Individual fraction optimization vs. first fraction optimization for multichannel applicator vaginal cuff high-dose-rate brachytherapy

Purpose: To challenge the assumption of unchanged interfractional geometry changes in the course of fractionated multichannel vaginal cuff high-dose-rate brachytherapy. Methods and materials: Two methods of treatment planning for delivery of vaginal cuff brachytherapy were compared in 44 applications. Individual fraction optimization (IFO)-performed for the specific geometry of each individual fraction-was compared to first fraction optimization (FFO)-an optimized first fraction, applied unaltered for geometry of subsequent fractions in the same patient. Dose difference to critical organs was expressed as the percentage of the prescribed dose. Results: In the paired analysis for IFO vs. FFO, mean and maximum rectal and bladder doses were similar. However for FFO, an excess of greater than 20% mean dose to either bladder or rectum was observed in 41% of cases. Maximum organ doses were exceeded by 20% in 54.5% of applications. Conclusions: On the basis of these findings, it can be concluded that IFO may be important to minimize doses to critical structures.