Radiation_Protection_in_Radiotherapy.ppt

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1、Radiation Protection inRadiotherapy,Part 13Accidents and Emergencies,IAEA Training Material on Radiation Protection in Radiotherapy,Part 13,lecture 1:Accidents,2,Potential for an Accident in Radiotherapy,Radiotherapy is unique from the point of view of radiation safety,since:it is the only applicati

2、on 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 workersFor patientsFor general public,Part 13,lecture

3、 1:Accidents,4,Potential for accidents,For workersFor patientsFor general public,Part 8Medical ExposurePart 17,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 pe

4、rsons 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 radiotherapyBe able to develop an effective plan for emergencies and accident preventionBe familiar wi

5、th emergency response strategiesTo 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 radiotherapyLecture 2:Emergency preparedness and response,Radiation Protection inRadio

6、therapy,Part 13Accidents and EmergenciesLecture 1:Accidents,IAEA Training Material on Radiation Protection in Radiotherapy,Part 13,lecture 1:Accidents,8,Objectives,Be aware of the potential for accidental radiation exposures affecting patients in radiotherapyAnalyze accidents and be able to define l

7、essons to be learnedBe 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 radiotherapy2.Lessons learned from previous accidents3.Accident prevention,Part 13,lecture 1:Accidents,10,Potential Expos

8、ure,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:A

9、ccidents,11,1.Potential for accidents in radiotherapy,Human error:A therapeutic treatment was delivered to the wrong patientA therapeutic treatment was delivered to the wrong treatment siteA therapeutic treatment was delivered with a substantially different dose or dose fraction to that prescribed b

10、y the medical practitionerEquipment malfunction,Part 13,lecture 1:Accidents,12,Accidents in radiotherapy,We dont have to look far.,Part 13,lecture 1:Accidents,13,A case study.,StaffFive radiation oncologistsTwo medical physicists and one dosimetristFour radiotherapy technologistsTwo shifts from 6 am

11、 to 9 pmTwo 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 dayMultiple fields and beam shaping devices(shielding blocks and wedges)All fields ev

12、ery daySSD technique for multiple fields,Part 13,lecture 1:Accidents,15,The treatment planning system,2 D planningMultidata RTP/2Version 11,installed in 1993Allows for BrachytherapyExternal beamRestriction to four blocks per field,Part 13,lecture 1:Accidents,16,Treatment PlanningEntering blocks sepa

13、rately,Add 1 block Type transmission factor Digitize contourRepeat the procedure with other blocks,Part 13,lecture 1:Accidents,17,The event was triggered,In April 2000 radiation oncologists expressed the demand to use a fifth(central)blockA temporary solution was found to calculate only for the cent

14、ral block Ignoring the other four blocks in the calculation of the dose to specified point,Standard blocks,Additionalblock,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 t

15、he procedure was not writtenAnother physicist entered the data in a similar but slightly different way,Part 13,lecture 1:Accidents,19,Treating 4 blocks as one,Two loops in opposite directions,Part 13,lecture 1:Accidents,20,Treating 4 blocks as one(another way),Two loops in the same direction,Part 13

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

17、e 1:Accidents,22,The discovery of the accident,In November 2000 a radiation oncologist started to observe diarrhoea,which was unusually prolongedIn December 2000 the effect was observed in other patientsThe physicists examined the charts but did not find any abnormality(the computer calculation was

18、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 timesThe treatment was simulated on a water phantom and measurement of doses were made

19、which confirmed higher dose.,Part 13,lecture 1:Accidents,24,Doses to patients were calculated manually,Based on the dose rateThe treatment times from the patients charts,as well as all other treatment parametersSince the fractions were higher than normal,the biologically effective dose and the dose

20、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),As of May 30,2000,Dose Gy,N ofpat.,Part 13,lecture 1:Accidents,26,Part 13,lecture 1:Accidents,27,Results to Date(May 30,2000),8 Deaths of 28

21、patients5 Radiation related2 Unknown.Not enough data1 Due to metastatic cancer20 Surviving patients,Part 13,lecture 1:Accidents,28,Initiating event and contributory factors,The event was triggered byThe search for a way to overcome the limitation of the planning computer(four blocks only)Contributor

22、y factorsThe computer presented the icon as if the blocks were correctly recognizedThe procedure was not testedThe trick“worked”and was time savingIt 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 facto

23、rs(contd),Contributory factors(contd)Procedure not properly documentedTreatment times were longer than usual but no one detected itworkload limited interaction(radiation oncologists,medical physicists and radiotherapy technologists)Computer calculations in general were not verifiedPatient reactions

24、were realized but the follow-up was insufficient,Part 13,lecture 1:Accidents,30,Panama incident summary,2001Minor change of practice in use of a treatment planning systemNot systematically verified16 patients severely overexposed8 patients dead a sobering experience,Part 13,lecture 1:Accidents,31,No

25、t an isolated event,More than 90 cases documentedAffects brachytherapy and external beam radiotherapyAffects developed and developing countries,Part 13,lecture 1:Accidents,32,Major documented accidents in Radiotherapy,Part 13,lecture 1:Accidents,33,Consequences of accidents,Accident may result in a

26、deviation from the intended dose and/or dose distribution:If the dose is too low:impact on cure rateIf the dose is too high,it may have an impact on:,Early(acute)complicationsLate(chronic)complications,Part 13,lecture 1:Accidents,34,Consequences of accidents,External and internal.,Part 13,lecture 1:

27、Accidents,35,Consequences in practice,Dose too low-reduction of tumour control probability.There is no second chance!Dose too high-acute complicationsDose too high-late complications,Part 13,lecture 1:Accidents,36,Accidents in radiotherapy,Horrific consequencesAn opportunity to learnThorough investi

28、gation requiredNot necessarily about blameReporting essentialWhat are the specific issues contributing to accidents in radiotherapy?,Part 13,lecture 1:Accidents,37,Another example,Zaragoza,SpainBreakdown in bending magnet power supplyRepair carried out by a company service technicianNo report made t

29、o Medical Physics before treatment resumedDuring 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 becausenot all accidents are reportedthe frequency o

30、f accidents is likely to vary significantly between different institutionsSome 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 stru

31、ctural shielding is in betweenthere 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,Radiother.Oncol.1992:50 occasions of data transferfrom one point to ano

32、ther for each patient!If one of them is wrong-the overall outcome is affected,Part 13,lecture 1:Accidents,41,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

33、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,42,Early Effects and Clinical Detection of Radiation Accidents,Careful clinical observa

34、tion of patientssignificant reduction in the rate of side-effects can be an indicator of an underdosage accidentincreased complication rate can be an indicator of overdosage accident and of higher expectation for late effects as wellExperienced radiation oncologists may be able to differentiate as l

35、ow as 7-8%differences in dose(with careful weekly patient follow-up),Part 13,lecture 1:Accidents,43,The dose response curve,Is steep for tumor control-5%difference in dose can make 15%difference in cure rateAcute reactions may occur during treatmentThere is a small normal rate of severe complication

36、s-even a small additional number of severe or unusual complications can be significant,Part 13,lecture 1:Accidents,44,2.Lessons learned,No learning without investigationBSS II.29.“Registrants and licensees shall promptly investigate any of the following incidents:(a)any therapeutic treatment deliver

37、ed 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,45,Lessons from Pa

38、nama incident,Awareness in radiotherapy Treatment planning is a critical deviceWritten proceduresTest of new proceduresHand verification of computer calculationsTreatment planning softwaremanual of instructionswarnings on screenfoolproof tests,Part 13,lecture 1:Accidents,46,Lessons(contd),Availabili

39、ty of manufacturer serviceWorkloadPresence and supervision by managersInteraction of professionals,better still to prevent accidents in the first place,3.Accident Prevention,Part 13,lecture 1:Accidents,48,Accident Prevention:Knowing where to start,What can go wrong?What can be the initiating events

40、of accidents?What can be the contributing factors?What measures can be taken for prevention?,Part 13,lecture 1:Accidents,49,“Lessons learned from accidental exposures in radiotherapy”,Part 13,lecture 1:Accidents,50,IAEA Safety Report Series 17,Only reported accidentsTherefore likely bias towards cou

41、ntries with a reporting requirement and structureExternal beam and brachytherapyUnsealed sources(covered in training on Nuclear Medicine),Part 13,lecture 1:Accidents,51,Accidental exposures in external beam RT can be grouped as follows:,Equipment designCalibration of beamsMaintenanceTreatment planni

42、ng and dose calculationSimulationTreatment set-up and delivery,Part 13,lecture 1:Accidents,52,Accidents in EBT,Part 13,lecture 1:Accidents,53,Even before the equipment:facility design(part 7),the possibility of accidental exposure can be minimised by measures such as positioning:the control room and

43、 the equipment within so that staff have a good view of the treatment roompatient and visitor waiting areas so that they are unlikely to enter treatment areas accidentallypatient change areas so that the patient is unlikely to enter a treatment area accidentally,Part 13,lecture 1:Accidents,54,Exampl

44、e:Equipment,Equipment designCalibration of beamsMaintenanceTreatment planning and dose calculationSimulationTreatment set-up and delivery,Part 10Fail to safetyRedundant safety featuresFollow IEC standardsManuals and documentationCommissioning,Part 13,lecture 1:Accidents,55,Example:Calibration,Equipm

45、ent designCalibration of beamsMaintenanceTreatment planning and dose calculationSimulationTreatment set-up and delivery,Part 10Follow appropriate protocolRegular consistency checksIndependent checkAuditsDocumentation,Part 13,lecture 1:Accidents,56,Example:Maintenance,Equipment designCalibration of b

46、eamsMaintenanceTreatment planning and dose calculationSimulationTreatment set-up and delivery,Part 10Good trainingInclude preventative maintenance(PMI)CommunicationFollow manufacturers proceduresDocumentationCheck after each modification,Part 13,lecture 1:Accidents,57,Example:Planning,Equipment desi

47、gnCalibration of beamsMaintenanceTreatment planning and dose calculationSimulationTreatment set-up and delivery,Part 10TrainingIndependent checksQADocumentationParticipation in intercomparisonsIn vivo dosimetry,Part 13,lecture 1:Accidents,58,Example:Simulator,Equipment designCalibration of beamsMain

48、tenanceTreatment planning and dose calculationSimulationTreatment set-up and delivery,Parts 5 and 10Interdisciplinary communicationProtocolsQACommissioning(systematic differences between treatment unit and simulator?),Part 13,lecture 1:Accidents,59,Example:Set-up,Equipment designCalibration of beams

49、MaintenanceTreatment planning and dose calculationSimulationTreatment set-up and delivery,Part 10Portal filmsIn vivo dosimetryTwo people at treatment unitIndependent checksRecord and verify systemDocumentation,Quick Discussion,What would be common features of the strategies to prevent different caus

50、es of accidents in radiotherapy?,Part 13,lecture 1:Accidents,61,Strategies for accident prevention in external beam RT,Quality assuranceIndependent checksGood trainingGood communicationDocumentation.,Part 13,lecture 1:Accidents,62,Strategies for accident prevention in external beam RT,Quality assura