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Radiation Protection in Radiotherapy

Radiation Protection in Radiotherapy

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Radiation Protection in Radiotherapy

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

  2. Brachytherapy • Very flexible radiotherapy delivery • Source position determines treatment success • Depends on operator skill and experience • In principle the ultimate ‘conformal’ radiotherapy • Highly individualized for each patient • Typically an inpatient procedure as opposed to external beam radiotherapy which is usually administered in an outpatient setting Part 6, lecture 2: Brachytherapy techniques

  3. Objectives • To be familiar with different implant techniques • To be aware of differences between permanent implants, low (LDR) and high dose rate (HDR) applications • To appreciate the potential for optimization in high dose rate brachytherapy • To be familiar with some special techniques used in modern brachytherapy (seed implants, endovascular brachytherapy) Part 6, lecture 2: Brachytherapy techniques

  4. Contents 1. Clinical brachytherapy applications 2. Implant techniques and applicators 3. Delivery modes and equipment 4. Special techniques • A. Prostate seed implants • B. Endovascular brachytherapy • C. Ophthalmic applicators Part 6, lecture 2: Brachytherapy techniques

  5. Clinical brachytherapy Part 6, lecture 2: Brachytherapy techniques

  6. History • Brachytherapy has been one of the earliest forms of radiotherapy • After discovery of radium by M Curie, radium was used for brachytherapy already late 19th century • There is a wide range of applications - this versatility has been one of the most important features of brachytherapy Part 6, lecture 2: Brachytherapy techniques

  7. Today • Many different techniques and a large variety of equipment • Less than 10% of radiotherapy patients receive brachytherapy • Use depends very much on training and skill of clinicians and access to operating theatre Part 6, lecture 2: Brachytherapy techniques

  8. A brachytherapy patient • Typically localized cancer • Often relatively small tumour • Often good performance status (must tolerate the operation) • Sometimes pre-irradiated with external beam radiotherapy (EBT) • Often treated with combination brachytherapy and EBT Part 6, lecture 2: Brachytherapy techniques

  9. Patient flow in brachytherapy Treatment decision Ideal plan - determines source number and location Implant of sources or applicators in theatre Localization of sources or applicators (typically using X Rays) Treatment plan Commence treatment Part 6, lecture 2: Brachytherapy techniques

  10. 1. Clinical brachytherapy applications A. Surface moulds B. Intracavitary (gynaecological, bronchus,..) C. Interstitial (Breast, Tongue, Sarcomas, …) not covered here: unsealed source radiotherapy (Thyroid, Bone metastasis, …) - this is dealt with in the IAEA training material on radiation protection in Nuclear Medicine Part 6, lecture 2: Brachytherapy techniques

  11. A. Surface moulds • Treatment of superficial lesions with radioactive sources in close contact with the skin Hand A mould for the back of a hand including shielding designed to protect the patient during treatment Catheters for source transfer Part 6, lecture 2: Brachytherapy techniques

  12. Historical example Surface applicator with irregular distribution of radium on the applicator surface (Murdoch, Brussels 1933) Part 6, lecture 2: Brachytherapy techniques

  13. Other example Treatment of squamous cell carcinoma of the forehead Catheters for source placement Part 6, lecture 2: Brachytherapy techniques

  14. Source distance from the skin • Determines incident dose • Determines dose fall off in skin - the further the sources are from the skin the less influence has dose fall off due to inverse square law • Dose homogeneity - the further away the sources are the more homogenous the dose distribution is at the skin Part 6, lecture 2: Brachytherapy techniques

  15. Simulator films of forehead mould Dummy wires as markers for location

  16. Surface mould advantages • Fast dose fall off in tissues • Can conform the activity to any surface • Flaps available Part 6, lecture 2: Brachytherapy techniques

  17. B. Intracavitary implants • Introduction of radioactivity using an applicator placed in a body cavity • Gynaecological implants • Bronchus • Oesophagus • Rectum Part 6, lecture 2: Brachytherapy techniques

  18. Gynaecological implants • Most common brachytherapy application - cervix cancer • Many different applicators • Either as monotherapy or in addition to external beam therapy as a boost Part 6, lecture 2: Brachytherapy techniques

  19. Gynecological applicators Different design - all Nucletron Part 6, lecture 2: Brachytherapy techniques

  20. Vaginal applicators • Single source line • Different diameters and length Gammamed - on the right with shielding Nucletron Part 6, lecture 2: Brachytherapy techniques

  21. Often palliative to open air ways Usually HDR brachytherapy Most often single catheter, however also dual catheter possible Bronchus implants Part 6, lecture 2: Brachytherapy techniques

  22. Dual catheter bronchus implant • Catheter placement via bronchoscope • Bifurcation may create complex dosimetry Part 6, lecture 2: Brachytherapy techniques

  23. C. Interstitial implants • Implant of needles or flexible catheters directly in the target area • Breast • Head and Neck • Sarcomas • Requires surgery - often major Part 6, lecture 2: Brachytherapy techniques

  24. Interstitial implants - tongue implant Catheter loop tongue Button tongue Part 6, lecture 2: Brachytherapy techniques

  25. Breast implants • Typically a boost • Often utilizes templates to improve source positioning • Catheters or needles Part 6, lecture 2: Brachytherapy techniques

  26. 2. Implant techniques and applicators • Permanent implants • patient discharged with implant in place • Temporary implants • implant removed before patient is discharged from hospital Part 6, lecture 2: Brachytherapy techniques

  27. Permanent implants • Implantation of sealed sources (typically seeds) into the target organ of the patient • Sources are NOT removed and patient is discharged with activity in situ (compare part 16 of the course) Part 6, lecture 2: Brachytherapy techniques

  28. 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 Discussed in more detail in parts 9 (Medical Exposure), 16 (Discharge of patients) and 17 (Public exposure) Part 6, lecture 2: Brachytherapy techniques

  29. Source requirement for permanent implants • Low energy gammas or betas to minimize radiation levels outside of the patient (125-I is a good isotope) • May be short-lived to reduce dose with time (198-Au is a good isotope) • More details on most common 125-I prostate implants in section 4A of the lecture Part 6, lecture 2: Brachytherapy techniques

  30. Temporary implants • Implant of activity in theatre • Manual afterloading • Remote afterloading Part 6, lecture 2: Brachytherapy techniques

  31. Implant of activity in theatre • (Common for permanent implants) • For temporary implants common practice 40 years ago when radium was commonly used • for example gynecological implants of radium or 137-Cs needles • Today only very rarely used for temporary implants - one of few examples are 192Ir hairpins for tongue implants Part 6, lecture 2: Brachytherapy techniques

  32. Potential of lost sources The time to place the sources in the best possible locations is typically limited Radiation protection of staff may require awkward operation Problems with handling activity in the operating theatre Part 6, lecture 2: Brachytherapy techniques

  33. Afterloading • Implant only empty applicator or needles/catheters in theatre • Once patient has recovered, dummy sources are introduced to verify the location of the applicators (typically using diagnostic X Rays) • The treatment is planned • The sources are introduced into the applicator or needle/catheter Part 6, lecture 2: Brachytherapy techniques

  34. 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 Afterloading Part 6, lecture 2: Brachytherapy techniques

  35. 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) Part 6, lecture 2: Brachytherapy techniques

  36. Quick question: Why is afterloading the method of choice from a radiation safety perspective?

  37. 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 Part 6, lecture 2: Brachytherapy techniques

  38. Applicators for brachytherapy Part 6, lecture 2: Brachytherapy techniques

  39. Brachytherapy Applicators - lots to choose from, lots to learn Part 6, lecture 2: Brachytherapy techniques

  40. Some examples for applicators • Gynaecological applicators Fletcher Suit Henschke type Ring type Part 6, lecture 2: Brachytherapy techniques

  41. Rotterdam Applicator • A choice of sizes allows customized treatment of each patient Part 6, lecture 2: Brachytherapy techniques

  42. Close-up view Part 6, lecture 2: Brachytherapy techniques

  43. Vaginal Bronchus Other intracavitary applicators Part 6, lecture 2: Brachytherapy techniques

  44. Interstitial applicators • Needles • hollow and rigid • may use templates for placement • usually have pusher during implantation in tissue Part 6, lecture 2: Brachytherapy techniques

  45. Interstitial applicators • Catheters • flexible • open and closed end available • often introduced into tissue via an open end needle skin Part 6, lecture 2: Brachytherapy techniques

  46. 3. Delivery modes and equipment • Low Dose Rate (LDR) • Medium Dose Rate (MDR) • High Dose Rate (HDR) • Pulsed Dose Rate (PDR) Part 6, lecture 2: Brachytherapy techniques

  47. Low Dose Rate Medium Dose Rate High Dose Rate Pulsed Dose Rate < 1Gy/hour around 0.5Gy/hour > 1Gy/hour not often used >10Gy/hour pulses of around 1Gy/hour Delivery modes - different classifications are in use Part 6, lecture 2: Brachytherapy techniques

  48. Low dose rate brachytherapy • The only type of brachytherapy possible with manual afterloading • Most clinical experience available for LDR brachytherapy • Performed with remote afterloaders using 137-Cs or 192-Ir Part 6, lecture 2: Brachytherapy techniques

  49. Low dose rate brachytherapy • Selectron for gynecological brachytherapy • 137-Cs pellets pushed into the applicators using compressed air • 6 channels for up to two parallel treatments Nucletron Part 6, lecture 2: Brachytherapy techniques