Inter-application variation of dose and spatial location of D2cm3 volumes of OARs during MR image based cervix brachytherapy

Purpose: Evaluation of Inter-application variation of doses and spatial location of D-2cm3 volumes of OARs during MR-image based cervix brachytherapy. Materials and methods: Twenty-seven patients treated with EMBRACE protocol were analyzed. Every patient had two applications, one week apart. For each application patient had undergone MR-imaging (MR-1 and MR-2), volume delineation, reconstruction, treatment planning (plan-1 and plan-2) and dose evaluation. Both the image series were then co-registered with applicator as the reference coordinate system (Eclipse planning system v8.6.14). Inter-application dose, volume and spatial location of D-2cm3 variation were evaluated. Results: The largest inter-application systematic and random dose variations were observed for sigmoid as compared to rectum and bladder. The mean (+/- SD) of the relative D-2cm3 variations were 0.6(+/- 15.1)%, 0.9(+/- 13.1)% and 11.9(+/- 37.5)% for rectum, bladder and sigmoid respectively. The overlap of D-2cm3 volumes was more than 50% in 16(59%), 8(30%) and 3(11%) patients for rectum, bladder and sigmoid, respectively. Conclusion: The 2 cm(3) volumes between the applications/fractions are quite stable in topography for bladder and rectum, and hence the current practice of cumulative addition of D-2cm3 dose is expected to be valid for bladder and rectum. For sigmoid, significant topographical changes were seen, which need further validation in a larger patient population and in multi-centric settings. (C) 2013 Elsevier Ireland Ltd. All rights reserved.