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Adjuvant radiation plays an important role in reducing locoregional recurrence in patients with uterine cancer. Although hypofractionated radiotherapy may benefit health care systems and the global community while decreasing treatment burden for patients traveling for daily radiotherapy, it has not been studied prospectively nor in randomized trials for treatment of uterine cancers, and the associated toxic effects and patient quality of life are unknown.To evaluate acute genitourinary and bowel toxic effects and patient-reported outcomes following stereotactic hypofractionated adjuvant radiation to the pelvis for treatment of uterine cancer.The Stereotactic Pelvic Adjuvant Radiation Therapy in Cancers of the Uterus (SPARTACUS) phase 1/2 nonrandomized controlled trial of patients accrued between May 2019 and August 2021 was conducted as a multicenter trial at 2 cancer centers in Ontario, Canada. In total, 61 patients with uterine cancer stages I through III after surgery entered the study.Stereotactic adjuvant pelvic radiation to a dose of 30 Gy in 5 fractions administered every other day or once weekly.Assessments of toxic effects and patient-reported quality of life (European Organisation for Research and Treatment of Cancer Quality of Life Questionnaires C30 and endometrial EN24) were collected at baseline, fractions 3 and 5, and at 6 weeks and 3 months of follow-up. Descriptive analysis was conducted, calculating means, SDs, medians, IQRs, and ranges for continuous variables and proportions for categorical variables. Univariate generalized linear mixed models were generated for repeated measurements on the quality-of-life scales.A total of 61 patients were enrolled (median age, 66 years; range, 51-88 years). Tumor histologic results included 39 endometrioid adenocarcinoma, 15 serous or clear cell, 3 carcinosarcoma, and 4 dedifferentiated. Sixteen patients received sequential chemotherapy, and 9 received additional vault brachytherapy. Median follow-up was 9 months (IQR, 3-15 months). Of 61 patients, worst acute gastrointestinal tract toxic effects of grade 1 were observed in 33 patients (54%) and of grade 2 in 8 patients (13%). For genitourinary worst toxic effects, grade 1 was observed in 25 patients (41%) and grade 2 in 2 patients (3%). One patient (1.6%) had an acute grade 3 gastrointestinal tract toxic effect of diarrhea at fraction 5 that resolved at follow-up. Only patient-reported diarrhea scores were both clinically (scores ≥10) and statistically significantly worse at fraction 5 (mean [SD] score, 35.76 [26.34]) compared with baseline (mean [SD] score, 6.56 [13.36]; P .001), but this symptom improved at follow-up.Results of this phase 1/2 nonrandomized controlled trial suggest that stereotactic hypofractionated radiation was well tolerated at short-term follow-up for treatment of uterine cancer. Longer follow-up and future randomized studies are needed to further evaluate this treatment.ClinicalTrials.gov Identifier: NCT04866394.