L. L. Zhu1, J. S. Bredfeldt2,3, Y. H. Hu2,3, Y. Lyatskaya2, M. Czerminska2, C. Hancox2,3, S. Friesen2, C. V. Guthier3,4, S. Quirk2,3, P. L. Nguyen2,3, A. V. DAmico2,3, M. Sayan2,3, E. Kim2,3, K. W. Mouw2,3, M. T. King2,3, N. E. Martin2,3, and J. E. Leeman2,3; 1Harvard Radiation Oncology Program, Boston, MA, 2Department of Radiation Oncology, Brigham and Women’s Hospital/Dana-Farber Cancer Institute, Boston, MA, 3Harvard Medical School, Boston, MA, 4Department of Radiation Oncology, Dana-Farber Cancer Institute/Brigham and Women’s Hospital, Harvard Medical School, Boston, MA
Purpose/Objective(s): CT online adaptive (COA) radiotherapy allows daily personalization of radiotherapy plans based on cone beam CT imaging. With COA, daily imaging is acquired, target volume and normal tissue contours are adjusted, and a new treatment plan is generated for each fraction to account for daily anatomical changes. Presently, the impact of COA on toxicity outcomes remains unknown. This study aimed to examine the effect of COA on acute toxicity in patients receiving moderately hypofractionated radiotherapy for prostate cancer. Materials/
Methods: We analyzed the records of consecutive patients with prostate cancer treated to 60 Gy in 20 fractions in our department with either COA with daily plan adaptation or non-adaptive radiotherapy between 11/1/21 and 10/31/23. Dosimetry goals for target coverage and organs-at-risk were identical for COA and non-adaptive treatments. The planning margin employed for COA was slightly reduced (COA 4mm, non-adaptive 5mm). Toxicities were independently graded by two physicians using CTCAE v5.0 at baseline, at four weekly visits during radiotherapy, and at follow-up (60-180 days post-treatment) for the incidences of fatigue (grade 1+), gastrointestinal (GI, grade 1+) and genitourinary (GU, grade 2+) toxicities. Patient-reported outcomes during treatment were also evaluated. Univariate and multivariate logistic regression (controlling for hydrogel spacer use, use of androgen deprivation therapy (ADT), prostate volume, and age) were used to assess the effect of COA on the incidences of toxicity. Results: In total, 158 patients were analyzed, of whom 81 received COA and 77 received non-adaptive radiotherapy. Most patients had intermediate risk disease (6% low, 77% intermediate, 8% high, 9% metastatic). Hydrogel spacer usage was higher in the COA cohort (58% vs 40%, p=0.04) and ADT usage was lower in the COA cohort (57% vs 73%, p=0.05). On univariate analysis, COA was found to be significantly associated with reduced fatigue (50.6% vs 72.7%, OR 0.38, 95%CI 0.20-0.74, p=0.005), with a trend toward reduced GI toxicity (53.1% vs 66.2%, OR 0.58, 95%CI 0.30-1.09, p=0.09) and no significant association with GU toxicity (45.7% vs 53.2%, OR 0.73, 95%CI 0.39-1.38, p=0.34). On multivariate analysis, COA was found to be significantly associated with reduced fatigue (OR 0.27, 95%CI 0.13-0.58, p=0.001) and reduced GI toxicity (OR 0.47, 95%CI 0.23-0.95, p=0.04) and no association with GU toxicity (OR 0.67, 95%CI 0.33-1.32, p=0.25). Patient-reported toxicities were available for 40.5% of patients and showed similar trends to clinician-graded toxicities but were not statistically significant. Conclusion: To our knowledge, this study is the first comparison of clinical outcomes of patients receiving COA versus non-adaptive radiotherapy for prostate cancer. COA use is associated with decreased acute fatigue and GI toxicity but not GU toxicity. COA radiotherapy for prostate cancer warrants further investigation.
