Postoperative Intensity-Modulated Radiotherapy in Low-Risk Endometrial Cancers: Final Results of a Phase I Study

Purpose To determine the maximum tolerated dose of short-course radiotherapy (intensity-modulated radiotherapy technique) to the upper two thirds of the vagina in endometrial cancers with low risk of local recurrence. Patients and Methods A Phase I clinical trial was performed. Eligible patients had low-risk resected primary endometrial adenocarcinomas. Radiotherapy was delivered in 5 fractions over 1 week. The planning target volume was the clinical target volume plus 5 mm. The clinical target volume was defined as the upper two thirds of the vagina as evidenced at CT simulation by a vaginal radio-opaque device. The planning target volume was irradiated by a seven-field intensity-modulated radiotherapy technique, planned by the Plato Sunrise inverse planning system. A first cohort of 6 patients received 25 Gy (5-Gy fractions), and a subsequent cohort received 30 Gy (6-Gy fractions). The Common Toxicity Criteria scale, version 3.0, was used to score toxicity. Results Twelve patients with endometrial cancer were enrolled. Median age was 58 years (range, 49–74 years). Pathologic stage was IB (83.3%) and IC (16.7%). Median tumor size was 30 mm (range, 15–50 mm). All patients completed the prescribed radiotherapy. No patient experienced a dose-limiting toxicity at the first level, and the radiotherapy dose was escalated from 25 to 30 Gy. No patients at the second dose level experienced dose-limiting toxicity. The most common Grade 2 toxicity was gastrointestinal, which was tolerable and manageable. Conclusions The maximum tolerated dose of short-course radiotherapy was 30 Gy at 6 Gy per fraction. On the basis of this result, we are conducting a Phase II study with radiotherapy delivered at 30 Gy.