Radiochromic filmebased quality assurance for CT-based high-dose-rate brachytherapy Saeid Asgharizadeh 1,2 , Hamed Bekerat 1,2 , Alasdair Syme 1,2 , Saad Aldelaijan 1,2 , Franc ¸ois DeBlois 1,2 ,T e Vuong 2 , Michael Evans 1,3 , Jan Seuntjens 1 , Slobodan Devic 1,2, * 1 Medical Physics Unit, McGill University, Montr eal, Qu ebec, Canada 2 Department of Radiation Oncology, Jewish General Hospital, McGill University, Montr eal, Qu ebec, Canada 3 Department of Medical Physics, McGill University Health Centre, Montr eal, Qu ebec, Canada ABSTRACT PURPOSE: In the past, film dosimetry was developed into a powerful tool for external beam radiotherapy treatment verification and quality assurance. The objective of this work was the devel- opment and clinical testing of the EBT3 model GafChromic film based brachytherapy quality assur- ance (QA) system. METHODS AND MATERIALS: Retrospective dosimetry study was performed to test a patient- specific QA system for preoperative endorectal brachytherapy that uses a radiochromic film dosim- etry system. A dedicated phantom for brachytherapy applicator used for rectal cancer treatment was fabricated enabling us to compare calculated-to-measured dose distributions. Starting from the same criteria used for external beam intensity-modulated radiation therapy QA (3%, 3 mm), passing criteria for high- and low-dose gradient regions were subsequently determined. Finally, we inves- tigated the QA system’s sensitivity to controlled source positional errors on selected patient plans. RESULTS: In low-dose gradient regions, measured dose distributions with criteria of 3%, 3 mm barely passed the test, as they showed 95% passing pixels. However, in the high-dose gradient re- gion, a more stringent condition could be established. Both criteria of 2%, 3 mm and 3%, 2 mm with gamma function calculated using normalization to the same absolute dose value in both measured and calculated dose distributions, and matrix sizes rescaled to match each other showed more than 95% of pixels passing, on average, for 15 patient plans analyzed. CONCLUSIONS: Although the necessity of the patient-specific brachytherapy QA needs yet to be justified, we described a radiochromic film dosimetryebased QA system that can be a part of the brachytherapy commissioning process, as well as yearly QA program. Ó 2015 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved. Keywords: Radiochromic film dosimetry; Quality assurance; Brachytherapy Introduction Brachytherapy represents clinical use of small encapsu- lated radioactive sources at short distances from target vol- umes for irradiation of both malignant tumors and benign lesions. Brachytherapy methods vary considerably depend- ing on their complexity and the scope to which they are individualized to particular patients. The aim of a brachy- therapy quality assurance (QA) program should be to maxi- mize the likelihood that each treatment is administered accurately, recognizing the clinical intent and that it is per- formed safely for both the patient and others who might be exposed to radiation during the treatment. With the ad- vancements in brachytherapy treatment techniques, the need for comprehensive QA programs has been recognized (1), and the number of QA tools and procedures has been summarized in numerous recommendation documents (2e4). In addition, within the last decade, the brachyther- apy community witnessed a widespread use of various im- age guidance techniques and with it new challenges for brachytherapy QA programs (5, 6). The absence of patient-specific QA process in brachy- therapy is in contrast with the situation for intensity- modulated radiation therapy (IMRT) where this is a standard practice. External beamebased IMRT uses specialized computer-driven technology to create dose distributions that Received 25 November 2014; received in revised form 9 January 2015; accepted 8 February 2015. * Corresponding author. Medical Physics Unit, McGill University, Jewish General Hospital, 3755 Cote St-Catherine, Montreal, Qu ebec, Can- ada H3T 1E2. Tel.: þ1-514-340-8222/2595; fax: þ1-514-340-8642. E-mail address: slobodan.devic@mcgill.ca (S. Devic). 1538-4721/$ - see front matter Ó 2015 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.brachy.2015.02.192 Brachytherapy - (2015) -