RT13 AE1 Accidents WEB

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Radiation Protection in Radiotherapy: 

Radiation Protection in Radiotherapy Part 13 Accidents and Emergencies IAEA Training Material on Radiation Protection in Radiotherapy

Potential for an Accident in Radiotherapy: 

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

Potential for accidents: 

Potential for accidents For workers For patients For general public

Potential for accidents: 

Potential for accidents For workers For patients For general public Part 8 Medical Exposure Part 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 persons involved - therefore this part is also relevant to these other parts.

Objectives: 

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

Contents: 

Contents Lecture 1: Accidental medical exposure and potential exposure in radiotherapy Lecture 2: Emergency preparedness and response

Radiation Protection in Radiotherapy: 

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

Objectives: 

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

Contents: 

Contents 1. The potential for accidental exposures in radiotherapy 2. Lessons learned from previous accidents 3. Accident prevention

Potential Exposure: 

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.”

1. Potential for accidents in radiotherapy: 

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

Accidents in radiotherapy: 

Accidents in radiotherapy We don’t have to look far...

A case study...: 

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

Workload - a normal radiotherapy department: 

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

The treatment planning system: 

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

Treatment Planning Entering blocks separately: 

Treatment Planning Entering blocks separately Add 1 block Type transmission factor Digitize contour Repeat the procedure with other blocks

The event was triggered: 

The event was triggered 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 Additional block

Overcoming the limitation on the number of blocks: 

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

Slide19: 

Treating 4 blocks as one Two loops in opposite directions

Slide20: 

Treating 4 blocks as one (another way) Two loops in the same direction

Summary : 

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

The discovery of the accident: 

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)

The discovery of the accident: 

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...

Doses to patients were calculated manually: 

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

Number of Patients and their doses (equivalent to 2 Gy/fraction): 

Number of Patients and their doses (equivalent to 2 Gy/fraction) As of May 30, 2000 Dose [Gy] N of pat.

Results to Date (May 30, 2000): 

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

Initiating event and contributory factors: 

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

Initiating event and contributory factors (cont’d): 

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

Panama incident summary: 

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

Not an isolated event: 

Not an isolated event More than 90 cases documented Affects brachytherapy and external beam radiotherapy Affects developed and developing countries

Major documented accidents in Radiotherapy: 

Major documented accidents in Radiotherapy

Consequences of accidents: 

Consequences of accidents 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: 

Consequences of accidents External and internal...

Consequences in practice: 

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

Accidents in radiotherapy: 

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?

Another example: 

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

Frequency of accidents: 

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)

Potential for accidental medical exposure in Radiotherapy: 

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. )

Slide40: 

Radiother. Oncol. 1992: > 50 occasions of data transfer from one point to another for each patient! If one of them is wrong - the overall outcome is affected

Potential for an Accident in Radiotherapy: 

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

Early Effects and Clinical Detection of Radiation Accidents: 

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)

The dose response curve: 

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

2. Lessons learned: 

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;”

Lessons from Panama incident: 

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

Lessons (cont’d): 

Lessons (cont’d) Availability of manufacturer service Workload Presence and supervision by managers Interaction of professionals

…better still to prevent accidents in the first place: 

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

Accident Prevention: Knowing where to start: 

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?

“Lessons learned from accidental exposures in radiotherapy”: 

“Lessons learned from accidental exposures in radiotherapy”

IAEA Safety Report Series 17: 

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)

Accidental exposures in external beam RT can be grouped as follows:: 

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

Accidents in EBT: 

Accidents in EBT

Even before the equipment: facility design (part 7): 

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 the equipment within so that staff have a good view of the treatment room patient and visitor waiting areas so that they are unlikely to enter treatment areas accidentally patient change areas so that the patient is unlikely to enter a treatment area accidentally

Example: Equipment: 

Example: Equipment Equipment design Calibration of beams Maintenance Treatment planning and dose calculation Simulation Treatment set-up and delivery Part 10 Fail to safety Redundant safety features Follow IEC standards Manuals and documentation Commissioning

Example: Calibration: 

Example: Calibration Equipment design Calibration of beams Maintenance Treatment planning and dose calculation Simulation Treatment set-up and delivery Part 10 Follow appropriate protocol Regular consistency checks Independent check Audits Documentation

Example: Maintenance: 

Example: Maintenance Equipment design Calibration of beams Maintenance Treatment planning and dose calculation Simulation Treatment set-up and delivery Part 10 Good training Include preventative maintenance (PMI) Communication Follow manufacturers procedures Documentation Check after each modification

Example: Planning: 

Example: Planning Equipment design Calibration of beams Maintenance Treatment planning and dose calculation Simulation Treatment set-up and delivery Part 10 Training Independent checks QA Documentation Participation in intercomparisons In vivo dosimetry

Example: Simulator: 

Example: Simulator Equipment design Calibration of beams Maintenance Treatment planning and dose calculation Simulation Treatment set-up and delivery Parts 5 and 10 Interdisciplinary communication Protocols QA Commissioning (systematic differences between treatment unit and simulator?)

Example: Set-up: 

Example: Set-up Equipment design Calibration of beams Maintenance Treatment planning and dose calculation Simulation Treatment set-up and delivery Part 10 Portal films In vivo dosimetry Two people at treatment unit Independent checks Record and verify system Documentation

Quick Discussion: 

Quick Discussion What would be common features of the strategies to prevent different causes of accidents in radiotherapy?

Strategies for accident prevention in external beam RT: 

Strategies for accident prevention in external beam RT Quality assurance Independent checks Good training Good communication Documentation ...

Strategies for accident prevention in external beam RT: 

Strategies for accident prevention in external beam RT Quality assurance Independent checks Good training Documentation Can they also be applied to brachytherapy???

An Accident with Remote Afterloading: 

An Accident with Remote Afterloading Area monitor giving an alarm - assumed faulty In fact, the source wire was broken and the source was still in the patient Patient returned to ward Received 16,000 Gy at 1 cm instead of the planned 18 Gy! Patient died!

Accidental exposures for brachy-therapy can be grouped as follows: 

Accidental exposures for brachy-therapy can be grouped as follows Equipment design Source order and delivery Source calibration and acceptance Source preparation for the treatment Treatment planning and dose calculation Source removal

Accidents in Brachytherapy: 

Accidents in Brachytherapy

Note: 

Note Considering the number of patients treated, the relative number of accidents in brachytherapy is approximately 10 times higher than in EBT Treatment planning and source calibration are the most important factors in both Issues related to the radioactive source are important in brachytherapy

Issues for accidents in brachytherapy: 

Issues for accidents in brachytherapy Equipment design Source order and delivery Source calibration and acceptance Source preparation for the treatment Treatment planning and dose calculation Source removal Part 11, compare also comments on EBT Authorization Transport Record keeping Handling of sources - equipment Accounting of sources Disposal, discharge of patients

Accident prevention: General features: 

Accident prevention: General features Training, training, training Defence in depth Documentation Emergency equipment Quality Assurance system

Accident Prevention: Training: 

Accident Prevention: Training Radiotherapy physics (calibration), maintenance, radiation oncologists, technologists, nurses for brachytherapy Specific training use of the machine, including not only radiation equipment but also treatment planning system. Include training to detect and deal with unusual events and situations Reassessment of needs for staff and training as patient workload increases and each time a new equipment or technique is introduced.

Education and training: 

Education and training Following the national or regional recommendations by professional societies The education and training of the various professionals has to include case histories of accidents and their prevention Informative lecturers on cases histories and accident prevention should also be addressed to the hospital managers

Accident Prevention: Defence-in-depth : 

Accident Prevention: Defence-in-depth IAEA Safety Fundamentals (SS 120, 1996): “The application of more than a single protection measure for a given safety objective such that the objective is achieved even if one of the protective measures fails.” e.g.: redundant and independent calibration, external audits, in vivo dosimetry, participation in TLD postal services

Accident Prevention: 

Accident Prevention Defence-in-depth (independent verification) applied to radiotherapy could have prevented all reported major accidents related to the commissioning of a new beam (calibration) or a TPS

Defence in depth: 

Defence in depth An example of possible defence-in-depth steps available for calibration of a 60-Co unit: 1. Formal procedure for calibration of the new beam 2. Check of consistency between the measured dose rate and the certificate of the radiation source 3. Another person determines the dose rate independently before starting patients’ treatments

Defence in depth: 

Defence in depth Co-60 teletherapy unit calibration (cont’d): 4. Use of IAEA/WHO TLD Postal Dose Check Service 5. Periodic re-measurements of the beam and comparison with decay 6. External audits 7. Close observation of patients for side effects and complications A Quality Assurance programme has to integrate sufficient defence in depth

An example of defence-in-depth for maintenance:: 

An example of defence-in-depth for maintenance: 1. Maintenance strategy condition to authorize import of equipment 2. Training of maintenance engineers on that particular model of equipment and of the consequences of misadjustment of physical parameters (including accident case histories) 3. Formal transfer of the equipment for maintenance and back to the medical physicist 4. Test of the equipment before resuming treatments 5. Training of the staff to identify displays and conflicting signals 6. Equipment design preventing “beam on” when interlocks or selectors disabled

Accident prevention (cont’d): 

Accident prevention (cont’d) Organization Sufficient staff following recommendations on staffing (professional societies) Well defined functions and responsibilities Review of staffing, responsibilities and training as workload increases or new equipment or techniques are introduced

Accident prevention: 

Accident prevention Communication Communication procedures for safety critical issues Recording and reporting of treatments following protocols Prompt reporting of any unexpected behavior of a machine Prompt reporting of unexpected reaction of a patient or of a series of patients

Accident Prevention: Documentation: 

Accident Prevention: Documentation Processes and data Formal commissioning for ALL equipment - documentation Formal equipment transfer for maintenance Written documentation Minutes of meetings - signed and approved Keep important information in duplicate (e.g. beam data should be kept in two different locations)

Written Procedures: 

Written Procedures available to relevant persons concise instructions specify immediate action identify responsible persons drawings and diagrams useful flowcharts

Example: 60-Co source jam...: 

Example: 60-Co source jam...

Accident prevention: 

Accident prevention ICRP 86: Checklists

Emergency Equipment: 

Emergency Equipment Manual, procedures, documentation Radiation monitor Other items as required by the specific application, e.g.: spill kit emergency lead container blood collection (for biological monitoring)

Accident prevention: QA: 

Accident prevention: QA All previous items integrated into a QA program Compare also part 12 of the course

Accident Prevention: 

Accident Prevention Of importance are also: 1) regulatory requirements, 2) managerial responsibilities and measures, 3) ensuring that measures are observed by each staff involved and, Training on accident prevention for health authorities and hospital managers and all staff ‘on shop floor’

Dissemination of information within professional community: 

Dissemination of information within professional community A chance to learn Make sure legal investigations are not interfered with Make sure no one can be identified

Lessons learned : Summary: 

Lessons learned : Summary Adherence to established safety procedures would have prevented most accidents Systematic audits by management help to ensure that level of knowledge and performance of staff is maintained A poor safety culture can result in degradation of safety systems and procedures Deficient training is contributory in the majority of accidents

Where to get more information: 

Where to get more information Cosset JM. Irradiation accidents – lessons for oncology? Radiother. Oncol. 63: 1-10, 2002 International Atomic Energy Agency. Lessons learned from accidental exposures in radiotherapy. Safety Report Series: N17. 2000. International Commission on Radiological Protection. Prevention of Accidental Exposures to patients undergoing radiation therapy, ICRP report 86. Oxford: Pergamon Press; 2001.

Any questions?: 

Any questions?

Question:: 

Question: Assume the following scenario: A shielding block has been omitted for the eye of a patient treated with external beam therapy for one day. Please discuss: The consequences for the patient The actions to be taken Methods to prevent this accident happening in the future

Acknowledgment: 

Acknowledgment Pedro Ortiz López, IAEA Modupe Oresegun, IAEA

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