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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 13 Accidents and Emergencies

  2. Potential for an Accident in Radiotherapy • Radiotherapy is unique from the point of view of radiation safety, since: • it is the only application of radiation sources in which very high doses are given on purpose to a part of a human body • not only the tumour - normal tissue also receives doses comparable with the dose to the tumour Part 13, lecture 1: Accidents

  3. Potential for accidents • For workers • For patients • For general public Part 13, lecture 1: Accidents

  4. For workers For patients For general public Part 8 Medical Exposure Part 17 Potential for accidents While accidents affecting workers and general public are covered in other parts of the course, some aspects of dealing with an accident and/or an emergency are independent of the group of persons involved - therefore this part is also relevant to these other parts. Part 13, lecture 1: Accidents

  5. Objectives • Be aware of the potential for accidental radiation exposures affecting patients in radiotherapy • Be able to develop an effective plan for emergencies and accident prevention • Be familiar with emergency response strategies • To identify the information which needs to be reported in case of an emergency Part 13, lecture 1: Accidents

  6. Contents • Lecture 1: Accidental medical exposure and potential exposure in radiotherapy • Lecture 2: Emergency preparedness and response Part 13, lecture 1: Accidents

  7. Radiation Protection inRadiotherapy IAEA Training Material on Radiation Protection in Radiotherapy Part 13 Accidents and Emergencies Lecture 1: Accidents

  8. Objectives • Be aware of the potential for accidental radiation exposures affecting patients in radiotherapy • Analyze accidents and be able to define lessons to be learned • Be able to develop an effective plan for prevention of accidental exposures Part 13, lecture 1: Accidents

  9. Contents 1. The potential for accidental exposures in radiotherapy 2. Lessons learned from previous accidents 3. Accident prevention Part 13, lecture 1: Accidents

  10. Potential Exposure • IAEA Safety Series 120 and glossary of BSS: “ Exposure that is not expected with certainty to be delivered but that may result from an accident at a source or owing to an event or a sequence of events of a probabilistic nature, including equipment failures and operating errors.” Part 13, lecture 1: Accidents

  11. 1. Potential for accidents in radiotherapy • Human error: • A therapeutic treatment was delivered to the wrong patient • A therapeutic treatment was delivered to the wrong treatment site • A therapeutic treatment was delivered with a substantially different dose or dose fraction to that prescribed by the medical practitioner • Equipment malfunction Part 13, lecture 1: Accidents

  12. Accidents in radiotherapy • We don’t have to look far... Part 13, lecture 1: Accidents

  13. A case study... • Staff • Five radiation oncologists • Two medical physicists and one dosimetrist • Four radiotherapy technologists • Two shifts from 6 am to 9 pm • Two radiation oncologists (one in the morning and one in the evening) in Hospital Arosemena on a monthly rotation Part 13, lecture 1: Accidents

  14. Workload - a normal radiotherapy department • 70 to 80 patients per day • Multiple fields and beam shaping devices (shielding blocks and wedges) • All fields every day • SSD technique for multiple fields Part 13, lecture 1: Accidents

  15. The treatment planning system • 2 D planning • Multidata RTP/2 • Version 11, installed in 1993 • Allows for • Brachytherapy • External beam • Restriction to four blocks per field Part 13, lecture 1: Accidents

  16. Treatment PlanningEntering blocks separately • Add 1 block • Type transmission factor • Digitize contour • Repeat the procedure with other blocks Part 13, lecture 1: Accidents

  17. The event was triggered Additional block • In April 2000 radiation oncologists expressed the demand to use a fifth (central) block • A temporary solution was found to calculate only for the central block • Ignoring the other four blocks in the calculation of the dose to specified point Standard blocks Part 13, lecture 1: Accidents

  18. Overcoming the limitation on the number of blocks • In August 2000 one physicist came up with another solution: to enter several blocks at once. • BUT the procedure was not written • Another physicist entered the data in a similar but slightly different way Part 13, lecture 1: Accidents

  19. Computer calculates correct treatment time Treating 4 blocks as one Two loops in opposite directions Part 13, lecture 1: Accidents

  20. Computer accepts input and calculates wrong treatment time by about + 100 % (for 5% transmission factor of the blocks) Treating 4 blocks as one (another way) Two loops in the same direction Part 13, lecture 1: Accidents

  21. Summary • The treatment time was approximately twice • Example: similar treatment on another patients 0.6 min (one field) as compared with more than 1.2 min • The computer printout provides distorted isodoses and the longer treatment time but the icon with the four blocks Part 13, lecture 1: Accidents

  22. The discovery of the accident • In November 2000 a radiation oncologist started to observe diarrhoea, which was unusually prolonged • In December 2000 the effect was observed in other patients • The physicists examined the charts but did not find any abnormality (the computer calculation was not questioned) Part 13, lecture 1: Accidents

  23. The discovery of the accident • In March 2001 the isodoses and the treatment time were reexamined closer and found differences in isodose shape and different treatment times • The treatment was simulated on a water phantom and measurement of doses were made which confirmed higher dose... Part 13, lecture 1: Accidents

  24. Doses to patients were calculated manually • Based on the dose rate • The treatment times from the patients’ charts, as well as all other treatment parameters • Since the fractions were higher than normal, the biologically effective dose and the dose equivalent to a treatment of 2 Gy/fraction were also calculated Part 13, lecture 1: Accidents

  25. Number of Patients and their doses (equivalent to 2 Gy/fraction) N of pat. As of May 30, 2000 Dose [Gy] Part 13, lecture 1: Accidents

  26. Part 13, lecture 1: Accidents

  27. Results to Date (May 30, 2000) • 8 Deaths of 28 patients • 5 Radiation related • 2 Unknown. Not enough data • 1 Due to metastatic cancer • 20 Surviving patients Part 13, lecture 1: Accidents

  28. Initiating event and contributory factors • The event was triggered by • The search for a way to overcome the limitation of the planning computer (four blocks only) • Contributory factors • The computer presented the icon as if the blocks were correctly recognized • The procedure was not tested • The trick “worked” and was time saving • It was claimed that, in another TPS in Panama the same way of data entry works well Part 13, lecture 1: Accidents

  29. Initiating event and contributory factors (cont’d) • Contributory factors (cont’d) • Procedure not properly documented • Treatment times were longer than usual but no one detected it • workload • limited interaction (radiation oncologists, medical physicists and radiotherapy technologists) • Computer calculations in general were not verified • Patient reactions were realized but the follow-up was insufficient Part 13, lecture 1: Accidents

  30. Panama incident summary • 2001 • ‘Minor’ change of practice in use of a treatment planning system • Not systematically verified • 16 patients severely overexposed • 8 patients dead • … a sobering experience Part 13, lecture 1: Accidents

  31. Not an isolated event • More than 90 cases documented • Affects brachytherapy and external beam radiotherapy • Affects developed and developing countries Part 13, lecture 1: Accidents

  32. Major documented accidents in Radiotherapy Part 13, lecture 1: Accidents

  33. Accident may result in a deviation from the intended dose and/or dose distribution: If the dose is too low: impact on cure rate If the dose is too high, it may have an impact on: Early (acute) complications Late (chronic) complications Consequences of accidents Part 13, lecture 1: Accidents

  34. Consequences of accidents External and internal... Part 13, lecture 1: Accidents

  35. Consequences in practice • Dose too low - reduction of tumour control probability. There is no second chance! • Dose too high - acute complications • Dose too high - late complications Part 13, lecture 1: Accidents

  36. Accidents in radiotherapy • Horrific consequences • An opportunity to learn • Thorough investigation required • Not necessarily about blame • Reporting essential • What are the specific issues contributing to accidents in radiotherapy? Part 13, lecture 1: Accidents

  37. Another example • Zaragoza, Spain • Breakdown in bending magnet power supply • Repair carried out by a company service technician • No report made to Medical Physics before treatment resumed • During the next 10 days, 27 patients were treated with electron beams having dose rates of between 3 to 7 times above the expected Part 13, lecture 1: Accidents

  38. Frequency of accidents • Difficult to estimate because • not all accidents are reported • the frequency of accidents is likely to vary significantly between different institutions • Some estimate in ICRU report 24 (1976) Part 13, lecture 1: Accidents

  39. Potential for accidental medical exposure in Radiotherapy • the patient is directly in the beam or sealed sources are placed in contact with the tissue: no structural shielding is in between • there are a large number of steps from the prescription of the treatment to the delivery of the dose (compare G Leunens et al.: “Garbage in Garbage out” Radiother. Oncol. ) Part 13, lecture 1: Accidents

  40. Potential for an Accident in Radiotherapy • many records and communications are involved in those steps, between different professionals and even with the patient • there is a combination of very different activities from the very manual (such as tailored organ shielding preparation in the workshop), to very sophisticated computer assisted techniques and high technology equipment Part 13, lecture 1: Accidents

  41. Early Effects and Clinical Detection of Radiation Accidents • Careful clinical observation of patients • significant reduction in the rate of side-effects can be an indicator of an underdosage accident • increased complication rate can be an indicator of overdosage accident and of higher expectation for late effects as well • Experienced radiation oncologists may be able to differentiate as low as 7-8 % differences in dose (with careful weekly patient follow-up) Part 13, lecture 1: Accidents

  42. The dose response curve • Is steep for tumor control - 5% difference in dose can make 15% difference in cure rate • Acute reactions may occur during treatment • There is a small normal rate of severe complications - even a small additional number of severe or unusual complications can be significant Part 13, lecture 1: Accidents

  43. 2. Lessons learned • No learning without investigation • BSS II.29. “Registrants and licensees shall promptly investigate any of the following incidents: (a) any therapeutic treatment delivered to either the wrong patient or the wrong tissue, or using the wrong pharmaceutical, or with a dose or dose fractionation differing substantially from the values prescribed by the medical practitioner or which may lead to undue acute secondary effects;” Part 13, lecture 1: Accidents

  44. Lessons from Panama incident • Awareness in radiotherapy • Treatment planning is a critical device • Written procedures • Test of new procedures • Hand verification of computer calculations • Treatment planning software • manual of instructions • warnings on screen • foolproof tests Part 13, lecture 1: Accidents

  45. Lessons (cont’d) • Availability of manufacturer service • Workload • Presence and supervision by managers • Interaction of professionals Part 13, lecture 1: Accidents

  46. …better still to prevent accidents in the first place 3. Accident Prevention

  47. Accident Prevention: Knowing where to start • What can go wrong? • What can be the initiating events of accidents? • What can be the contributing factors? • What measures can be taken for prevention? Part 13, lecture 1: Accidents

  48. “Lessons learned from accidental exposures in radiotherapy” Part 13, lecture 1: Accidents

  49. IAEA Safety Report Series 17 • Only reported accidents • Therefore likely bias towards countries with a reporting requirement and structure • External beam and brachytherapy • Unsealed sources (covered in training on Nuclear Medicine) Part 13, lecture 1: Accidents

  50. Accidental exposures in external beam RT can be grouped as follows: • Equipment design • Calibration of beams • Maintenance • Treatment planning and dose calculation • Simulation • Treatment set-up and delivery Part 13, lecture 1: Accidents