Image-based three-dimensional conformal brachytherapy for medically inoperable endometrial carcinoma

Abstract

Purpose: Definitive radiotherapy is a viable option for medically inoperable patients with early stage endometrial cancer. We present our experience using image-based brachytherapy (BT). Methods and Materials: Patients with medically inoperable clinical Stage I endometrial adenocarcinoma received definitive BT with or without external beam radiotherapy. High-dose-rate BT was delivered using MRI- or CT-based planning for each fraction. For patients with an MRI, gross tumor volume (GTV) was contoured although dose was still prescribed to the clinical treatment volume (CTV), including the entire uterus, cervix, and upper 1-2cm of vagina. Equivalent 2Gy doses (EQD2) were calculated. Results: Thirty-eight patients were treated from 2007 to 2013, 20 receiving BT alone with a median dose of 37.5Gy in five to six fractions. For combined therapy, median external beam and BT doses were 45 and 25Gy in four to five fractions. With 15-month median followup, the 2-year actuarial local control and overall survival were 90.6% and 94.4%. No Grade 2-5 late toxicities were observed. Mean CTV D90 EQD2 for BT alone and combined therapy was 48.6±5.6 and 72.4±6.0Gy, whereas mean GTV D90 EQD2 was 172.3±59.6 and 138.0±64.6Gy. Conclusions: Image-based BT is feasible for medically inoperable early stage endometrial cancer with excellent early results. Despite low CTV doses, high doses delivered to GTV with BT likely accounts for high local control. Endometrial cancer guidelines for image-based planning are needed to define target volumes based on risk with differential dose delivery.