3217 - SBRT for Intermediate and High-Risk Prostate Cancer without Fiducials: A Phase II Clinical Trial
Presenter(s)
F. A. Almomen1, A. M. Alswilem1, B. A. Alruhaimi1, N. Almazrou1, A. Mohaimeed1, A. A. Alsuhaibani1, S. Aljabab2, and Y. M. Alayed3; 1Oncology Center, King Saud University Medical City, Riyadh, Saudi Arabia, 2Radiation Oncology, College of Medicine, King Saud University, Riyadh, Saudi Arabia, 3Radiation Oncology Unit, College of Medicine, King Saud University, Riyadh, Saudi Arabia
Purpose/Objective(s): The role of stereotactic body radiotherapy (SBRT) in prostate cancer treatment is well established. However, most of the evidence is from high-volume hospitals with access to resources such as advanced machines or implanted fiducials. Here we report the outcomes of a phase II prostate SBRT clinical trial from a small academic center with limited resources.
Materials/Methods: Patients with intermediate or high-risk prostate cancer were enrolled in a prospective phase II SBRT trial at a low-volume hospital. The clinical target volume (CTV) included the prostate only, and the planning target volume (PTV) was a 4mm expansion on the CTV. The dose prescribed was 40 Gy in 5 fractions, either weekly or every other day. CBCT was used for image guidance without fiducials. The primary endpoint was late CTCAE toxicity. Secondary endpoints included acute toxicity, biochemical failure, and quality of life (EPIC). Patients had risk-adapted androgen deprivation therapy as per standard of care.
Results: Thirty-nine patients were treated, with a median age of 76.1 years; 71.8% (n=28) had high-risk disease, and median baseline PSA was 17.1 ng/mL. Cumulative worst acute grade 2 gastrointestinal (GI) toxicity occurred in 7.7% of patients, with no grade =3 events. No acute grade =2 genitourinary (GU) toxicity was observed. Late toxicity remained low, with cumulative grade 2 GI and GU toxicity observed in 5.3% and 2.6% of patients, respectively, and no grade =3 events.
Patient-reported quality of life demonstrated distinct decline and recovery patterns across domains over time. Urinary scores declined by 6.9 points at 6 months, with recovery to baseline by 24 months. Bowel scores showed minimal fluctuation, ranging from -1.8 to +3.6 points. Hormonal scores declined by 11.4 points at 6–12 months, returning to baseline by 30 months. Sexual scores decreased by 11.6 points at 12-24 months, with late recovery ranging from -2.5 to +2.9 points at 36–60 months. At a median follow-up of 61 months, median PSA nadir was 0.02 ng/mL, achieved at a median of 12 months. Biochemical failure occurred in three patients. One patient developed local recurrence, none developed regional nodal recurrence, and two developed distant metastases. Three deaths occurred during follow-up, one of which was to prostate cancer in a patient with metastatic progression. Five-year event-free survival was 87.2%.Conclusion: SBRT for intermediate and high-risk prostate cancer without fiducials was minimal and well tolerated. Patient-reported EPIC outcomes demonstrated mild to moderate early declines across domains, with recovery to baseline over time. Oncologic outcomes were favorable and comparable to published studies. Given the relatively small sample size, larger studies and longer follow-ups are recommended. However, the results are encouraging for adopting prostate SBRT in small centers with limited resources.