Outcome of the first 200 patients with prostate cancer treated with MRI-Linac at Assuta MC.

Background: We present our experience with MR-guided stereotactic body radiotherapy (SBRT) for 200 consecutive patients with prostate cancer with minimum 3-month follow-up. Methods: Treatment planning included fusion of the 0.35-Tesla planning MRI with multiparametric MRI and PET-PSMA for Group Grade (GG) 2 or higher and contour review with an expert MRI radiologist. No fiducials or rectal spacers were used. Prescription dose was 36.25 Gy in 5 fractions over 2 weeks to the entire prostate with 3-mm margins. Daily plan was adapted if tumor and organs at risk (OAR) doses differed significantly from the original plan. The prostate was monitored during treatment that was automatically interrupted if the target moved out of the PTV range. Results: Mean age was 72 years. Clinical stage was T1c, 85.5%; T2, 13%; and T3, 1.5%. In addition, 20% were GG1, 50% were GG2, 14.5% were GG3, 13% were GG4, and one patient was GG5. PSA ranged from 1 to 77 (median, 6.2). Median prostate volume was 57cc, and 888/1000 (88%) fractions required plan adaptation. The most common acute GU toxicity was Grade I, 31%; dysuria and acute gastrointestinal toxicity were rare. Three patients required temporary catheterization. Prostate size of over 100cc was associated with acute fatigue, urinary hesitance, and catheter insertion. Prostate Specific Antigen (PSA) decreased in 99% of patients, and one patient had regional recurrence. Conclusion: MR-guided prostate SBRT shows low acute toxicity and excellent short-term outcomes. Real-time MRI ensures accurate positioning and SBRT delivery.