Portal dose images I: Quantitative treatment plan verification

John W. Wong, Eric D. Slessinger, Russell E. Hermes, Carolyn J. Offutt, Tapan Roy, Michael W. Vannier

Research output: Contribution to journalArticlepeer-review


The comparison of a predicted portal dose image, calculated during treatment planning, with the measured image obtained during treatment is proposed as an approach to verify the correct implementation of a patient treatment plan. The comparison inherently verifies both the geometric alignment and the dose delivered. Feasibility studies were conducted with 60Co irradiation of a modular plastic phantom, an anthropomorphic phantom and a patient with lung cancer. Calculations were made with the 3-dimensional scatter ray-trace Delta Volume method. Calculated distributions and/or selected points of transmitted dose correction factors were compared with measurements made with TLD, scanning ionization chamber and film. For the two phantom studies, excellent agreement, usually to within 3%, was achieved when positioning of the phantoms were accurate. The patient study showed that selected point comparisons were inadequate in identifying the cause of errors when disagreement occurred. Simple subtraction of the calculated and measured images showed a 4 mm translational misalignment. The results are encouraging and demonstrate that portal dose images can be used to detect large geometric and dosimetric discrepancies between treatment plan calculations and measurements. The results also show that perfect verification is virtually impossible in the clinical situation. More work is required to use the verification information for improving the estimation of dose to the patient.

Original languageEnglish (US)
Pages (from-to)1455-1463
Number of pages9
JournalInternational journal of radiation oncology, biology, physics
Issue number6
StatePublished - Jun 1990
Externally publishedYes


  • 3-dimensional dose calculations
  • Portal image
  • Treatment verification

ASJC Scopus subject areas

  • Radiation
  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Cancer Research


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