Total skin electron therapy vertical profiles measured using radiochromic film

BACKGROUND: Vertical dose profiles of Total Skin Electron Therapy (TSET) electron fields are often measured using ionization chambers (ICs); however, resulting protocols are tedious and time consuming due to complex gantry arrangements, numerous point dose measurements and extra–cameral corrections. This inefficiency is reduced when using radiochromic film (RCF) dosimetry through simultaneous dose sampling and the elimination of IC‐related measurement corrections. PURPOSE: To investigate the feasibility of RCF dosimetry for TSET vertical profile measurements and establish a novel RCF based vertical profile quality assurance protocol. METHODS: Thirty‐one vertical profiles were measured using GAFChromic(®) EBT‐XD RCF on two matched linear accelerators (linacs) over 1.5 years. Absolute dose was quantified using a triple channel calibration method. Two IC profiles were collected for comparison to RCF profiles. Twenty‐one archived IC measured profiles from two different matched linacs from 2006 to 2011 were analyzed. Inter‐ and intra‐profile dose variability was compared between dosimeters. The time required for the RCF and IC protocols was compared. RESULTS: RCF measured inter‐profile variability ranged from 0.66%–5.16% and 1.30%–3.86% for the two linacs. A 0.2%–5.4% inter‐profile variability was observed for archived IC measured profiles. RCF measured intra‐profile variability ranged from 10.0%–15.8%; six of 31 profiles exceeded the EORTC ± 10% limit. Archived IC measured profiles exhibited lower intra‐profile variability (4.5%–10.4%). RCF and IC measured profiles agreed in the center of the field; however, RCF doses measured 170–179 cm above the TSET treatment box base were ∼7% greater. Modification to the RCF phantom eliminated this discrepancy, resulting in comparable intra‐profile variability and agreeance with the ±10% limit. Measurement times were reduced from 3 h (IC protocol) to 30 min (RCF protocol). CONCLUSIONS: RCF dosimetry improves protocol efficiency. RCF has been established as a valuable dosimeter for TSET vertical profile quantification when compared to ICs as the gold standard.