3386 - Stereotactic Magnetic Resonance-Guided Adaptive Radiotherapy for Prostate Cancer from Prospective Phase II Trial: Prostate vs. Prostate, pElvis and Metastases (SMART-P vs. SMART-PEM)
Presenter(s)
M. Sun1, S. Qin1, R. Wei1, Y. Tian1, L. L. Yan1, W. Xia1, Z. Liu1, Q. Fu1, Y. W. Song1, H. Fang1, H. Jing1, S. Wang1, Y. X. Li1, N. Z. Xing2,3, and N. N. Lu1,2; 1Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, 2Beijing Key Laboratory of Urologic Cancer Cell and Gene Therapy, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, 3Department of Urology and State Key Laboratory of Molecular Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China
Purpose/Objective(s): To evaluate the physician- and patient-reported outcomes of stereotactic MR-guided adaptive radiotherapy (SMART) for prostate cancer w/o pelvic and metastatic irradiation.
Materials/Methods: In this prospective phase II study, 102 patients with histopathologically confirmed prostate cancer were treated with SMART on a 1.5-T MR-linac between February 2021 and November 2025. Radiotherapy was delivered in five alternate-day fractions using an adapt-to-shape (ATS) workflow. Patients treated with prostate with pelvis and metastases were grouped as PEM group, otherwise P group. At baseline, patients enrolled in P group should maintain a bladder volume of 150 mL for 30 min, compared to 250 mL for 60 min in the PEM group. The primary endpoint was clinician-reported acute grade =2 genitourinary (GU) and gastrointestinal (GI) toxicity within 12 weeks, assessed by CTCAE v5.0. Secondary endpoints included late toxicity (RTOG criteria), quality of life (QoL; IPSS, EPIC-26, FACT-P, EORTC QLQ-C30, IIEF-5), and survival outcomes.
Results: In all, there’re 37 and 65 patients in PEM and P groups, respectively. The median on-couch time was 36 minutes (range, 24–80), 59 minutes (range, 35–80) and 33 minutes (range, 24–46) for whole cohort, PEM and P groups. The PEM group had fewer patients with baseline lower urinary tract symptoms (LUTS), and more patients using prophylactic solifenacin and rectal lavage during treatment and 1 week thereafter (solifenacin: 59.5% vs.32.3%, rectal lavage: 94.6% vs.46.2%). No spacer was used for whole group. At baseline, G1 and G2 GU toxicities were observed in 19 (29.2%) and 4 (6.2%) patients in the P group, respectively, compared to 11 patients (29.7%) and 0 with G1 and G2 GU toxicity in the PEM group. For acute toxicities, the incidence of =G2 GU events was higher in the P group [13 (20.0%) vs. 2 (5.4%)], including one G3 case (1.5%). The rates of =G2 acute GI events were comparable between P and PEM groups [5 (7.7%) vs. 2 (5.4%)], with one G3 case (2.7%) in the latter. No grade =2 late GI toxicity occurred in either group, while one case of G2 late GU toxicity was noted in the P group. QoL scores declined at 2 weeks post-treatment but returned to baseline around 3 months, with no difference between two groups. With median follow-up time of 13.5 (4.3–40.3) months and 17.9 (3.1–57.6) months for PEM and P groups, the 2-year biochemical and clinical progression-free survival rates were both 88.4% in the PEM group, compared to 100% in the P group (P < .001). The in-field control rate was 100% for both treatment groups.
Conclusion: For highly selected patients with minimal baseline LUTS, SMART-PEM was well tolerated, with acute and late toxicities non-inferior to those observed in patients receiving prostate w/o seminal vesicles RT, particularly when prophylactic medication was used. These results support further evaluation in large matched cohort.