Modified Houdek vault applicator for high-dose-rate brachytherapy: a technical report and case series

Introduction
Treatment of isolated post-surgical vault recurrence of cervical and endometrial cancers in previously unirradiated patients includes external beam radiotherapy (EBRT) ± concomitant chemotherapy, followed by brachytherapy (BT) boost. Supra-vaginal component of vault disease often requires interstitial BT for optimal dose coverage. We describe technical details and preliminary case series using modified Houdek vault applicator (MHVA) developed at our institution for limited intra-cavitary plus interstitial high-dose-rate (HDR) vault BT.

Material and methods
Nineteen patients with vaginal vault recurrences received BT boost with MHVA between October 2015 and May 2018. All underwent BT application and CT-based BT planning after completion of EBRT ± concomitant chemotherapy.

Results
Median EQD2 of BT dose in patients with carcinoma cervix recurrence (n = 15, / = 10) was 18.8 Gy, and in those with endometrial cancer recurrence was 22.08 Gy (n = 4, / = 4.5). Median total EQD2 was 68.8 Gy and 72.08 Gy, respectively. Mean 2 cc of bladder, rectum, and sigmoid EBRT + BT doses (EQD2, / = 3) were 65.38 Gy (±7.76), 63.37 Gy (±5.52), and 57.04 Gy (±4.45), respectively. At 6-8 weeks, 17 patients showed complete response (CR). With median follow-up of 20.5 months, 2-year overall survival was 95% (95% CI: 85.2-100.0%), and 2-year progression-free survival was 79.4% (95% CI: 61.0-97.8%). Late toxicities seen were grade 2 proctitis in 1 patient, grade 1 proctitis in 5, grade 2 urethritis in 1, grade 3 cystitis in 1, and recto-vaginal fistula in 1 patient (with disease controlled). Recurrence rate was 6.7 times higher in patients with post-EBRT disease greater than 10 mm (p = 0.01).

Conclusions
MHVA is a simple solution for intra-cavitary and interstitial HDR-BT boost in isolated vault cancers post-surgery, achieving acceptable dosimetric parameters. Preliminary clinical outcomes and late toxicities are satisfactory.