Daily online adaptive radiotherapy of postoperative endometrial and cervical cancer with PTV margin reduction to 5 mm: dosimetric outcomes, acute toxicity, and first clinical experience

Purpose This study evaluated the first clinical implementation of daily iterative cone-beam computed tomography (iCBCT)-guided online adaptive radiotherapy (oART) in the postoperative treatment of endometrial and cervical cancer. Methods and Materials Seventeen consecutive patients treated with daily iCBCT-guided oART were enrolled in this prospective study, with a reduced uniform three-dimensional PTV margin of 5 mm. Treatment plans were designed to deliver 45 or 50.4 Gy in 1.8 Gy daily fractions to PTV. Pre- and posttreatment ultrasound and iCBCT scans were performed to record intrafractional bladder and rectal volume changes. The accuracy of contouring, oART procedure time, dosimetric outcomes and acute toxicity were evaluated. Results The average time from first iCBCT acquisition to completion of treatment was 22 min and 26 s. During this period, bladder volume increased by 44 cm3 using iCBCT contouring, while rectal volume remained stable (62.9 cm3 pretreatment vs. 61.9 cm3 posttreatment). A total of 91.6% of influencers and 88.1% of CTVs required no or minor edits. The adapted plan was selected in all (434) fractions and significantly improved the dosimetry coverage for CTV and PTV, especially the vaginal PTV coverage by nearly 7% (p<0.05). The adapted bladder Dmean was 104.61 cGy, and the rectum Dmean was 123.67 cGy, significantly lower than the scheduled plan of 108.24 and 128.19 cGy, respectively. The bone marrow, femur head left and right dosimetry were also improved with adaptation. Grade 2 acute gastrointestinal and genitourinary toxicities were 24% and 0, respectively. There was a Grade 3 acute toxicity of decreased white blood cell count in one patient. Conclusions Daily oART was associated with favourable dosimetry improvement and low acute toxicity, supporting its safety and efficacy for postoperative treatment of endometrial and cervical cancer. These results need to be validated in a larger prospective randomized controlled cohort.