Transcript of Radiation Protection in Radiotherapy Part 6 Brachytherapy Lecture 2 (cont.): Brachytherapy...
- Slide 1
- Radiation Protection in Radiotherapy Part 6 Brachytherapy
Lecture 2 (cont.): Brachytherapy Techniques IAEA Training Material
on Radiation Protection in Radiotherapy
- Slide 2
- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques2 Brachytherapy l Very flexible
radiotherapy delivery l Allows a variety of different approaches,
creating the opportunity for special and highly customized
techniques l Not only used for malignant disease (=cancer)
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques3 Special techniques A. Prostate seed
implants B. Endovascular brachytherapy C. Ophthalmic applicators D.
Other special techniques Both point B and C are examples for the
use of brachytherapy for non-oncological purposes
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques4 A. 125-I seeds for prostate implants l
Relatively new technique l Indicated for localized early stage
prostate cancer l Permanent implant l Preferred by many patients as
it only requires one day in hospital
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques5 Treatment Options for prostate cancer l
Seed Implant Monotherapy (about 144Gy) l EBT (45Gy) + Implant Boost
n Seed Implant (108Gy) n HDR Implant (16.5Gy/3) l External Beam
only (65-84Gy) l Surgery (Radical Prostatectomy) This all could be
combined with hormones and/or chemotherapy
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques6 Implant schematic
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques7 A typical implant l Deliver 144 Gy to
entire prostate gland l Approximately 100 I-125 seeds (25 needles)
l Needles are guided by ultrasound and a template grid l
Pre-planned needle positions to give even dose but avoid pubic arch
l Minimise rectal dose and avoid urethra overdose l CT after 3
weeks for post-planning
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques8 l Palladium 103 - 108Gy - Pd -103 n Half
Life = 17 days - dose rate about 2.5 times larger than for 125-I n
Energy = 22 keV n TVL lead = 0.05mm Isotopes in use l Iodine 125 -
144Gy - I-125 n Half Life = 60 days n Energy = 28 keV n TVL lead =
0.08mm
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques9 Prostate Implant Process l Ultrasound
Volume Study l Pre-planning: what would be ideal l Ordering I-125
seeds and calibration l Needle loading l Ultrasound guided
Implantation l CT post-planning a couple of weeks after: what has
been achieved?
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques10 Patient flow in brachytherapy Treatment
decision Ideal plan - determines source number and location Implant
of sources or applicators in theatre Treatment plan Localization of
sources or applicators (typically using X Rays) Commence
treatment
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques11 Pre-planning l Several different systems
possible l Provides guidance for approach, data on number of
sources required and loading of needles l Avoid central column to
spare urethra l Cover target laterally l Conform to posterior
border (spare rectum)
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques12 Preparation of seeds l Ordering planned
number of seeds + some spares l Checking seed activity l Sorting
and loading seeds into needles Seed alignment tray
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques13 Implant needle loaded with seeds and
spacers
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques14 Implant template
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques15 Implant jig
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques16 Ultrasound Guided Implant Procedure
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques17 X-ray of implanted seed
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques18 CT post-planning after 4 weeks Swelling
is gone - CT provides true three dimensional information on the
implant geometry
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques19 Post CT planning = establishing the
actual dose distribution
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques20 Patient flow in brachytherapy Treatment
decision Ideal plan - determines source number and location Implant
of sources or applicators in theatre Treatment plan Localization of
sources or applicators (typically using X Rays) Commence
treatment
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques21 Quality of Implant l Depends on seed
placement l Seeds may migrate with time l If large dose
inhomogeneities exist, the critical cold spots can be boosted by
either placing more seeds in the prostate or using external beam
radiotherapy
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques22 Notes on prostate seed implants l A
similar technique is available using 103-Pd seeds n 103-Pd has a
shorter half life and therefore a higher activity is implanted n
Otherwise the rules an considerations are similar to 125-I seed
implants
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques23 2. Endovascular brachytherapy
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques24 The issue: re-stenosis l After opening
of a blocked blood vessel there is a high (60%+) likelihood that
the vessel is blocked again: Re-stenosis l Radiation is a proven
agent to prevent growth of cells l Radiation has been shown to be
effective in preventing re-stenosis
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques25 Dilation of blood vessels l Mostly for
cardiac vessels but also possible in some extremities
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques26 Endovascular irradiation l Mostly for
cardiac vessels but also possible in some extremities l Many
different systems and isotopes in use
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques27 Isotopes for endovascular brachytherapy
l Gamma sources: 192-Ir n the first source which has been
clinically used (Terstein et al. N Eng J Med 1996) l Beta sources:
32-P, 90-Sr/Y, 188-Rh (Rhenium) l Activity around 1Ci Dose
calculation
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques28 Beta sources l Most commercial systems
use them because: n finite range in tissues n less radiation safety
issues in the operating theatre n smaller, hand held units possible
for use in cardiac theatres l Potential problem: may not reach all
cells of interest
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques29 The Beta-Cath System (Novoste)
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques30 Guidant system l Employs centering
catheter to ensure source is always in the center of the
vessel
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques31 Radiation safety in theatre l
Application of radiation in theatre: n time is of the essence -
planning in situ n shielding would be difficult n physicists must
be present
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques32 Irradiation of extended lesions l Use
Radiation Source Train l Stepping source process to cover desired
length Longitudinal Dose Distribution 50 % 100 % 0 % L/2L/2
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques33 Angiographic Appearance of PDL in
Delivery Catheter
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques34 Radiation Source Train: Dose Profile at
2mm Radiation Source Train: Dose Profile at 2mm 40mm Radiation
Source Train (RST)
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques35 Radioactive stents l Stents are used to
keep blood vessels open l Can be impregnated with radioactive
material (typically 32-P) to help prevention of re- stenosis
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques36 C. Ophthalmic applicators l Treatment of
pterigiums and corneal vasculations, a non- oncological application
of radiotherapy l Use of beta sources - mostly 90-Sr/Y l Typical
activity 40 to 200MBq (10-50mCi)
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques37 Ophthalmic applicators l Activity
covered by thin plated gold or platinum l Curvature to fit the ball
of the eye l Diameter 12 to 18mm l Activity may only be applied to
parts of the applicator l Typical treatment time for several Gy
less than 1min
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques38 Decay scheme of 90 Sr / 90 Y 90 Sr 90 Y
90 Zr 0.54 MeV, T 1/2 = 28.5 yrs 2.25 MeV, T 1/2 = 64 hrs
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques39 Dept Dose Curve of 90 Sr in H 2 O Finite
treatment depth
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques40 Issues with ophthalmic applicators -
dosimetry l Dosimetry difficult due to short range of particles l
Dose uncertainty > 10% l Short treatment times taken from look-
up tables - potential for mistakes l Documentation often less than
complete
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques41 Other guidance and issues l Never point
source at someone - range in tissue 1m!!! l Radiation typically
used by non radiotherapy staff (eye specialists, nurses) - training
required l Sterilisation/cleaning - must not affect integrity of
the cover l Regular check of homogenous distribution of activity
required l Wipe tests required
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques42 D. Other specialized brachytherapy
applications l Intra-operative brachytherapy n Use of radiation in
operating theatre n Useful for incomplete surgical removal of
cancer n Allows highly topical application of radiation n If
surgery is followed by radiotherapy, one is 10Gy ahead in tumor
dose
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques43 Intra-operative brachytherapy l In
practice not often used because n not always possible to predict if
radiation will be needed during the operation n requires radiation
oncologist to be available n radiation safety issues sshielded
theatre costly spatient must be left alone during irradiation seven
if less than 5min this is a risk due to anesthetics
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques44 A note on radiation protection l Many
specialized brachytherapy applications are performed outside of a
conventional radiotherapy department - this requires consideration
of: n training n shielding n communication l Excellent planning and
documentation is required
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques45 Intra-operative brachytherapy l In
principle possible l Treatment units (must be HDR) available l
Applicators are available
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques46 Summary I l Brachytherapy is a highly
customized and flexible treatment modality l Quality of treatment
depends on operator skills l From a radiation protection point of
view remote afterloading is most desirable: A variety of equipment
is available to deliver remote afterloading brachytherapy l HDR
brachytherapy is the most common delivery mode nowadays.
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques47 Summary II l 125-I seed implants are a
alternative for radiotherapy of early prostate cancer l
Endovascular brachytherapy is one of an increasing number of
non-oncological applications of brachytherapy l There may be
radiation safety issues if specialized brachytherapy procedures are
performed outside of a radiotherapy department as staff not used to
working with ionizing radiation is using radioisotopes
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques48 References l l Nath et al. Intravascular
brachytherapy physics. AAPM TG60 report. Med. Phys. 26 (1999)
119-152 l l Waksman R and Serray P: Handbook of vascular
brachytherapy (London: Martin Dunitz) 1998
- Slide 49
- Any questions?
- Slide 50
- Question: Please list some radiation safety issues when using
90-Sr/Y applicators for ophthalmic treatments - you should consider
the appendices of BSS to classify them...
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques51 Radiation Safety Issues when using
90-Sr/Y applicators l Occupational exposure: n cleaning n
sterilization n contamination n handling of sources by
non-radiotherapy staff
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques52 Radiation Safety Issues when using
90-Sr/Y applicators l Medical exposure: n dosimetry difficult n
contamination from damaged applicator n over/under exposure of the
eye of the patient n irradiation of other areas of the patient
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques53 Radiation Safety Issues when using
90-Sr/Y applicators l Public exposure: n transport of the sources n
security of sources n storage and disposal
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- Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques54 Acknowledgement l Craig Lewis, London
Regional Cancer Centre l Mamoon Haque, RPA Hospital