The Risks of IMRT

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• The Risks of IMRT
• Reviewing the New York Incident

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The incidences happen

• The highly automated nature of IMRT decreases the
  risks
• The automatization does not eliminate them
• The best centers are not immune
• This section is based on the IAEA report

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In the State of New York

• The patient was booked to have an oropharynx IMRT
  treatment
• IMRT plan was prepared and the department done
  the standard checks
• Portal dosimetry to ensure correctness of the
• MLC positions
• Monitor units for each of the fields
• The treatment started and the first 4 fractions
  were delivered correctly

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The plan was reviewed by the doctor

• Was found to deliver excessive dose to the teeth
• Second plan was created
• Nothing unusual
• The plan was saved as new plan
• The system saves
• 1. The dose fluency maps
• 2. DRR
• 3. The MLC positions
• This was a normal procedure
• however the computer system crashed

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Next

• The dose fluency maps were saved
• The DRR were not completely saved
• MLC control data (position of MLCs) did not start
  as the system was expecting the completion of DRR
  saving process

Yes
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The application appeared frozen

• The DRR was locked into the failed first attempts
  to save
• Therefore the second attempt to save was not able
  to complete
• The user terminated the application manually
• The Database rolled back to the last known valid
  state
• 1. Actual fluency data
• 2. Partially saved DRRs
• 3. No MLC data

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The patient set was reopened on another work
station

• The isodoses were recalculated
• No need for MLC data for this

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No verification - pt proceeded to treatment
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The Consequences

• The patient was given 3 fractions
• Eventually it was noticed that the are no MLC
  shapes of screen
• Dose recalculated
• 3 fractions delivered 13Gy each
• The patient received 39Gy in 3 fractions

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Take home message

• We do relay on the machines even for basic
  assessment
• The QA steps are routine and boring
• One could not skip them, however
• Beware of crashing of the computer systems and
  restarting the process
• There is place for complacency
• Continuous assessment is job for everybody

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• This presentation is done with close co-operation
  with