PO26

Purpose Radiation toxicity to female erectile tissue, specifically the bulboclitoral apparatus, has not been previously investigated. This retrospective cohort study aims to demonstrate the feasibility of contouring the bulboclitoris (BC) and evaluate dose received by the BC in patients who underwent interstitial gynecologic brachytherapy for tumors involving the lower vagina and periurethral region. Materials and Methods Patients were treated with HDR brachytherapy between the years 2017 and 2022. All patients underwent IMRT external beam radiotherapy (EBRT) to the pelvis and bilateral inguinal region (45 Gy in 25 fractions) followed by High Dose Rate Ir-192 interstitial brachytherapy using the CT/MR M.A.C. Interstitial Gyn Template in 5 fractions for a total dose of 25 Gy (range, 22.5 - 27.5 Gy). The bulboclitoris (BC) was contoured retrospectively by a radiation oncologist and a pelvic radiologist using T2 MRI sequences fused to the pre-treatment and brachytherapy CT simulation. Superiorly, the BC was defined as inferior to the pubic symphysis and attached to the suspensory ligament of the clitoris. Laterally, the crura extend on either side of the corpus. Inferiorly, the vestibular bulbs flank the urethra and vagina on either side and do not extend posteriorly beyond the vagina. A representative contour of the bulboclitoral apparatus is depicted in Figure 1. Dosimetric data for the BC were calculated using EQD2 assuming an alpha-beta ratio of 3 Gy. Median follow up, local control, and vaginal morbidity using CTCAE version 4.0 for vaginal stenosis and pain scoring of the BC was evaluated. Results Patients had a median age of 65 years (range, 49-73). Three of the five patients had a diagnosis of squamous cell carcinoma of the vagina, one patient had recurrent cervical cancer in the vagina, and one patient had endometrioid adenocarcinoma involving the vagina. All tumors were located in the lower vagina, near the BC and urethra. The high-risk clinical target volume (HR-CTV), bladder, rectum, and urethra were contoured on patient imaging during initial treatment planning. Mean D90 of the HR-CTV was 79.82 Gy (range, 72.2-89.9 Gy), mean D2cc to the bladder was 66.54 Gy (range, 50.0-87.2 Gy), mean D2cc to the rectum was 60.9 Gy (range, 46.9-72.9), and mean D0.1cc to the urethra was 79.28 Gy (range, 53.9-93 Gy). At a median follow up of 19.6 months, all patients had a complete local response. One patient had systemic progression and died of metastatic disease. The mean pre-treatment volume of the bulboclitoris was 16.6 cc (range, 11.9 - 20.9 cc) and at brachytherapy was 12.66 cc (range, 7.3 - 22.1 cc). The mean IMRT dose to the BC was 45.87 Gy (range, 44.79 - 46.66 Gy) and mean HDR dose was 14.02 Gy (range, 11.23 - 18.88 Gy). Assuming an alpha-beta ratio of 3 Gy, mean bulboclitoral D90 EQD2 was 62.93 Gy (range of 58.72 to 67.22 Gy). In the acute period, all patients reported severe pain in the clitoral glans region and dysuria that completely resolved after 2 years. Grade 1-2 vaginal stenosis occurred in all patients despite vaginal dilator usage. One patient reported decreased clitoral sensitivity and inability to achieve clitoral-mediated orgasm 5 months after radiotherapy. Conclusions This study demonstrates that contouring the bulboclitoris is feasible and that the BC receives a significant radiation dose during gynecologic brachytherapy which can cause clitoral pain and dysfunction. Further studies are needed to evaluate the dose response of the bulboclitoris as well as explore methods to spare the organ during radiation therapy in order to minimize toxicity and preserve sexual function. Radiation toxicity to female erectile tissue, specifically the bulboclitoral apparatus, has not been previously investigated. This retrospective cohort study aims to demonstrate the feasibility of contouring the bulboclitoris (BC) and evaluate dose received by the BC in patients who underwent interstitial gynecologic brachytherapy for tumors involving the lower vagina and periurethral region. Patients were treated with HDR brachytherapy between the years 2017 and 2022. All patients underwent IMRT external beam radiotherapy (EBRT) to the pelvis and bilateral inguinal region (45 Gy in 25 fractions) followed by High Dose Rate Ir-192 interstitial brachytherapy using the CT/MR M.A.C. Interstitial Gyn Template in 5 fractions for a total dose of 25 Gy (range, 22.5 - 27.5 Gy). The bulboclitoris (BC) was contoured retrospectively by a radiation oncologist and a pelvic radiologist using T2 MRI sequences fused to the pre-treatment and brachytherapy CT simulation. Superiorly, the BC was defined as inferior to the pubic symphysis and attached to the suspensory ligament of the clitoris. Laterally, the crura extend on either side of the corpus. Inferiorly, the vestibular bulbs flank the urethra and vagina on either side and do not extend posteriorly beyond the vagina. A representative contour of the bulboclitoral apparatus is depicted in Figure 1. Dosimetric data for the BC were calculated using EQD2 assuming an alpha-beta ratio of 3 Gy. Median follow up, local control, and vaginal morbidity using CTCAE version 4.0 for vaginal stenosis and pain scoring of the BC was evaluated. Patients had a median age of 65 years (range, 49-73). Three of the five patients had a diagnosis of squamous cell carcinoma of the vagina, one patient had recurrent cervical cancer in the vagina, and one patient had endometrioid adenocarcinoma involving the vagina. All tumors were located in the lower vagina, near the BC and urethra. The high-risk clinical target volume (HR-CTV), bladder, rectum, and urethra were contoured on patient imaging during initial treatment planning. Mean D90 of the HR-CTV was 79.82 Gy (range, 72.2-89.9 Gy), mean D2cc to the bladder was 66.54 Gy (range, 50.0-87.2 Gy), mean D2cc to the rectum was 60.9 Gy (range, 46.9-72.9), and mean D0.1cc to the urethra was 79.28 Gy (range, 53.9-93 Gy). At a median follow up of 19.6 months, all patients had a complete local response. One patient had systemic progression and died of metastatic disease. The mean pre-treatment volume of the bulboclitoris was 16.6 cc (range, 11.9 - 20.9 cc) and at brachytherapy was 12.66 cc (range, 7.3 - 22.1 cc). The mean IMRT dose to the BC was 45.87 Gy (range, 44.79 - 46.66 Gy) and mean HDR dose was 14.02 Gy (range, 11.23 - 18.88 Gy). Assuming an alpha-beta ratio of 3 Gy, mean bulboclitoral D90 EQD2 was 62.93 Gy (range of 58.72 to 67.22 Gy). In the acute period, all patients reported severe pain in the clitoral glans region and dysuria that completely resolved after 2 years. Grade 1-2 vaginal stenosis occurred in all patients despite vaginal dilator usage. One patient reported decreased clitoral sensitivity and inability to achieve clitoral-mediated orgasm 5 months after radiotherapy. This study demonstrates that contouring the bulboclitoris is feasible and that the BC receives a significant radiation dose during gynecologic brachytherapy which can cause clitoral pain and dysfunction. Further studies are needed to evaluate the dose response of the bulboclitoris as well as explore methods to spare the organ during radiation therapy in order to minimize toxicity and preserve sexual function.