1 / 9

ACCIDENTAL MEDICAL EXPOSURE

veru useful

SHALIN1
Download Presentation

ACCIDENTAL MEDICAL EXPOSURE

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 10-05-2023 Who are the people affected by the accidents in Radiation Therpay? IAEA Post Graduate Educational Course on Radiation Protection and Safe Use of Radiation Sources Part VIII:Medical Exposures in Radiotherapy 1. Members of the general public – irradiated as a result of failure of implementation of radiation protection and safety rules Clinical staff – Irradiated during preparation of radiation sources or patient treatment or during installation, repairs, source change, or other equipment servicing; Patient injured during treatment 2. VIII.5 – Accidental medical exposures 3. The main focus in this lecture will be on the third group I.e accidental exposure to patient during treatment Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 4 Possible Radiation Accidents that could lead to exposure of General Public & Clinical Staff This lecture will cover 1. 2. Loss of a radioactive source Loss or damage to the shielding of a radiation source Loss of containment causing a major spill or release of radioactivity Unintentional exposure of part or all of the body to a radiation beam Unintentional radioactive contamination of part or all of the body. • Types of Radiation emergencies • Radiation accident in Radiation therapy treatment • Potential for radiation emergency in Radiotherapy • Case studies of Radiation accidents in External beam therapy • Case studies – Radiation Accidents in Brachytherapy 3. 4. 5. Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 2 Slide 5 What is Radiation Accident in Radiotherpay? What is an accidental exposure to Radiotherapy patients? • In Radiotherapy, a ‘normal’ radiation exposure is a treatment that closely follows the plan specified in the treatment prescription. An accidental exposure can therefore be considered to have occurred if there is a substantial deviation from the prescription • Doses significantly below that prescribed can have severe consequences to the patient and may constitute an accident • A radiation accident is an unintended event that has or may have adverse consequences. • This could be – Operator error – human error – Equipment failure – Any other mishap - ICRP Publication 86 Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 3 Slide 6 1

  2. 10-05-2023 Why to bother about excess radiation to Radiotherpy patient? Classification of Radiation Accidents • Very high doses are delivered to the patient (20Gy to 80Gy) and this is decided by the tolerance dose to normal tissues and hence any accidental over exposure could have adverse consequences • Radiation beam is focused on to the patient or radioactive sources are inserted in to the patient body and any mistake in these could have negative impact on the patient treatment , some times even lead to death of the patient. Radiation accidents in Radiotherapy Events relating to Equipment Events relating to Individual patient Affects many patients Affects only that patient Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 7 Slide 10 Which equipments’ malfunction cold potentially affect the treatment? Potential for an accident in Radiotherapy • A radiotherapy treatment, from prescription to delivery is a very complex process. • It involves many professionals, a number of steps and several treatment sessions with many variable parameters. • A radiotherapy technologist may be required to treat some 50 patients a day, for which the parameters are similar and yet different from one patient to the next, often with personalized ancillary devices. • Radiation Measuring instruments – Calibration of teletherapy units • Treatment simulator • Treatment planning system – Incorrect input, lack of understanding of algorithm • Treatment machine – Malfunction of interlocks Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 8 Slide 11 Where and how the dosimeter can go wrong? Potential for an accident in Radiotherapy Incidents involving measuring system 1. Incorrect use of calibration factor of the reference dosimeter 2. Wrong inter-comparison with the secondary system 3. Error in routine use of dosimeter • Because of this complexity of equipment, techniques and procedures, there is considerable scope for errors and mistakes and it may not be possible to compensate for an error in under or over exposure. • Given the complexity of radiotherapy and its sensitivity to errors and mistakes, nothing should be left to chance, but rather, a structured and systematic approach is needed. • Defense in Depth should be the concept Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 9 Slide 12 2

  3. 10-05-2023 Can the Treatment planning system go wrong? Radiation Incidents resulting from incorrect dose calibration – Case Study II • Incorrect input data • Misunderstanding the algorithm • Inadequate training • Incident: Incorrect side of the parallel plate chamber was used for calibration of electron beam • Cause : Due to a label indicating the side to be exposed pasted wrongly • Consequence: – 6MeV 20% overdose – 9MeV 10% overdose – 12MeV 8% overdose • TLD inter-comparison reveled the error • Action Taken: Calibration repeated Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 13 Slide 16 Where could we go wrong with the treatment machine? Radiation Incidents resulting from incorrect dose calibration – Case Study III • Incident: Wrong value for pressure was used during output calibration of a cobalt unit in a hill station (1000m above sea level) • Consequence: – Patients were overdosed upto 21% • Cause: – No barometer was available to measure pressure – Value of pressure was obtained form airport which was corrected for sea level • Commissioning or acceptance testing • Calibration of the unit • Constancy check (daily, weekly) • Malfunction of the machine • Incorrect use of the machine Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 14 Slide 17 Radiation Incidents resulting from incorrect dose calibration – Case Study I How does reading the pressure wrong affect the dose? KTP= (273.2+T) Po / (273.2+To)P Where T & P are the Temperature & Pressure during measurement; To & Po are the Temperature & Pressure at reference condition (usually 760mmHg and 20oC) • Incident: Local standard was calibrated for dose to water, but incorrectly interpreted as dose in air • Consequence: – The error caused an overdose by 11% • Cause : Inadequate training, education Incorrect use of Calibration Certificate of the local standard dosimeter Assume a pressure P is as 630mmHg (1000m above sea level) & T as 20oC, then KTP= (273.2+20)* 760 / (273.2+20)* 630 = 1.206 IF pressure P is taken as 760mmHg (sea level) & T as 20oC KTP= (273.2+20)* 760/ ((273.2+20)* 760) = 1 The error in dose estimation will be about 20% lower, will result in excess dose to patient. Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 15 Slide 18 3

  4. 10-05-2023 Radiation Incidents resulting from insufficient understanding of planning system algorithm Case Study IV Error in calculation of Treatment Case Study V • Incident: – A 31-month old patient, being treated for a brain tumor, was to receive two Cobalt-60 teletherapy treatments of 150 rads each for a total dose of 300 rads to reduce swelling behind the patient's eye. – The dosimetrist mistakenly prepared the dose calculations for 300 rads per treatment. The patient was treated two days, with 300 rads per treatment for a total dose of 600 rads. • Incident: Wedge factor was applied twice • Sequence: – The Treatment planning system included the wedge correction in the dose distribution – The wedge factor was again included in the hand calculation of treatment time • Consequence: Overexposure up to 14% • Reasons: – Insufficient understanding of the treatment planning system algorithm Do not pay me twice Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 19 Slide 22 How could the wedge factor be included in the planning system? Error in calculation of Treatment Case Study V- Cause • The error was caused by the mistaken calculations by the dosimetrist • Inadequate review by the physician before the treatment began. • There was also a problem with the legibility and format of the treatment plan. 75 100 90 65 80 70 50 60 40 50 30 40 Normalized isodose Corrected isodose Wedge factor not included in isodose Wedge factor included in isodose Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 20 Slide 23 Error in calculation of Treatment Case Study v – Action taken How does it change the dose distribution? • The error was discovered by a student technologist during a monthly chart review • To prevent recurrence, the licensee has provided additional personnel to eliminate the types of problems that contributed to the misadministration. 100 120 115 60 158 60 80 80 training to treatment Wedge correction not included in the distribution Wedge correction included in the distribution Wedge factor should be included in Treatment time calculation Wedge factor should not be included in Treatment time calculation Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 21 Slide 24 4

  5. 10-05-2023 Use of Linear Accelerator in Physical Mode Case Study VII • Sequence – Linac was made to work on PHYSICAL mode by the electronics engineer on instruction from Radiation Oncologist – Output was measured with the help of Technologist in PHYSICAL mode – Instruction on how to operate in Physical mode was provided by the engineer and observed the first two treatments Accidents due to Machine Malfunction Case Study VI • Incident: – Loose wedge mounting and incorrect dose at the central axis • Cause: – Wedge mount was loose and hence for lateral beams the central axis wedge factors were incorrect and altered the dose distribution – Staff did not check the wedge mount and the wedge factor for horizontal beams Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 25 Slide 28 Use of Linear Accelerator in Physical Mode Case Study VII • Thirteen patients were treated with no problems and the last patient was on 10 MeV electrons • Next patient was set for treatment with 20MV x rays, dose rate 300MU/min, The treatment started but terminated after 21s and only a few monitor units were delivered • When the patient was removed from the room the radiographer noted skin reaction on the patient, which indicated a high degree of overexposure Off Centered wedge Excess attenuation { Lack of thickness { { } t t • Wedge factor depends on the thickness of the wedge ‘t’ at the central axis • Consequence: Patients received higher doses across the beam for horizontal machine position and low for opposite side horizontal treatment Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 26 Slide 29 Use of Linear Accelerator in Physical Mode Case Study VII • Incident: – Problem with selection of X-ray & Electron energies in the clinical mode – Linear accelerator was used in PHSYCAL mode for treatment. PHYSICAL mode is meant for servicing & research as most interlocks of linac are bypassed in this mode – Linac MAY NOT terminate the radiation if errors in Radiation output or if mechanical movements of target, foils or filters fail Use of Linear Accelerator in Physical Mode Case Study VII – contributing factors • On investigation it was found that there was extremely high dose at the center of the field caused by the failure to deploy, X-ray target, flattening filter and monitor chamber. • Cause: Operation in PHYSICAL mode disabled the interlocks that could have detected this dangerous condition Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 27 Slide 30 5

  6. 10-05-2023 Mishandling of equipment failure Case Study VIII Possible causes for Radiation Accidents in Brachytherapy • Improper calibration of Activity of the brachytherapy source • Improper identification of the source • Mishandling of the source • Incorrect input data to the planning system • Insufficient knowledge about the planning system algorithm • Mechanical failure or malfunction of brachytherapy equipment • Incident: The linac delivered 36MeV electrons regardless of the energy selected on the console • Sequence: – Linear accelerator failed to produce electron beams – Fault was attended by an maintenance technician – After the repair the analog display permanently displayed 36MeV regardless of energy selected Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 31 Slide 34 Mishandling of equipment failure Case Study VIII– Consequence Error in activity reporting Case Study I Error in units of reporting the activity for brachytherpay ribbons • Sequence: – The licensee ordered brachytherapy ribbons containing 0.79 millicurie per ribbon – However, the vendor delivered brachytherapy ribbons containing 0.79 milligrams radium equivalent (1.36 millicurie) per ribbon. – the prescription order was checked against what was received and noted that the quantities (0.79) matched, but failed to note that the amount received was measured in milligrams radium equivalent rather than the requested millicurie units • Incident: 27 patients were treated over a period of ten days till the physicians began to correlate poor tolerance and severe reactions observed in some patients with mall function of the machine Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 32 Slide 35 Error in activity reporting Case Study I –Consequence & Action taken • Consequence: The radiation dose to the patient's prostate gland was 5,669 rads (56.69Gy) rather than the prescribed 3,258 (32.58Gy) rads • Action Taken: – The referring physician was notified and chose not to inform the patient. The patient was examined during subsequent follow-up visits and has shown no adverse effects due to the increased radiation exposure. Mishandling of equipment failure Case Study VIII– contributing factor • Failure to select electron beam was due to a short circuit of the system that selects the trajectory of the electron beam • Ineffective communication – physicists were not notified immediately about the malfunction • Incorrect interpretation of conflicting signals; the analog meter showing 36MeV was ignored Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 33 Slide 36 6

  7. 10-05-2023 Incident with HDR after-loading unit. Case Study II- Cause Case Study I -Cause and lessons learnt • Reason for the Incident: – Failure verification of source strengths prior to implanting the brachytherapy sources. – Miscommunication between the licensee and the vendor also appears to have contributed to the error. • Lessons learnt: – To ensure that units of measurement received correspond to that was ordered source strengths should be verified by direct measurement prior to implantation. • • Cause: – Although a wall-mounted area monitor alarmed at various times when the source should have been retracted, the licensee's staff did not conduct a survey for radiation levels with the available portable radiation survey instrument. – The only action taken was to check the control console of the HDR remote afterloader which gave a false indication that the source was "safe“. of the staff to perform adequate Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 37 Slide 40 Incident with HDR after-loading unit. Case Study II- Incident with HDR after-loading unit. Case Study II- Cause Incident: A patient was treated for anal carcinoma with High Dose Rate (HDR) after loading Brachytherapy unit and the patient died on November 21, 1992. • HDR treatment with 4.3 Ci of Iridium-192 source was placed at various positions in each of the five catheters that were to remain in the patient for subsequent treatments. • The staff experienced placement in one of the patient's five treatment catheters. The Incident Investigation Team (IIT) reported that the event was caused by the following: 1. Weaknesses in their radiation safety program 2. Inadequate radiation safety training to the staff. 3. A number of weaknesses were found in the design and testing of the unit. – Weaknesses were identified in the testing and validation of source-wire design, and in the design of certain safety features of the HDR afterloader. difficulty with source Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 38 Slide 41 Incident with HDR after-loading unit. Case Study II- Sequence of events Incident with HDR after-loading unit. Case Study II- Cause • They were unaware that a short piece of the cable containing the Iridium source had broken off and remained in one of the catheters in the patient. The patient was transported to a nearby nursing home. The source remained in the patient's body for four days when the catheter fell out. • It was placed in a medical biohazard bag (red bag) in a storage room by nursing home personnel who did not know it contained the radioactive source • The safety culture contributed significantly to the event. – Technologists routinely ignored the PrimAlert-10 alarm. Its problems were worked around and not fixed. – Technologists did not afterloader, or the treatment room following HDR treatments. – The authorized user failed to wear a film badge on both occasions when the source was encountered; survey patients, the Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 39 Slide 42 7

  8. 10-05-2023 Incident with HDR after loading unit. Case Study II- Consequence Misadministration of the source Case Study III - Consequence The cause of death of the patient was reported as "Acute Radiation Exposure Thereof." Until the source was recovered after the patient's death, it subjected nursing home residents and staff, as well as visitors, to radiation exposure. Radiation doses to the 94 individuals associated with the event ranged from 40 mrem to 22 rem. • Numerous residents, employees, and visitors to the nursing home were unknowingly irradiated. • The oncologist had left verbal orders with the day shift charge nurse "not to change the dressing" but these orders were not passed on to the LPN.. • The patient's abdominal skin received an unnecessary exposure over various areas ranging from 172 rad to 1032 rad. The skin exposure to the hand of the LPN was 7.6 rad and Consequences Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 43 Slide 46 Misadministration of the source Case Study III Misadministration of the source Case Study III - Cause Incident: seeds were no longer implanted Sequence of events: – During a brachytherapy implant procedure, two ribbons, each containing six Ir-192 seeds, with a total activity of 48.25 mCi, were implanted into two catheters inserted into the patient's through an abdominal incision. A routine x-ray identified that the 1. Lack of oversight of the procedure by the licensee's Radiation Officer; and 2. Inadequate training of the nursing staff in that they were unable brachytherapy ribbon appropriately if, and when, they become dislodged. • Health and Safety to identify handle the and them common bile duct, Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 44 Slide 47 Misadministration of the source Case Study III – Action Taken & lessons learnt 1. Familiarization of personnel appearance of the radioactive brachytherapy treatments at the licensee's facility; 2. Naming a new RHSO who could devote sufficient time to the radiation safety program; 3. Developing a nurses' procedure manual; 4. Conducting formal in-service training in radiation safety with all nursing unit workers; and 5. Requiring a written directive be initiated before ordering radioactive material. Misadministration of the source Case Study III – sequence of events During the night shift, the patient's dressings on the wound were wet and loose. A licensed practical nurse (LPN), who responded to the patient, found the Ir-192 ribbons dislodged and lying loose on the patient's abdomen. The LPN, not realizing that it was radioactive, changed the patient's dressing and bed, and coiled each Ir-192 ribbon around her hand and taped them to the patient's abdomen. with the size used in and sources Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 45 Slide 48 8

  9. 10-05-2023 Summary – Potential accidents in External Beam Therapy Summary – Potential accidents in Brachytherapy • Possible errors in Calibration – Incorrect calibration of the teletherapy unit – Use of wrong decay chart for output of cobalt unit. – Not updating the output chart after source change – Lack of communication regarding units and depth of calibration. (e.g. Dmax or 5cm) • Improper calibration of the source activity • Improper identification of source • Inadequate routine QA for source integrity check • Inadequate source movement documentation • Incorrect use of treatment planning system • Insufficient understanding of the Algorithm of the planning system Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 49 Slide 52 Summary – Potential accidents in External Beam Therapy Summary – Potential accidents in Brachytherapy • Possible errors in Treatment Planning – Incorrect input data of Depth dose or Tissue maximum ratio – Multiple correction for use of wedge filter or compensators. – Miss application of distance correction. – Miss understanding the algorithm – Incorrect hand calculation and inadequate training and QA procedure • Inadequate routine QA procedure for Remote after loading unit • Improper and inadequate training of personal on radiation protection aspects • Insufficient documentation of policies and procedures for handling emergencies • Use of faulty zone monitors and survey meters Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 50 Slide 53 Summary – Potential accidents in External Beam Therapy References • ‘Lessons Learned from accidental exposures in Radiation Therapy’ – IAEA publication Safety Report Series No 17 • ‘Prevention of Accidental Exposures to Patients undergoing Radiation Therapy’ – Annals of the ICRP Publication No 86 • Basic Safety Standards – Safety series No 115 IAEA publication • Investigation of an accidental exposure of Radiotherapy patients in Panama – Report of a team of experts (IAEA publication 26 May-1June 2001) • Potential accidents due to machine malfunction – Improper accessory mounting – Use of Linear accelerator in Physical mode – Mishandling of the machine malfunction – Inadequate training for serving personnel – Improper documentation of polices and procedures for use & servicing of the machine – Inadequate routine QA procedures for teletherapy units Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Part VIII.5. Lecture 1 : Radiation Accidents and Lessons learnt Slide 51 Slide 54 9

More Related