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Radiochromic Film Based System for CTDI Measurements

N Tomic

N Tomic1*, N Sharoubim2, F DeBlois3, J Seuntjens4, S Devic5, (1) McGill University, Montreal, QC, (2) McGill Unversity, Montreal, Quebec, (3) McGill University, Montreal, Quebec, (4) McGill University, Montreal, QC, (5) McGill University, Montreal, QC

SU-D-103-5 Sunday 2:05PM - 3:00PM Room: 103

Purpose: We demonstrate a new method for computed tomography dose index (CTDI) measurements performed on CT scanners using XR-QA model radiochromic film dosimetry system. Method was tested by comparing measured to CT scanner listed CTDI values for fifteen different CT scanners at various locations.

Methods:Reference dosimetry system was calibrated in terms of air kerma in air. Dose profiles were measured with XR-QA2 radiochromic film strips, sandwiched between acrylic rods cut in half and placed within CTDI phantoms. Film strips were scanned before and after irradiation with Epson Perfection V500 scanner in reflective mode. Reflectance change was measured using red color channel from TIFF images of scanned films and it was converted into air kerma in air using calibration curves. Measured air kerma in air was subsequently converted into absorbed dose to water following AAPM TG-61 protocol. We also investigated the impact of scan length by scanning CTDI phantom 5, 10, and 15 cm longitudinally.

Results:Average doses along profiles from each film piece were used to calculate weighted CTDIvol. Average difference for the first 10 scanners between calculated and listed CTDIvol was 21.8% for Head and 10.4% for Body protocol. Our study also showed that as the scanning length was increasing, the difference between measured and tabulated CTDIvol decreased. For the last 5 CT scanners, the scanning length of 5-10 cm was changed to 15 cm for both Head and Body scanning protocols, resulting in average difference between measured and tabulated CTDIvol values of 3.8% for Head and 9.4% for Body scanning protocol.

Conclusion:In contrast to ionization chamber measurement, the proposed method requires only a single exposure, does not need stem effect correction, and provides an acceptable accuracy when compared to CT scanner listed CTDIvol values. It also measures dose profiles allowing measurements of DLP and peak doses.

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