Dose accumulation during vaginal cuff brachytherapy based on rigid/deformable registration vs. single plan addition.

PURPOSE: To compare dose summation using a single plan (SP) approach for vaginal cuff brachytherapy (VBT) against dose summation after a rigid or deformable registration for each VBT fraction, in women with early stage endometrial cancer receiving postoperative VBT.

METHODS AND MATERIALS: A retrospective analysis of 19 patients who received VBT as the sole adjuvant treatment was undertaken. For the purposes of the study, every VBT fraction was re-segmented and re-planned under the same conditions. CT-planning images were registered, initially following a rigid method and then using deformable registration. The transformation vectors were reused to warp the dose files, followed by the dose summation. Three dose accumulation scenarios were studied: (1) an SP approach, (2) a rigid dose warping summation (RDWS), (3) a deformable dose warping summation (DDWS). Each scenario was analyzed for 3 and 5 fractions to evaluate the effect of fractionation. D0.1cc, D1cc, D2cc, D5cc, D5%, and Dmean values were compared for organs at risk, such as the rectum and bladder.

RESULTS

No statistical significances were observed in rectal parameters between SP and RDWS or between SP and DDWS. Significant SP, RDWS and DDWS Dmean, D0.1cc, and D2cc metric differences for the 5 fractions bladder scenario were observed (p = 0.0242, 0.0196, and 0.0242, respectively).

CONCLUSIONS

A multi-image planning procedure for a VBT course leads to limited differences between different summation methods. SP is an effective and acceptable surrogate for absorbed doses in organs at risk.