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Radiation Protection in Radiotherapy

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

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Radiation Protection in Radiotherapy

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

  2. Brachytherapy • Very flexible radiotherapy delivery • Allows a variety of different approaches, creating the opportunity for special and highly customized techniques • Not only used for malignant disease (=cancer) Part 6, lecture 2 (cont.): Brachytherapy techniques

  3. 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 Part 6, lecture 2 (cont.): Brachytherapy techniques

  4. A. 125-I seeds for prostate implants • Relatively new technique • Indicated for localized early stage prostate cancer • Permanent implant • Preferred by many patients as it only requires one day in hospital Part 6, lecture 2 (cont.): Brachytherapy techniques

  5. Treatment Options for prostate cancer • Seed Implant Monotherapy (about 144Gy) • EBT (45Gy) + Implant Boost • Seed Implant (108Gy) • HDR Implant (16.5Gy/3) • External Beam only (65-84Gy) • Surgery (Radical Prostatectomy) • This all could be combined with hormones and/or chemotherapy Part 6, lecture 2 (cont.): Brachytherapy techniques

  6. Implant schematic Part 6, lecture 2 (cont.): Brachytherapy techniques

  7. A typical implant • Deliver 144 Gy to entire prostate gland • Approximately 100 I-125 seeds (25 needles) • Needles are guided by ultrasound and a template grid • Pre-planned needle positions to give even dose but avoid pubic arch • Minimise rectal dose and avoid urethra overdose • CT after 3 weeks for post-planning Part 6, lecture 2 (cont.): Brachytherapy techniques

  8. Iodine 125 - 144Gy - I-125 Half Life = 60 days Energy = 28 keV TVL lead = 0.08mm Isotopes in use • Palladium 103 - 108Gy - Pd -103 • Half Life = 17 days - dose rate about 2.5 times larger than for 125-I • Energy = 22 keV • TVL lead = 0.05mm Part 6, lecture 2 (cont.): Brachytherapy techniques

  9. Prostate Implant Process • Ultrasound Volume Study • Pre-planning: what would be ideal • Ordering I-125 seeds and calibration • Needle loading • Ultrasound guided Implantation • CT post-planning a couple of weeks after: what has been achieved? Part 6, lecture 2 (cont.): Brachytherapy techniques

  10. Pre-planning • Several different systems possible • Provides guidance for approach, data on number of sources required and loading of needles • Avoid central column to spare urethra • Cover target laterally • Conform to posterior border (spare rectum) Part 6, lecture 2 (cont.): Brachytherapy techniques

  11. Preparation of seeds • Ordering planned number of seeds + some spares • Checking seed activity • Sorting and loading seeds into needles Seed alignment tray Part 6, lecture 2 (cont.): Brachytherapy techniques

  12. Implant needle loaded with seeds and spacers Part 6, lecture 2 (cont.): Brachytherapy techniques

  13. Implant template Part 6, lecture 2 (cont.): Brachytherapy techniques

  14. Implant jig Part 6, lecture 2 (cont.): Brachytherapy techniques

  15. Ultrasound Guided Implant Procedure Part 6, lecture 2 (cont.): Brachytherapy techniques

  16. X-ray of implanted seed Part 6, lecture 2 (cont.): Brachytherapy techniques

  17. CT post-planning after 4 weeks Swelling is gone - CT provides true three dimensional information on the implant geometry Part 6, lecture 2 (cont.): Brachytherapy techniques

  18. Post CT planning = establishing the actual dose distribution Part 6, lecture 2 (cont.): Brachytherapy techniques

  19. Quality of Implant • Depends on seed placement • Seeds may migrate with time • 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 Part 6, lecture 2 (cont.): Brachytherapy techniques

  20. Notes on prostate seed implants • A similar technique is available using 103-Pd seeds • 103-Pd has a shorter half life and therefore a higher activity is implanted • Otherwise the rules an considerations are similar to 125-I seed implants Part 6, lecture 2 (cont.): Brachytherapy techniques

  21. 2. Endovascular brachytherapy Part 6, lecture 2 (cont.): Brachytherapy techniques

  22. The issue: re-stenosis • After opening of a blocked blood vessel there is a high (60%+) likelihood that the vessel is blocked again: Re-stenosis • Radiation is a proven agent to prevent growth of cells • Radiation has been shown to be effective in preventing re-stenosis Part 6, lecture 2 (cont.): Brachytherapy techniques

  23. Dilation of blood vessels • Mostly for cardiac vessels but also possible in some extremities Part 6, lecture 2 (cont.): Brachytherapy techniques

  24. Endovascular irradiation • Mostly for cardiac vessels but also possible in some extremities • Many different systems and isotopes in use Part 6, lecture 2 (cont.): Brachytherapy techniques

  25. Isotopes for endovascular brachytherapy • Gamma sources: 192-Ir • the first source which has been clinically used (Terstein et al. N Eng J Med 1996) • Beta sources: 32-P, 90-Sr/Y, 188-Rh (Rhenium) • Activity around 1Ci Dose calculation Part 6, lecture 2 (cont.): Brachytherapy techniques

  26. Beta sources • Most commercial systems use them because: • finite range in tissues • less radiation safety issues in the operating theatre • smaller, hand held units possible for use in cardiac theatres • Potential problem: may not reach all cells of interest Part 6, lecture 2 (cont.): Brachytherapy techniques

  27. The Beta-Cath™ System (Novoste) Part 6, lecture 2 (cont.): Brachytherapy techniques

  28. Guidant system • Employs centering catheter to ensure source is always in the center of the vessel Part 6, lecture 2 (cont.): Brachytherapy techniques

  29. Radiation safety in theatre • Application of radiation in theatre: • time is of the essence - planning in situ • shielding would be difficult • physicists must be present Part 6, lecture 2 (cont.): Brachytherapy techniques

  30. Irradiation of extended lesions • Use “Radiation Source Train” • Stepping source process to cover desired length 100 % Longitudinal Dose Distribution 50 % 0 % L/2 L/2 Part 6, lecture 2 (cont.): Brachytherapy techniques

  31. Angiographic Appearance of PDL in Delivery Catheter Part 6, lecture 2 (cont.): Brachytherapy techniques

  32. Radiation Source Train: Dose Profile at 2mm 40mm Radiation Source Train (RST) Part 6, lecture 2 (cont.): Brachytherapy techniques

  33. Radioactive stents • Stents are used to keep blood vessels open • Can be impregnated with radioactive material (typically 32-P) to help prevention of re-stenosis Part 6, lecture 2 (cont.): Brachytherapy techniques

  34. C. Ophthalmic applicators • Treatment of pterigiums and corneal vasculations, a non-oncological application of radiotherapy • Use of beta sources - mostly 90-Sr/Y • Typical activity 40 to 200MBq (10-50mCi) Part 6, lecture 2 (cont.): Brachytherapy techniques

  35. Ophthalmic applicators • Activity covered by thin plated gold or platinum • Curvature to fit the ball of the eye • Diameter 12 to 18mm • Activity may only be applied to parts of the applicator • Typical treatment time for several Gy less than 1min Part 6, lecture 2 (cont.): Brachytherapy techniques

  36. Decay scheme of 90Sr / 90Y 90Sr ß 0.54 MeV, T1/2 = 28.5 yrs 90Y ß 2.25 MeV, T1/2 = 64 hrs 90Zr Part 6, lecture 2 (cont.): Brachytherapy techniques

  37. Dept Dose Curve of 90Sr in H2O Finite treatment depth Part 6, lecture 2 (cont.): Brachytherapy techniques

  38. Issues with ophthalmic applicators - dosimetry • Dosimetry difficult due to short range of particles • Dose uncertainty > 10% • Short treatment times taken from look-up tables - potential for mistakes • Documentation often less than complete Part 6, lecture 2 (cont.): Brachytherapy techniques

  39. Other guidance and issues • Never point source at someone - range in tissue <1cm, but in air > 1m!!! • Radiation typically used by non radiotherapy staff (eye specialists, nurses) - training required • Sterilisation/cleaning - must not affect integrity of the cover • Regular check of homogenous distribution of activity required • Wipe tests required Part 6, lecture 2 (cont.): Brachytherapy techniques

  40. D. Other specialized brachytherapy applications • Intra-operative brachytherapy • Use of radiation in operating theatre • Useful for incomplete surgical removal of cancer • Allows highly topical application of radiation • If surgery is followed by radiotherapy, one is “10Gy ahead” in tumor dose Part 6, lecture 2 (cont.): Brachytherapy techniques

  41. Intra-operative brachytherapy • In practice not often used because • not always possible to predict if radiation will be needed during the operation • requires radiation oncologist to be available • radiation safety issues • shielded theatre costly • patient must be left alone during irradiation • even if less than 5min this is a risk due to anesthetics Part 6, lecture 2 (cont.): Brachytherapy techniques

  42. A note on radiation protection • Many specialized brachytherapy applications are performed outside of a conventional radiotherapy department - this requires consideration of: • training • shielding • communication • Excellent planning and documentation is required Part 6, lecture 2 (cont.): Brachytherapy techniques

  43. Intra-operative brachytherapy • In principle possible • Treatment units (must be HDR) available • Applicators are available Part 6, lecture 2 (cont.): Brachytherapy techniques

  44. Summary I • Brachytherapy is a highly customized and flexible treatment modality • Quality of treatment depends on operator skills • From a radiation protection point of view remote afterloading is most desirable: A variety of equipment is available to deliver remote afterloading brachytherapy • HDR brachytherapy is the most common delivery mode nowadays. Part 6, lecture 2 (cont.): Brachytherapy techniques

  45. Summary II • 125-I seed implants are a alternative for radiotherapy of early prostate cancer • Endovascular brachytherapy is one of an increasing number of non-oncological applications of brachytherapy • 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 Part 6, lecture 2 (cont.): Brachytherapy techniques

  46. References • Nath et al. Intravascular brachytherapy physics. AAPM TG60 report. Med. Phys. 26 (1999) 119-152 • Waksman R and Serray P: Handbook of vascular brachytherapy (London: Martin Dunitz) 1998 Part 6, lecture 2 (cont.): Brachytherapy techniques

  47. Any questions?

  48. 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...

  49. Radiation Safety Issues when using 90-Sr/Y applicators • Occupational exposure: • cleaning • sterilization • contamination • handling of sources by non-radiotherapy staff Part 6, lecture 2 (cont.): Brachytherapy techniques

  50. Radiation Safety Issues when using 90-Sr/Y applicators • Medical exposure: • dosimetry difficult • contamination from damaged applicator • over/under exposure of the eye of the patient • irradiation of other areas of the patient Part 6, lecture 2 (cont.): Brachytherapy techniques

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