VBT Yields Less Urethra Radiation Exposure in Endometrial Cancer vs EBRT in CRC

Patients with endometrial cancer who were treated with vaginal brachytherapy (VBT) experienced significantly less radiation exposure to the female urethra vs external beam radiation therapy (EBRT) for colorectal cancer (CRC), indicating that pelvic radiation therapy should be considered when counseling patients on urinary incontinence, according to results from a retrospective cohort study.

For patients in the VBT cohort, the mean volume dose was 1266 ± 533 cGy, leading to a urethral exposure of 42.2% of the total prescribed dose of 3000 cGy. In the EBRT cohort, the mean volume dose was 5051 ± 192 cGy, which lead to a urethral exposure of 101% of the total prescribed dose of 5040 cGy. The difference between arms was found to be statistically significant (P <.0001).

The study population was comprised of female patients with endometrial cancer and rectal cancer who were evaluated and treated at the Comprehensive Cancer Center, Wake Forest Baptist Health from 2014 to 2017. A convenience population of patients with stage I endometrial cancer treated with VBT was pulled from a previous prospective study. Patients in this group were treated with 3000 cGy of VBT delivered in 3 fractions to the top 50% of the vagina. The comparator arm of patients with rectal cancer who were treated with EBRT was identified via International Classification of Diseases–9/10 codes and Current Procedural Terminology codes. Those in this cohort received 4500 cGy in 25 fractions plus an additional 540 cGy in 3 fractions. CT imaging was performed in both cohorts before starting treatment.

A total of 32 women were identified, of whom 18 had endometrial cancer and received VBT, and 14 had rectal cancer and received EBRT. Five patients of 23 in the initial endometrial cancer population were excluded from the study due to lacking CT imaging (n = 2) and being prescribed a non-standard radiation regimen (n = 3). Additionally, 9 patients of 23 in the initial CRC population were excluded from the study, due to lacking available radiation dosimetry data (n = 7) and being prescribed a non-standard radiation regimen (n = 2).

The primary end point of the study was the highest radiation dose delivered to 0.2 cc of tissue within the contoured urethra or the volume dose. Secondary end points included the highest point doses delivered to the bladder neck and mid-urethra. Investigators also determined the mean radiation dose to the entire contoured urethral volume.

The mean patient age was 58.9 ± 8.1 years for those in the VBT cohort and 59.4 ± 13.8 years for the EBRT cohort. All patients in the VBT cohort had stage I tumors, while 79% of those in the EBRT group had stage III tumors and 21% had stage IV tumors. In terms of tumor histology, most patients receiving VBT had endometrioid adenocarcinoma (83.3%), and most patients in the EBRT cohort had adenocarcinoma (92.9%).

Overall, VBT was associated with less radiation exposure compared with EBRT across all secondary measures. In terms of bladder neck point doses of radiation, patients in the VBT cohort were exposed to 1559 cGy ± 499 vs 5085 cGy ± 162 in the EBRT cohort. Patients receiving VBT had a mid-urethra exposure of 1215 cGy ± 718 compared with 5057 cGy ± 185 in the EBRT group. The mean total urethral dose of radiation was 1096 cGy ± 495 for the VBT cohort vs 5024 cGy ± 205 for the EBRT cohort.

Reference

Hines K, Nieto K, Dezarn W, et al. An assessment of urethral radiation exposure in the treatment of endometrial and rectal cancers. Int Urogynecol J. Published online October 1, 2022. doi:10.1007/s00192-022-05363-7