Long-Term Outcomes of Stereotactic MRI-Guided Adaptive Radiation Therapy (SMART) for Prostate Cancer: Results From a Real-World Large Patient Cohort

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PURPOSE: Stereotactic magnetic resonance imaging-guided adaptive radiation therapy (SMART) has emerged as a treatment for localized prostate cancer with excellent acute toxicity outcomes. However, long-term outcomes have not been reported. This study reports on long-term outcomes of SMART for prostate cancer in a single institution. METHODS AND MATERIALS: We included consecutive patients with localized prostate cancer treated with SMART in an institutional prospective database comprising all risk categories. Treatment was delivered in 5 fractions of 7.25 Gy with daily online adaptation, preferably within 2 weeks. Acute and late toxicity as well as biochemical recurrences were routinely assessed during follow-up. Biochemical recurrence was defined by Phoenix criteria (prostate-specific antigen nadir + 2), and local, regional, or distant recurrence was confirmed by PSMA PET-CT imaging. RESULTS: From 2016-2021, 464 patients were analyzed. Median age was 72 years (range, 50-89) and the majority of patients had intermediate (50.0%) or high (44.8%) risk prostate cancer based on EAU guidelines. Acute gastrointestinal and genitourinary toxicity grade ≥2 rates were 5.2% and 19.8%, and cumulative late gastrointestinal and genitourinary toxicity grade ≥2 rates were 0.2% and 6.5%, respectively. After a median follow-up of 48.8 months (IQR, 36.3-63.5), 76 recurrences (16.4%) were recorded, most occurred in the high-risk group. Estimated 5-year freedom from biochemical or clinical failure for low-, intermediate-, and high-risk subgroups was 100% (95% CI, 100-100), 77.7% (95% CI, 68.2-84.7) and 74.9% (95% CI, 66.2-81.7), respectively. Incorporation of diagnostic imaging in tumor staging improved risk stratification and led to corresponding rates of 100% (95% CI, 100-100), 85.5% (95% CI, 76.6-91.2), and 71.6% (95% CI, 63.2-78.4). CONCLUSIONS: In this large cohort of patients with prostate cancer treated with SMART, acute and late toxicity was low. Biochemical and clinical control for high-risk patients was lower than for low- and intermediate-risk patients. Improved staging refines risk classification, guiding treatment intensification such as dose escalation in high-risk patients.

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