Comparison of measured and calculated peripheral doses in patients undergoing radiation therapy.

Abstract

Many papers have been published on the measurement for specific treatment machines and/or techniques of the dose to points outside the primary beam, often called the peripheral dose (PD). Most papers concern measurements in phantoms. We report on the results of a comparison of estimates of the PD, based on these phantom measurements, with PDs measured on patients. A special holder with thermoluminescent dosimeters was placed against the perineum of patients referred to our institute for radiation therapy. The measured dose was then compared with the dose calculated on the basis of published PD data. For all measurements together, the calculated values exceeded the measured PDs by about 9%, with a standard deviation of 35%. The correlation varied between specific subgroups but the difference between measurement and calculation did not exceed 50%. We conclude that published PD data can be used to accurately predict the peripheral dose in the clinical situation.