Objective: A phase I-II prospective clinical trial of adjuvant accelerated radiation therapy (ADA-RT-1 trial) was set up in order to investigate the feasibility and efficacy of a pelvic conformal radiotherapy technique with concomitant boost (CB technique) to the vaginal vault in high-risk uterine cancers. Methods: Patients with uterine (endometrial cancer and sarcomas) and cervical neoplasm received external radiotherapy delivered in a short overall treatment time with a CB technique. The prescribed radiotherapy doses were 45/1.8 Gy/fraction to the pelvis and 55/2.2 Gy/fraction to the upper two-thirds of vagina plus resection lines in the parametria, respectively; treatment was administered in 25 fractions along 5 weeks. Results: This study included 91 consecutive gynecological cancer patients (endometrial = 72; cervical = 10; sarcoma = 9; median follow-up: 25 months, range: 5-72 months). Acute toxicity requiring treatment interruption (≥ grade 3) was observed in 7 patients (7.7%). No case of vaginal recurrence was documented. Actuarial 3-year loco-regional control rate was 97.7%, whereas 3-year disease-free survival and overall survival rates were 88.5% and 94.0%, respectively. Conclusion: In summary, the CB technique provides a high probability of local control with acceptable toxicity and shortening of the overall treatment time; moreover, it may offer some advantages to resource constrained medical environments.