KEY POINTS
- This prospective multicenter phase II study enrolled 76 patients at four Canadian hospitals between 2018 and 2020. 37% had unfavorable-intermediate-risk and 63% high-risk prostate cancer, with a median follow-up of 62.8 months.
- Treatment compressed both prostate and elective pelvic nodal irradiation into five weekly fractions. All patients received 25 Gy in 5 fractions to elective pelvic nodes; the prostate received either 40 Gy in 5 fractions, or 35 Gy in 5 fractions with an MRI-defined intraprostatic boost up to 50 Gy. All received androgen deprivation therapy for 6 months in unfavorable-intermediate-risk disease and 12–18 months for high-risk disease.
- A focal intraprostatic boost was delivered in 31 patients (41%), with a median dominant-lesion D99 of 46.4 Gy. The protocol used VMAT, implanted fiducials and pre- and post-treatment CBCT, with a 6-mm pelvic nodal PTV margin and 3-mm prostate margin.
- Acute grade ≥2 gastrointestinal toxicity occurred in only 4.1%, while grade ≥2 genitourinary toxicity occurred in 18%. At the latest five-year assessment, grade 2 gastrointestinal and genitourinary toxicity was present in just 2.9% and 4.3%, respectively, with no grade ≥3 GI or GU toxicity at last follow-up.
- Biochemical failure occurred in 6 patients, and the cumulative probability of biochemical failure at five years was 10.5%, corresponding to approximately 90% biochemical disease control. Only one patient developed metastatic disease, and one of nine deaths during follow-up was attributed to prostate cancer.
- PSA kinetics were particularly informative. Median PSA nadir was 0.2 ng/mL, reached after a median 19.6 months. 70.5% achieved PSA <0.4 ng/mL at four years; none of these patients subsequently experienced biochemical failure versus 34% among patients who did not reach that threshold (p=0.0002).
- Testosterone recovered to the study-defined normal level in 84% of patients, with a median recovery time of 14.3 months after the final ADT dose. At five years, mean EPIC urinary, bowel and sexual scores had returned close to baseline, with large long-term quality-of-life deterioration reported in only 2.9%, 5.9% and 4.6%, respectively.
CLINICAL TAKEAWAY
Treating the prostate and elective pelvic nodes in only five weekly fractions, with an optional focal boost up to 50 Gy, produced encouraging five-year control without a major late GI/GU toxicity signal. The dataset is substantially more mature than a simple feasibility report, but the trial remains non-randomized and cannot establish whether elective nodal treatment or the focal boost improves outcomes; ongoing phase III validation matters.