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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. Radiation Protection inRadiotherapy IAEA Training Material on Radiation Protection in Radiotherapy Part 4 Principles of Radiation Protection

  2. The two aims of radiation protection 1. Prevention of deterministic effects (except in radiotherapy those that are intentionally produced, but including those which are NOT intended, such as accidental medical exposure) 2. Reduction of the probability of stochastic effects Part 4, lecture 1: General principles

  3. The need for protection applies to all dose levels • It is generally assumed that even very small doses of ionizing radiation can potentially be harmful (linear no threshold hypothesis) • Therefore, persons must be protected from ionizing radiation at all dose levels Part 4, lecture 1: General principles

  4. Objectives • Appreciate the need for radiation protection • Be familiar with the recommendations of the ICRP and the requirements of the IAEA BSS • Appreciate the fundamental principles of justification, optimization and dose limitation in radiological protection • Understand the importance of the BSS in the context of radiation protection in radiotherapy Part 4, lecture 1: General principles

  5. Contents Lecture 1: Basic Principles of Radiation Protection Lecture 2: The Basic Safety Standards (BSS) of the IAEA (1996) Part 4, lecture 1: General principles

  6. Radiation Protection inRadiotherapy IAEA Training Material: Radiation Protection in Radiotherapy Part 4 Principles of Radiation Protection Lecture 1: General Principles

  7. Objectives • Appreciate the need for radiation protection • Be familiar with the recommendations of the ICRP • Appreciate the fundamental principles of justification, optimization and dose constraints • Be able to apply very basic radiation protection principles to the radiotherapy environment Part 4, lecture 1: General principles

  8. Contents 1. The ICRP recommendations 2. Basic principles • Justification • Optimization • Dose limitation 3. Time, distance, shielding Part 4, lecture 1: General principles

  9. The International Commission on Radiological Protection • A group of recognized leaders in the field of radiation protection • established 1928 (by the International Congress of Radiology ICR) • concerned with the protection of humans from ionizing radiation • official relationships with WHO, IAEA, ICRU • convenes task groups of experts to address particular issues • issues reports and recommendations Part 4, lecture 1: General principles

  10. Recommendations of the ICRP • Prepared typically by a task group which includes other experts • Approved by the full commission • Published in the journal “Annals of the ICRP” • Have no legislative mandate themselves - however, are typically the foundation onto which national legislation is built Part 4, lecture 1: General principles

  11. Important ICRP reports for the present course · ICRP. Protection against ionising radiation from external sources used in medicine, ICRP report 33. Oxford: Pergamon Press; 1982. · ICRP. Protection of the patient in radiotherapy, ICRP report 44. Oxford: Pergamon Press; 1985. · ICRP. Radiological Protection and Safety in Medicine, ICRP report 73. Oxford: Pergamon Press; 1996. · ICRP. Radiological Protection and Safety and pregnancy, ICRP report 73. Oxford: Pergamon Press; 1996. · ICRP. Protection from potential exposures: application to selected radiation sources, ICRP report 76. Oxford: Pergamon Press; 1997. · ICRP. Prevention of accidental exposures to patients undergoing radiation therapy, ICRP report 86. Oxford: Pergamon Press; 2002. Part 4, lecture 1: General principles

  12. Essential reading ICRP. The 1990 recommendations of the International Commission on Radiological Protection, ICRP report 60. Oxford: Pergamon Press; 1991.

  13. The ICRP Recommendations • ICRP publication 60 - 1990 • The recommended system of radiation protection is based upon 3 principles: • Benefit of a practice must offset the radiation detriment • Exposures and likelihood of exposure should be kept as low as reasonably achievable, economic and social factors being taken into account • Dose limits should be set to ensure that no individual faces an unacceptable risk in normal circumstances Part 4, lecture 1: General principles

  14. “ICRP 60” • Weighs all existing data to arrive at quantitative recommendations for risk, detriment, dose and dose rate weighting factors • Considers exposure to humans only • Considers exposure in three categories: occupational, medical, public Part 4, lecture 1: General principles

  15. IAEA BSS (1996) - glossary • Occupational exposure • “All exposures of workers incurred in the course of their work, with the exception of exposures excluded from the Standards and exposures from practices or sources exempted by the Standards.” Part 4, lecture 1: General principles

  16. IAEA BSS (1996) - glossary • Medical exposure • “Exposure incurred by patients as part of their own medical or dental diagnosis or treatment; by persons, other than those occupationally exposed, knowingly while voluntarily helping in the support and comfort of patients; and by volunteers in a programme of biomedical research involving their exposure.” Part 4, lecture 1: General principles

  17. IAEA BSS (1996) - glossary • Public exposure • “Exposure incurred by members of the public from radiation sources, excluding any occupational or medical exposure and the normal local natural background radiation but including exposure from authorized sources and practices and from intervention situations.” Part 4, lecture 1: General principles

  18. 2. Fundamental principles of radiation protection • Justification of practices • Limitation of doses • Optimization of protection and safety Part 4, lecture 1: General principles

  19. 2. Fundamental principles of radiation protection • Justification of practices • Limitation of doses* • Optimization of protection and safety *no dose limitation applies to medical exposure - however, both justification and optimization are essential Part 4, lecture 1: General principles

  20. Time for Discussion Justification Optimization What do the three principles imply to you? Dose limitation

  21. Justification • No use of ionizing radiation is justified if there is no benefit • All applications must be justified • This implies: All, even the smallest exposures are potentially harmful and the risk must be offset by a benefit Part 4, lecture 1: General principles

  22. Risk/Benefit analysis • Need to evaluate the benefits of radiation - an easy task in the case of radiotherapy • Radiation is the therapeutic agent • Assessment of the risks requires the knowledge of the dose received by persons Part 4, lecture 1: General principles

  23. Optimization • When radiation is to be used then the exposure should be optimized to minimize any possibility of detriment. • Optimization is “doing the best you can under the prevailing conditions” • Need to be familiar with techniques and options to optimize the application of ionizing radiation - this is really the main objective of the present course Part 4, lecture 1: General principles

  24. Optimization in the context of radiotherapy • Two aspects: • Optimization of the dose to the target = MAXIMIZATION of dose • Optimization of protection • of the staff (part 8 of the present course) • of the patient (parts 9 to 13) • of the public (part 17) • Only the second aspect is objective of radiation protection Part 4, lecture 1: General principles

  25. A comment on the optimization of patient protection • Optimization of treatment is primary objective of radiotherapy • This includes: • optimizing the dose distribution to the target • reduction of possibility of severe side effects by minimizing the dose to other structures • accident prevention Part 4, lecture 1: General principles

  26. Optimization • Must take into account the resources available - this includes economic circumstances • Often a tricky question - where shall we stop, how much shielding should we really use? Part 4, lecture 1: General principles

  27. Optimization principle Part 4, lecture 1: General principles

  28. …very much in line with the rest of real life • Both justification and optimization are part of all strategies when handling potentially harmful substances or dealing with risks: • there must be a benefit • the risk should be kept as low as possible • Same for household chemicals, drugs, traffic, travel, sports, …. Part 4, lecture 1: General principles

  29. A comment on optimization (as low as reasonably achievable) • Issues which are often subject of discussion: • L … what is a low dose? • R … what is reasonable? Part 4, lecture 1: General principles

  30. What is low? • It can be very costly to consider every dose level explicitly • Discussions are on-going about dose levels below ‘regulatory concern’ • A potential starting point are doses from natural background which are inevitable and one can assume organisms have adapted to them Part 4, lecture 1: General principles

  31. Average annual doses in mSv from natural sources in European countries Part 4, lecture 1: General principles

  32. What is Radon (222Rn) ? • It is a radioactive gas that exists everywhere in the atmosphere • It is a member of the 238U series • It is formed by the decay of 226Ra Part 4, lecture 1: General principles

  33. What is Radon (222Rn) ? • Half-life 3.82 days • It is an alpha emitter decaying to 218Po • 218Po is also an alpha emitter (T½ 3 min) • Other important decay products are 214Po (a, T½ 0.164 msec) and 214Bi (b, T½ 19.9 min) Part 4, lecture 1: General principles

  34. The hazard arises from the inhalation of its decay products which are not gaseous Most of the decay products become attached to aerosols in the atmosphere and are deposited in the conducting airways and in the lung during respiration. Why is Radon a Problem? Part 4, lecture 1: General principles

  35. Other important contributions to natural exposure: Potassium-40 • 40K constitutes 120 parts per million of stable potassium which is an essential trace element in every human body • 40K has a half-life of 1.28 x 109 years, decaying by beta emission (Emax 1.3 MeV) • An 80 kg adult male contains about 180 g of potassium -> 18 mg of 40K • This gives an annual internal effective dose of 170 µSv Part 4, lecture 1: General principles

  36. The cosmic ray contribution to the background radiation varies markedly with altitude. Note, that at cruising altitude in a Boeing 747 the dose rate is approximately 5 mSv/h Part 4, lecture 1: General principles

  37. Average Background DosesUNSCEAR 2000 Report WORLDWIDE AVERAGE DOSES Source Effective dose Typical range (mSv per year) (mSv per year) External exposure • Cosmic rays 0.4 0.3-1.0 • Terrestrial gamma rays 0.5 0.3-0.6 Internal exposure • Inhalation 1.2 0.2-10 • Ingestion 0.3 0.2-0.8 Total 2.4 1–10 Part 4, lecture 1: General principles

  38. What is ‘reasonable’? • Depends on ‘prevailing conditions’ including • economic • cultural • May be different for different individuals, however the risk/benefit analysis made in parts 3 and 6 of the course provides a rational basis Part 4, lecture 1: General principles

  39. Dose limitation • No dose limitation for medical exposure of the patient - it is always assumed that the benefits for the patient outweigh the risks • Limits need to be applied for public and occupational exposures. Part 4, lecture 1: General principles

  40. Limits and constraints • Dose limits are one of the three principles of protection as introduced by ICRP and BSS. Fixed dose limits are recommended by ICRP and often enforced by a national legal process (Radiation Protection Legislation). • Dose constraints are used in an optimization process to guide planning. Constraints and the importance thereof may be subject to change to achieve the optimum solution to a problem (Best practice guidelines). Part 4, lecture 1: General principles

  41. Optimization and dose limitation • It is NOT the aim to get close to the limit values - the aim is to get as low as reasonably achievable • Is part of risk management • Keeps the risks of dealing with ionizing radiation of the same order as other risks Part 4, lecture 1: General principles

  42. If radiation is justified, how do we optimize the exposure and do not exceed dose limits? … this is the objective of practical radiation protection

  43. 3. Basic radiation protection strategies • Radiation cannot be seen, heard or felt. Therefore it is essential to know about it. • Can be accurately measured using appropriate instruments • Need appropriately qualified expert Smart Ion from Mini-Instruments Part 4, lecture 1: General principles

  44. Basic radiation protection strategies • Radiation cannot be seen, heard or felt. Therefore it is essential to know about it. • Need signs and interlocks Part 4, lecture 1: General principles

  45. Basic radiation protection strategies • Hazard Reduction Methods: • Time • Distance • Shielding Part 4, lecture 1: General principles

  46. Time Dose is proportional to the time exposed Dose = Dose-rate x Time Part 4, lecture 1: General principles

  47. Consequence • Reduce time in contact with radiation sources as much as compatible with the task • Training of a particular task using non-radioactive dummy sources helps Part 4, lecture 1: General principles

  48. Distance Inverse square law (ISL): dose-rate distance Dose-rate  1/(distance)2 Part 4, lecture 1: General principles

  49. Example from brachytherapy Part 4, lecture 1: General principles

  50. Consequence • Distance is very efficient for radiation protection as the dose falls off in square (compare also part 2 of the course) • Examples: • long tweezers for handling of sources • big bunkers for radiation equipment Part 4, lecture 1: General principles