Faculty Bibliography

Purpose: This study evaluates the dosimetry of conformal boost to persistent gross recurrent disease in the vagina with a balloon based, multi-channel (MC) CapriTM vaginal brachytherapy applicator in patients with recurrent gynecologic cancer at the vagina following whole pelvis radiation. Materials and Methods: All patients had fiducial markers placed at the site of gross disease, and were treated with whole pelvis radiation to a dose of 45 Gy in 25 fractions. Following whole pelvis radiation, patients were treated with Ir-192 HDRvaginal brachytherapy. Patients underwent sizing using the balloon-based, MC CapriTM applicator (Varian Medical Systems, Palo Alto, CA, USA) expanded to maximum capacity with saline to a median volume of 69 cm3 (range, 45-81 cm3) in order to secure applicator position. A computed tomography CT scan was performed with applicator in place. Target volume was defined as the gross tumor volume delineated by fiducial markers and expanded by 3 mm to create the planning target volume (PTV). Using Brachytherapy Planning in the Eclipse treatment planning system (Varian, Palo Alto, CA, USA), dosimetry of the conformal boost plan was manually optimized to achieve 100% coverage of PTV coverage using a prescription of 4 Gy per fraction using the minimum number of catheters and dwell positions closest to the target volume. Maximum dose to 2 cm³ (D2cm³) to bladder and rectum, as well as vaginal mucosal surface points ipsilateral and contralateral to PTV 400 cGy and biologically equivalent dose in 2Gy equivalents (EQD2) for bladder and rectum were calculated using a prescription of 4Gy x 6 fractions with alpha/beta of 3. Results: Five plans were evaluated from 5 patients with vaginal cancer (2) and endometrial cancer (3) with vaginal cuff recurrences. PTV average dimensions, calculated from the vaginal surface, were 1.13 cm depth, 2.60 cm width and 2.37 cm height. The median number of loaded catheters used in each optimized plan was 3 (range, 2-4 catheters). The average GTV measured 1.3 cm³ (range, 1.0-1.8 cm³), and the PTV measured an average volume of 4.8 cm³ (range, 3.2-6.4 cm³). D99 to PTV for all 5 plans was 100%, average maximum dose to ipsilateral vaginal mucosa was 13.0 Gy (range, 11.8-14.2 Gy), average maximum dose to the contralateral vaginal mucosa was 2.6 Gy (range, 2-3.4 Gy), average D2cm³ to bladder was 3.2 Gy (range, 2.1-4.2 Gy), and average D2cm³ to rectum was 3.7 Gy (range, 3.1-4.8 Gy). Average EQD2 total for 45 Gy external beam and 6 fractions of 4Gy was 67.7 Gy for the bladder (range, 56.0-79.5 Gy) and 74.3 Gy for the rectum (range 67.6-88.1 Gy). Conclusions: Although ABS Consensus Guidelines for vaginal cancer suggest that lesions with a thickness exceeding 5 mm cannot be adequately treated with a vaginal cylinder, we demonstrate that with the Multichannel Balloon CapriTM applicator, PTV depths averaging 1cm from vaginal surface were able to prescribed using a multicatheter approach with clinically acceptable bladder, rectal and vaginal doses. Preliminary data suggests that the use of the Multicatheter CapriTM applicator may be an alternative approach to using an interstitial implant for selected patients with small vaginal recurrences, however, a larger cohort of patients with long-term follow-up is required to assess longterm clinical outcomes using this technical approach. Figure 1. PTV shown with fiducial markers located on right lateral vaginal wall for patient treated with CapriTM multichannel vaginal applicator demonstrating isodose lines of 12 Gy, 4 Gy and 2.5 Gy. (Figure Presented)

INTRODUCTION: Evaluate use of novel multi-channel applicator (MC) Capri to improve vaginal disease coverage achievable by single-channel applicator (SC) and comparable to Syed plan simulation. MATERIALS AND METHODS: Twenty-eight plans were evaluated from four patients with primary or recurrent gynecologic cancer in the vagina. Each received whole pelvis radiation, followed by three weekly treatments using HDR brachytherapy with a 13-channel MC. Upper vagina was treated to 5 mm depth to 1500 cGy/3 fractions with a simultaneous integrated boost totaling 2100 cGy/3 fractions to tumor. Modeling of SC and Syed plans was performed using MC scans for each patient. Dosimetry for MC and SC plans was evaluated for PTV700 cGy coverage, maximum dose to 2 cm(3) to bladder, rectum, as well as mucosal surface points. Dosimetry for Syed plans was calculated for PTV700 cGy coverage. Patients were followed for treatment response and toxicity. RESULTS: Dosimetric analysis between MC and SC plans demonstrated increased tumor coverage (PTV700 cGy), with decreased rectal, bladder, and contralateral vaginal mucosa dose in favor of MC. These differences were significant (p < 0.05). Comparison of MC and Syed plans demonstrated increased tumor coverage in favor of Syed plans which were not significant (p = 0.71). Patients treated with MC had no cancer recurrence or >/=grade 3 toxicity. CONCLUSION: Use of MC was efficacious and safe, providing superior coverage of tumor volumes