Sarcoma and Cutaneous Tumors

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MO_21_2658 - Permanent Interstitial Brachytherapy (PIB) using Cesium-131 in Vaginal Melanoma - A New Wide-Local Radiation Technique

Monday, October 22
10:45 AM - 12:15 PM
Location: Innovation Hub, Exhibit Hall 3

Permanent Interstitial Brachytherapy (PIB) using Cesium-131 in Vaginal Melanoma – A New Wide-Local Radiation Technique
S. Larkin1, C. Steber2, D. A. Cheek1, D. Pokhrel1, M. E. Randall1, and J. M. Feddock1; 1University of Kentucky Department of Radiation Medicine, Lexington, KY, 2Emory University Department of Internal Medicine, Atlanta, GA

Purpose/Objective(s): Vaginal melanoma is a rare and aggressive malignancy, and most women present with locally advanced disease at the time of diagnosis. Surgical resection involving wide local excision (WLE) or pelvic exenteration remains standard of care, though morbidity is high and local control is poor. We present a novel radiation technique using Cesium-131 permanent interstitial brachytherapy (PIB) in place of surgical resection, followed by hypo-fractionated external beam radiation (RT).

Materials/Methods: Five patients with biopsy-proven primary vaginal melanoma were treated at our institution between June 2012 and December 2016. Treatment to gross disease consisted of an upfront high dose PIB using Cesium-131, most commonly delivering 50 Gy to 5mm depth. This was followed 2-3 weeks later with hypo-fractionated external radiation therapy (RT) to local and regional lymphatics using 30 Gy in 10 fractions, or equivalent. Systemic therapy using cytotoxic or biologic chemotherapy was not utilized. Patients were assessed for local, regional, and distant failures. Toxicities were scored according to Radiation Therapy Oncology Group (RTOG) toxicity criteria.

Results: The median age for all patients was 66 (range 56-93). All patients had International Federation of Gynecologic Oncology (FIGO) Stage II-III disease, 3 with multifocal vaginal disease, and 2 patients had clinically positive inguinal lymph nodes. Each site of gross disease was implanted using 131Cs, and to a median area of 4 cm3 (range 1-12 cm3). The prescription dose for all PIB implants was 50 Gy to 5mm except in one patient, where due to large size, the prescription dose was reduced to 35 Gy to 5mm. Adjuvant pelvic RT was added to achieve a high equivalent dose at 2Gy per fraction (EQD2) of median 92.2 Gy (range 92.2Gy – 107.9 Gy) and Biological effective dose (BED) of 76.8 Gy (range 76.8 – 89.9 Gy). A clinical complete response prior to the completion of external RT was identified in all patients. After a median follow-up time of 19.1 months (range 4.7 – 52 mos), only one patient has been found to have persistent local disease, that was successfully salvaged with an additional PIB procedure. All remaining patients remained locoregionally controlled. Two women developed pulmonary metastases at 3.1 and 8.1 months, which eventually lead to their deaths. One woman died of other causes with no evidence of disease after 52 months. No grade 2 or higher toxicities have been identified attributable to PIB.

Conclusion: Permanent interstitial brachytherapy using Cesium-131 combined with hypo-fractionated external RT is an effective initial treatment strategy for addressing gross disease in patients with vaginal melanoma. It has a favorable toxicity profile, appears to provide excellent local-regional control, and may have the ability to replace surgical resection.

Author Disclosure: S. Larkin: None. D.A. Cheek: None. M.E. Randall: Co-Chair, Uterine Corpus Committee; Gynecologic Oncology Group. J.M. Feddock: Consultant; Radiadyne. Paid Educational Speaker; Isoray.

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