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.