IMRT-Physics Aspects

S. Jack Wei, MD
University of Pennsylvania School of Medicine
Last Modified: October 22, 2003

Moderator: Theodore L. Phillips, MD., University of California, San Francisco

Lynn J. Verhey, PhD., University of California, San Francisco

  • IMRT is now commonly used for patient treatment.
  • Compared to 3D conformal treatment (3DCRT), IMRT requires increased commissioning time, increased treatment time, increased physics and dosimetry time, and patient-specific quality assurance (QA).
  • Due to the increased number of fields and small monitor units used per field, specific commissioning is required.
  • Specific commissioning and QA is needed for the multi-leaf collimators to verify leaf position, minimize leakage, etc.
  • The varying linear accelerators each have their own requirements (e.g. leaf design, interleaf field constraints, field size, etc.) depending on their manufacturer, and these each must be commissioned and verified.
  • Patient immobilization and target definition must be carefully performed.
  • Improved imaging during treatment is important for improving QA and the emerging technology of cone-beam CT has the potential to determine patient translation and rotation relative to a pre-treatment CT scan.
  • In conclusion, IMRT is increasingly becoming mature and requires vigilant and extensive QA
  • Improved imaging will allow better delivery of QA.


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