Single Or Multichannel Vaginal Cuff Hdr Brachytherapy - Is Replanning Necessary Prior To Each Fraction?

Adjuvant High Dose Rate (HDR) Vaginal Brachytherapy (VB) is commonly utilized for endometrial cancer. The value of customized treatment plans for every fraction for VB has been questioned. To date, studies have shown little benefit of replanning specifically for single channel VB. Multi-channel cylinders are also used in this setting, which may provide more conformal dosimetry and better compensate for single line source anisotropy at the vaginal apex. We evaluated the dosimetric and cost differences of using either a single plan or replan prior to each fraction for both single channel as well as multi-channel VB. We evaluated 25 patients that were treated with HDR VB at our institution. Sixteen patients were treated with single channel HDR VB by one physician, and 9 were treated with multi-channel HDR VB by a second physician. All single channel VB patients received a total of 3 fractions, and multi-channel VB patients a total of 4 fractions, each of which was preceded by a CT simulation scan and for which a unique treatment plan was generated. All dose points were defined based on ICRU 38. For this study, we calculated the dose to critical organs based on a decay-and-treat method utilizing the original catheter dwell-times for the initial fraction. These critical organ doses were then statistically compared with the original calculated doses for each patient based on fractional re-planning with paired, two-tailed Student's t-tests. Additionally, the data for costs of the various treatments at our institution were determined. For all patients treated with single channel VB, the mean dose difference was 6.5 cGy for bladder and 4.8 cGy for rectum between the replan and decay methods when calculated using the average dose for each patient across all fractions. The maximum dose difference was 56 cGy for bladder and 49 cGy for rectum. For multi-channel VB, the mean dose difference was 1.3 cGy for bladder and 10 cGy for rectum, and the maximum dose difference was 43 cGy for bladder and 46 cGy for rectum. The bladder and rectum doses were not significantly different between the replan and the decay method for either single channel (p=0.08 for bladder, p=0.18 for rectum) or multi-channel (p=0.85 for bladder, p=0.10 for rectum) VB. At our institution, the average additional hospital and professional costs per patient from repeat CT simulation and replanning is $8,498 for single channel and $12,747 for multi-channel VB. Our data shows no dosimetric advantage of replanning prior to each fraction for either single or multi-channel post-operative VB. Thus, we conclude that fractional replanning should not be utilized on a routine basis especially in light of the much higher costs associated with it. These results support the recent American Brachytherapy Society consensus guidelines for vaginal cuff brachytherapy.