Quality assurance in radiation therapy: physics efforts.

During the last two years, several important documents on quality assurance in radiation therapy have been published. In 1981 the Committee on Radiation Oncology Studies, in a report to the Director of the National Cancer Institute, outlined criteria for multidisciplinary cancer management, including technical standards in radiation therapy. In March 1983, a task group of the American Association of Physicists in Medicine (AAPM) submitted a document for review and publication on "The Physical Aspects of Quality Assurance in Radiation Therapy". This document addresses quality assurance problems related to: 1. treatment machines; 2. measurement equipment; 3. treatment planning; 4. treatment verification; 5. brachytherapy; and 6. radiation safety. One chapter in this latter document discusses the problem of estimating the uncertainty in dose delivered to a patient. The contributions to this uncertainty are analyzed and separated into dosimetric and spatial uncertainties. The dosimetric uncertainties resulting from the central axis calibration and treatment planning amount to about 5% at the 95% confidence level in an optimal situation. The spatial uncertainties resulting from machine alignment problems combined with patient set-up and organ motion may be about 8 mm to 10 mm, corresponding to two standard deviations. An example of how the spatial uncertainty translates into a dose uncertainty for a three-field esophageal plan is discussed.