Realisation of radiographic film for IMRT QA at the Nepean Cancer Care centre

Abstract

The feasibility of using Kodak X-Omat V radiographic film as an absolute dosimeter for intensity modulated radiotherapy (IMRT) quality assurance (QA) at the Nepean Cancer Care centre was assessed. Several aspects of film dosimetry were addressed: film digitising, film processing and inherent film characteristics. The study included: the reproducibility, uniformity and geometric accuracy of a transmission film digitiser. The constancy for an automated film processor over a range of doses applicable to a single fraction IMRT step and shoot field, and film dose rate and fraction dependence. Equipment included: an AFGA Curix HT-330 processor, DoseLab for QA plan comparison, ePin, ISP EBT Gafchromic film, ImageJ, Kodak X-Omat V Ready Pack radiographic film, NE 2571 and 2581 ion chambers, Philips Pinnacle planning system, RW3 phantoms, Varian 21EX and 2100CD linear accelerators, Victoreen 07-424 and 07-443 single point densitometers, and a Vidar VXR-16 DosimetryPRO digitiser. Film processing resulted in an 11% error over a period of several months. For film digitising, a 5% optical density variation was measured between central and peripheral parts of the digitiser however this was corrected using DoseLab. Constancy of the light output was greater than 99% and magnification errors were less than 1 mm. Minimal dose rate and fraction dependence were observed for the film and minimal variations (<0.2%) between film manufacture batches were recorded