handle a source with your hands - use
  forceps. Long forceps are preferable to reduce
  dose rate
• Stand behind a shield when possible

37
Rules for working with sealed Radioisotopes

• Work efficiently - it may pay to rehearse a
  certain activity (e.g. putting active wire in a
  thin sheath) with inactive materials first
• Always wear a personnel monitor
• Always have an area monitor ON

38
Rules for working with sealed Radioisotopes

• Always survey the area after the sources are put
  away
• Survey gloves and equipment used
• Always log the activity

Radiation monitor
39
3. Implant techniques

• Compare part 6 of the course
• 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

40
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

41
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

42
Working behind shields
43
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 15 of the course

44
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

45
Nursing issues

• LDR brachytherapy patients are treated for up to
  one week in a ward requiring regular nursing
• If sources cannot be removed, there will be
  exposure to nursing staff
• Staff needs to be trained, informed and monitored
• Shielding should be employed

46
Shielded bed
47
Nursing issues

• Each implant is different - a physicist should
  monitor the patient once in bed and advise staff
  on the best approach for nursing
• Workload (and dose) could be shared amongst staff

48
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

49
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)

50
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
51
Design Considerations BSS appendix II.13

• Registrants and licensees, in specific
  co-operation with suppliers
• ...
• (g) exposure rates outside the examination or
  treatment area due to radiation leakage or
  scattering be kept as low as reasonably
  achievable

This typically implies the use of shielding which
is not straight forward in the case of
brachytherapy where sources are in direct contact
with a patient.
52
Shielding example for a radioactive mould
Treatment of superficial basal cell carcinoma of
the upper chest and lower neck
53
Use of lead shield reduces scatter to the patient
54
Shielding included in applicators
MDS Nordion

• e.g. vaginal applicators with rectal shielding
• Good means to optimize the medical exposure -
  however dosimetry is difficult

55
Shielded gynaecological applicators

• Shielding in the ovoid capsules
• Reduces dose to the rectum
• Dosimetry for treatment area not affected
  considerably

MDS Nordion
56
Some comments on the use of flexible catheters

• Catheters should be handled with absolute care to
  avoid any kinking or damage.
• The curvatures of catheter should be controlled
  to guarantee smooth movement of the source within
  it.
• While simulating, marker wires should be inserted
  completely into the catheters and taped securely
  to avoid any displacement.

57
High Dose Rate Brachytherapy

• Most modern brachytherapy is delivered using HDR
• Reasons?
• Outpatient procedure
• Optimization possible

58
High Dose Rate (HDR) Brachytherapy

• Small high activity source (about 10Ci) - these
  days nearly exclusively 192-Ir
• Source moves through implanted catheters and/or
  needles step by step
• The dwell times determine the dose distribution

59
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
60
Optimization of dose distribution adjusting the
dwell times of the source in an applicator
Nucletron
61
HDR unit interface
62
Issues with the optimization

• Can get rather complex when multiple catheters or
  needles are used
• Is a three dimensional process
• Requires in practice computerized treatment
  planning
• Must ensure the plan is properly transferred to
  the unit

63
Verification of proper source movement

• Unit monitors the source movement via the drive
  cable movement
• An independent radiation monitor outside of the
  patient can verify
• if the source is out of the safe
• if the source has returned to the safe after the
  desired treatment time has elapsed
• The operator should monitor this

64
Verification of source movement

• Measurement jig
• Film cassette for autoradiograph

MDS Nordion
Nucletron