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Active surveillance of prostate cancer helps to avoid the side effects of curative treatments (surgery, radiotherapy, and brachytherapy) in patients with indolent disease. However, monitoring is invasive, requiring repeated biopsies that can be stressful. Since none of the standard prostate cancer treatments alter overall survival, preserving quality of life (QOL) remains the key objective. Stereotactic body radiation therapy (SBRT) of the prostate may be a treatment alternative to active surveillance. Moreover, unlike other such focused treatments, it does not require general anesthesia. This prospective monocenter Phase-II trial was conducted to study the feasibility and safety of SBRT for low-favorable intermediate-risk prostate cancer.

Patients were prospectively recruited in 2016–2019 if they had localized CAPRA score <3 prostate adenocarcinoma, an isolated PIRADS >4 macroscopic tumor on MRI, WHO Performance Status 0–1, no major urinary symptoms (IPSS ≤15). SBRT involved 36.25Gy (80% isodose prescription) delivered in 5 fractions every other day with Cyberknife-M6. Gross-target volume was delineated on MRI and validated by the same prostate cancer imaging radiology specialist. Primary outcome was delay between SBRT and initiation of a salvage treatment. Secondary outcomes were acute and late genitourinary and gastrointestinal (rectal) toxicity (assessed by CTCAEv4), biological, clinical, and MRI control, and QOL. QOL was assessed with IPPS, Urinary QOL (U-QOL), and International Index of Erectile Function (IIEF)5 Scale before treatment and at last follow-up.

In total, 24 patients were included. Median follow-up was 36 months. Salvage prostatectomy was never required. Three-year biochemical progression-free survival was 96% (23/24). The single biochemical recurrence was due to a small Gleason 6 (3+3) score, 2 mm-lesion in the non-irradiated lobe. Complete radiological response was found in all 19 patients who underwent one or more post-treatment MRI evaluations. Acute/late grade >3 toxicities did not occur: all acute toxicities were grade-1 genitourinary (38% of patients), grade-2 genitourinary (8%), or grade-1 rectal (13%) toxicities, and there was one (4%) transient late grade-1 genitourinary toxicity. QOL was unchanged at last follow-up, as shown by IPSS (the mean changed from 2.86 at baseline to 3.29, p>0.05), U-QOL (from 0.71 to 0.67, p>0.05), and IIEF5 (none of the 14 patients who were initially potent lost potency).

SBRT is a focused therapy that is feasible, well-tolerated, and preserves quality of life. This innovative robotized approach challenges other focused treatment alternatives as well as active surveillance.