MRI-guided adaptive stereotactic body radiotherapy for the prostate bed: a prospective study of safety, tolerability, and patient-reported quality-of-life outcomes.

BACKGROUND AND

OBJECTIVES

Magnetic resonance-guided radiotherapy (MRgRT) applied as stereotactic body radiotherapy to the prostate bed represents an emerging post-prostatectomy treatment approach, offering superior soft-tissue visualization and the potential for daily online adaptive planning. This study reports a prospective experience with MR-guided adaptive SBRT to the prostate bed, with a primary focus on treatment-related adverse events and patient-reported quality-of-life (QoL) outcomes.

MATERIALS AND

METHODS

A prospective cohort of 31 patients with biochemical recurrence following radical prostatectomy was treated with MR-guided adaptive SBRT (32.5 Gy in 5 fractions) using a 0.35 T MR-LINAC (MRIdian®, ViewRay). Elective pelvic nodal irradiation was delivered in 42% of patients (25 Gy in 5 fractions), and a simultaneous integrated boost (SIB) to macroscopic disease (35 Gy in 5 fractions) was administered in 9.7% of cases. Concomitant androgen deprivation therapy (ADT) was administered in 77.4% of patients. Adverse events were graded according to the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0, and patient-reported outcomes were assessed using the Expanded Prostate Cancer Index Composite-26 (EPIC-26) and the International Prostate Symptom Score (IPSS).

RESULTS

With a median follow-up of 8.8 months (IQR: 6.1-16.8), no grade ≥ 3 adverse events were observed at any time point. Acute grade ≥ 2 genitourinary (GU) adverse events were 3.3% at treatment completion (1/30) and 4.3% at 6 months (1/23), with low-grade urinary incontinence as the predominant event. "No grade ≥ 2 gastrointestinal (GI) adverse events were observed throughout the follow-up period.EPIC-26 urinary domain scores were preserved over time (baseline: 79.6; 6 months: 81.5), while bowel domain scores remained consistently at ceiling levels (median 100 points at all time points). Median prostate-specific antigen (PSA) declined from 0.31 ng/mL pre-treatment to 0.02 ng/mL at 6 months, with continued suppression at 12 months (0.04 ng/mL, n = 11). Biochemical response was 100% (31/31), although interpretation is limited by the short follow-up.

CONCLUSIONS

MRgRT to the prostate bed demonstrates a favorable early safety and tolerability profile, with no grade ≥ 3 adverse events, low rates of grade ≥ 2 GU adverse events (4.3% at 6 months, 1/23), and absence of late grade ≥ 3 GI adverse events, while maintaining patient-reported QoL outcomes.