Deformable image registration for cervical cancer brachytherapy dose accumulation: Organ at risk dose-volume histogram parameter reproducibility and anatomic position stability

PURPOSE: The purpose of this study was to determine the effect of deformable image registration (DIR) on cumulative organ at risk dose-volume histogram (DVH) parameter summation for more than three brachytherapy fractions. The reproducibility of different methods of DIR was tested. DIR was then used to assess the stability of the anatomic position of the DVH parameters within the bladder and rectum. METHODS AND MATERIALS: DIR was completed for 39 consecutive cervical cancer brachytherapy patients' planning CTs. Accumulated DVH parameters (D-2cc and D-0.1cc) for bladder and rectum were compared with dose summation without DIR. Reproducibility of DIR results was assessed for different methods of implementation based on adding contour biases added to the DIR algorithm. Vol(D2cc) and Vol(D0.1cc). ice structures were created from the overlap of the D-2cc and D-0.1cc isodose and the bladder or rectum, respectively. The overlap of Vol(D2cc) and VolD(0.1cc) structures was calculated using the Dice similarity coefficient. RESULTS: DIR accumulated D-2cc and D-0.1cc decreased by an average of 2.9% and 4.2% for bladder and 5.08% and 2.8% for rectum compared with no DIR. DIR was most reproducible when the bladder or rectum contour was masked. The average Dice similarity coefficient was 0.78 and 0.61 for the bladder D-2cc and D-0.1cc as well as 0.83 and 0.62 for rectal D-2cc and D-0.1cc, respectively. CONCLUSIONS: Dose decreases were observed for accumulated DVH parameters using DIR. Adding contour-based biases to the algorithm increases the reproducibility of D-2cc and Duce accumulation. The anatomic position of Vol(D2cc) was more stable than Vol(D0.1cc). Crown Copyright (C) 2017 Published by Elsevier Inc. on behalf of American Brachytherapy Society. All rights reserved.