Transvaginal Ultrasound-Guided Interstitial Brachytherapy For. Vaginal Tumors: A Fixed Template Technique

Lower vaginal tumors are difficult to manage with external beam radiotherapy (EBRT) because of vulvar morbidity. We report our experience with a fixed-template technique for transvaginal ultrasound (TVUS) guided transperineal interstitial brachytherapy (BT) for lower vaginal tumors. Seven patients with primary vaginal cancer (n = 4, T1-3N0) or recurrent endometrial cancer (n = 3) of the lower vagina were treated with EBRT (median dose 45 Gy) followed by interstitial BT. All patients underwent pre-treatment TVUS and magnetic resonance (MR) imaging with a vaginal obturator to simulate the TVUS probe. A custom template provided a radial array of potential needle positions at 8 mm spacing around a central hole for the TVUS probe. A stabilizer and stepper system designed for prostate brachytherapy determined the relationship between the probe and template . 18 G stainless steel needles were inserted transperineally under TVUS guidance. At the completion of the procedure, the template is detached from the stabilizer and sutured to the perineum. A CT scan was performed and the HRCTV and organs at risk were contoured on CT/MR images and a 3D plan was generated. A single implant was done for 6/7 patients, with 2 fractions of 6.5 Gy BID with a minimum 6 hour interval between fractions. One patient previously treated with EBRT received BT alone with 22 Gy in 4 fractions BID in 2 implants. Mean HRCTV volume was 22.3 cm3 and the median number of needles was 11. Mean D90% was 111% and mean V95% was 96.7%. The mean (range) V150% and V200% were 51.2% (31.1-75.8%) and 20.4% (7-49.2%), respectively. The mean EQD2(3Gy) D2cc of EBRT + BT for the bladder, urethra and rectum was 46 Gy, 46.1 Gy and 48.7 Gy. After a median follow-up of 30.1 months, 1 patient (T3 vaginal primary) had an out of field second primary of the vulva. MR and physical exam showed no evidence of tumor in the previously treated vagina. The most common acute toxicity was grade 1 vaginal discharge (4 patients). Only 1 case of ≥ grade 3 toxicity was seen (vaginal stenosis). In our experience, TVUS-guided transperineal interstitial BT using a fixed template technique is feasible. Our custom template allowed for precise placement under US guidance, good parallelism and spacing, and stability of the needles. We were able to identify the tumor on TVUS in the majority of the cases when compared to the HR-CTV done on MRI. We are moving forward with ultrasound-based intraoperative planning for these patients, delivering a single fraction per implant.