2897 - Vaginal Cylinder Brachytherapy: An Analysis of Dose/Fractionation Regimens on Vaginal Stenosis and Endometrial Cancer Local Recurrence

Purpose/Objective(s): Radiation therapy is an important component of the management of gynecologic cancers. Vaginal brachytherapy (VBT) involves the use of a radioactive source placed into a cylinder applicator which is subsequently placed to treat the vaginal cuff. Currently, there are two primary dose/fractionation regimens of VBT used nationally, one of 3 fractions and another of 5 fractions. These two regimens have significantly different biologically equivalent doses. To date, there are few studies comparing results in a similar patient population at a single institution. We evaluated the effect of dose/fractionation on general toxicity, stenosis, and recurrence.

Materials/Methods: This is a single institution retrospective review of patients with Stage I-III endometrial cancer who received adjuvant VBT between January 19, 2012 through February 1, 2024. High dose rate (HDR) VBT was delivered via a vaginal cylinder prescribed to a depth of 5mm, to a dose of 21 Gy in 3 fractions or 30 Gy in 5 fractions prescribed to the surface. The total EQD2(a/b = 10) for each regimen was calculated to the surface as 57.75 Gy for the three-fraction regiment and 40 Gy for the five-fraction regimen. Those who did not receive VBT as part of initial treatment or who also received EBRT were excluded. Outcome measures include degree of vaginal stenosis, cancer recurrence and GI/GU toxicity. Unpaired t-tests were used for statistical analysis of continuous variables.

Results: A total of 163 patients were identified that met criteria with 100 patients treated with 21 Gy regimen and 63 patients treated with 30 Gy regimen with a median follow up of 38 months and 24 months respectively. Total incidence for vaginal stenosis of any degree was 29% for 21 Gy regimen compared to 33% for 30 Gy regimen with a p-value of 0.56. Specifically, for moderate and severe vaginal stenosis, an incidence of 8% for 21 Gy regimen compared to 0% for 30 Gy regimen was found with a p-value of 0.02. For GI and GU side effects, an incidence of 10% and 12% was found for 21 Gy regimen compared to 8% and 6% for 30 Gy regimen with a p-value of 0.66 and 0.24 respectively. For local cancer recurrence, a 2% incidence was found in 21 Gy regimen versus 6% in 30 Gy regimen with a p-value of 0.15.

Conclusion: More moderate to severe vaginal stenosis was found in patients in the 21 Gy regimen versus the 30 Gy regimen (8% versus 0%, respectively.) In terms of local cancer recurrence, the 21 Gy regimen was found to trend towards less incidence (2%) relative to the 30 Gy regimen (6%). Given the increased biological dose of the three-fraction regimen, these results confirm potential increased vaginal toxicity with a trend toward better control. No significant differences for GI or GU toxicities. Further research would be appropriate to include more patients to increase the power of the study and to identify if there is a meaningful difference in local recurrence.