Purpose: Interstitial brachytherapy implemented for locally advanced gynecologic cancer can result in toxicity due to the proximity of organs at risk (OAR). We report our experience using superflab bolus as vaginal packing to displace OAR during interstitial brachytherapy.
Material and methods: Twelve patients with stage IB-IVA gynecologic cancer were treated with definitive chemoradiation including interstitial brachytherapy. A Syed template was used for a computed tomography (CT)-based pre-plan with magnetic resonance imaging (MRI) fusion. A 1-2 cm superflab bolus was cut and sterilized. The tandem and obturator were placed, and superflab was then inserted into the vagina. Interstitial needles were then placed through the template and superflab as per the pre-plan under transabdominal ultrasound guidance. Prescription doses ranged from 85-90 Gy EQD2 including external beam radiation therapy (EBRT). 5-6 Gy per fraction was delivered biologically effective dose (BID) over 2-3 days in 1-2 implants. Toxicities were evaluated post-treatment, 1 month, and 3 months.
Results: The rectum, bladder, and sigmoid had significant average displacement from the prescription isodose line. The average reduction in D2cc between pre- and post-implant was 5.19 Gy per fraction (p < 0.0001), 7.19 Gy (p < 0.0004), and 1.78 Gy (p < 0.003) for the rectum, bladder, and sigmoid, respectively. The high-risk target volume (HR-TV) received a median D90 of 104% (range, 58-122%) of the prescription dose, and 92% (range, 71-131%) in the pre-/post-implant plans, respectively (p = 0.4).
Conclusions: Our initial experience with superflab as vaginal packing demonstrates technical feasibility and dosimetric improvement for OAR.
Keywords: brachytherapy; interstitial; intravaginal; radiotherapy; superflab.