Relative profile and dose verification of intensity-modulated radiation therapy. Academic Article uri icon

Overview

abstract

  • PURPOSE: To develop a quality assurance (QA) procedure to assess the intensity profile and dosimetry for intensity-modulated (IM) treatment fields using electronic portal imaging devices (EPIDs). METHODS AND MATERIALS: A series of rapidly acquired (approximately 1/sec) portal images are summed and converted to dose. For relative intensity QA, the intended profile is subtracted point-by-point from the measured profile forming a series of error values. The standard deviation, sigma, of the errors, a measure of the goodness of the match, is minimized by applying a normalization and uniform scatter subtraction from the measured profile. For dose verification (dose to isocenter), an empirically determined phantom-correction factor is added to incorporate the effect of patient presence on EPID readings. Seventy prostate treatment fields were used in a phantom study to verify these approaches. Sensitivity was studied by creating artificial mismatches. RESULTS: The average sigma for relative profile verification is 3.3% (percentage of average intended intensity) whereas artificial mismatches resulted in sigma values from 5% to 27%. The average isocentric dose calculated from EPID readings is 1.001 relative to the planned dose with a standard deviation of 0.018. CONCLUSIONS: An EPID can be used for profile verification and absolute isocentric dose measurement for IM fields.

publication date

  • April 1, 2000

Research

keywords

  • Quality Control
  • Radiotherapy Dosage
  • Radiotherapy, Computer-Assisted

Identity

Scopus Document Identifier

  • 0034176959

Digital Object Identifier (DOI)

  • 10.1016/s0360-3016(99)00555-6

PubMed ID

  • 10758329

Additional Document Info

volume

  • 47

issue

  • 1