Dosimetric predictors of local control and complications in gynecologic transperineal implant patients: The medical college of wisconsin experience.

ABSTRACT

PURPOSE: Investigate the relationship between dosimetric parameters with local control (LC) and complications following transperineal high-dose rate (HDR) interstitial brachytherapy (ISBT) for gynecologic (GYN) malignancies. METHODS AND MATERIALS Between 2001 and 2016, 59 patients were treated for primary or recurrent GYN malignancies. Most patients received external beam irradiation, followed by transperineal ISBT via the Syed-Neblett applicator set with CT-based planning. Treatment plans were retrospectively reviewed to evaluate for an association among LC or toxicity with the equivalent dose at 2 Gy per fraction (EQD2) for the clinical target volume (CTV), 0.1 cc (D0.1cc), and 2 cc (D2cc) volumes of the organs at risk (OAR), low/high dose volumes for the OAR and CTV, and ratio of dose at the core vs. the implant periphery. RESULTS: The median follow-up among survivors was 24 months. 34% of patients had a component of local failure and in 12%, this was isolated. Late grade 3 (G3) toxicity occurred in 15% of patients. There were no G4-5 toxicities. Rectal D0.1cc > 75 Gy trended toward significance in predicting the development of non-fistula late G2-3 rectal complications. Bladder D0.1cc > 94 Gy significantly predicted for the development of late G2-3 vesicovaginal fistula formation. The ratio of the total dose at the vaginal surface to the needle periphery above 121% trended in predicting for any complication or fistula formation. CONCLUSIONS: HDR ISBT combined with EBRT achieved LC in 66% of patients with advanced or recurrent GYN cancers. Rectal and bladder D0.1cc doses may be predictive of complications as may the ratio of the implant dose at the core vs. periphery.