Optically stimulated luminescence dosimeters as an alternative to radiographic film for performing “Head-Wrap” linac leakage measurements

Abstract

The linac “head-wrap”, where a new or modified linac is covered with radiographic film as a means to identify regions of increased radiation leakage, is an important part of the linac acceptance/commissioning process. However, as radiographic film and developing equipment decrease in availability and increase in cost, a simple, reusable, non-chemical solution becomes increasingly desirable. This study investigated whether discrete dose points measured using optically stimulated luminescence dosimeters (OSLDs) could be used to detect regions of increased radiation, as a substitute for radiographic film. After establishing the ability of the OSLDs to detect leakage and differentiate between high and low leakage doses, via a set of proof-of-concept measurements made in known high and low leakage regions on a Varian iX linac, a systematic evaluation of leakage at the surface of the linac head was undertaken. 60 OSLDs were positioned at regular intervals over the linac head by a member of the research team who was unfamiliar with the expected patterns of linac leakage. The OSLD measurements were able to detect linac head leakage and quantify high and low doses (from 0.6 to 44.7, cGy per 10,000 MU) with sufficient geometric precision to guide the use of an ionisation chamber to measure leakage doses in the patient plane. Reusable point dosimeters such as OSLDs are a promising solution to the problem of diminishing availability of film stock for linac head-wrap tests.