Deformable image registration for cervical cancer brachytherapy dose accumulation: Organ at risk dose-volume...

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.

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 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 Vol_D0.1cc structures was calculated using the Dice similarity coefficient.

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.

Dose decreases were observed for accumulated DVH parameters using DIR. Adding contour-based biases to the algorithm increases the reproducibility of D_2cc and D_0.1cc accumulation. The anatomic position of Vol_D2cc was more stable than Vol_D0.1cc.