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)
Slide 3
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
Slide 4
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
Slide 5
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
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
Slide 8
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
Slide 9
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?
Slide 10
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
Slide 11
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)
Slide 12
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
Slide 13
Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques13 Implant needle loaded with seeds and
spacers
Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques17 X-ray of implanted seed
Slide 18
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
Slide 19
Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques19 Post CT planning = establishing the
actual dose distribution
Slide 20
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
Slide 21
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
Slide 22
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
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
Slide 25
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
Slide 26
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
Slide 27
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
Slide 28
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
Slide 29
Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques29 The Beta-Cath System (Novoste)
Slide 30
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
Slide 31
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
Slide 32
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
Slide 33
Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques33 Angiographic Appearance of PDL in
Delivery Catheter
Slide 34
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)
Slide 35
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
Slide 36
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)
Slide 37
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
Slide 38
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
Slide 39
Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques39 Dept Dose Curve of 90 Sr in H 2 O Finite
treatment depth
Slide 40
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
Slide 41
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
Slide 42
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
Slide 43
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
Slide 44
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
Slide 45
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
Slide 46
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.
Slide 47
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
Slide 48
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...
Slide 51
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
Slide 52
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
Slide 53
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
Slide 54
Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.):
Brachytherapy techniques54 Acknowledgement l Craig Lewis, London
Regional Cancer Centre l Mamoon Haque, RPA Hospital