Radiation Protection in Radiotherapy Part 6 Brachytherapy Lecture 2 (cont.): Brachytherapy Techniques IAEA Training Material on Radiation Protection in Radiotherapy

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)

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

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

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) è This all could be combined with hormones and/or chemotherapy

Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.): Brachytherapy techniques6 Implant schematic

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

Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.): Brachytherapy techniques8 l Palladium Gy - 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 Gy - I-125 n Half Life = 60 days n Energy = 28 keV n TVL lead = 0.08mm

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?

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

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)

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

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 techniques14 Implant template

Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.): Brachytherapy techniques15 Implant jig

Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.): Brachytherapy techniques16 Ultrasound Guided Implant Procedure

Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.): Brachytherapy techniques17 X-ray of implanted seed

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

Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.): Brachytherapy techniques19 Post CT planning = establishing the actual dose distribution

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

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

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 techniques23 2. Endovascular brachytherapy

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

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

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

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

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

Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.): Brachytherapy techniques29 The Beta-Cath™ System (Novoste)

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

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

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

Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.): Brachytherapy techniques33 Angiographic Appearance of PDL in Delivery Catheter

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)

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

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)

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

Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.): Brachytherapy techniques38 Decay scheme of 90 Sr / 90 Y 90 Sr 90 Y 90 Zr ß 0.54 MeV, T 1/2 = 28.5 yrs ß 2.25 MeV, T 1/2 = 64 hrs

Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.): Brachytherapy techniques39 Dept Dose Curve of 90 Sr in H 2 O Finite treatment depth

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

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

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

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

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

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

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.

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

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) l l Waksman R and Serray P: Handbook of vascular brachytherapy (London: Martin Dunitz) 1998

Any questions?

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...

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

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

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

Radiation Protection in RadiotherapyPart 6, lecture 2 (cont.): Brachytherapy techniques54 Acknowledgement l Craig Lewis, London Regional Cancer Centre l Mamoon Haque, RPA Hospital