High-Risk Prostate Cancer and Radiotherapy: The Past and the Future. A Benchmark for a New Mixed Beam Radiotherapy Approach

Background: The prognosis for patients with high-risk prostate cancer is poor. No consensus exists on the most effective treatment. The aim of this retrospective study was to identify the biochemical progression-free survival and the toxicity profile of patients with localized high-risk prostate cancer treated with external beam radiation therapy. These results will constitute a benchmark for a prospective "mixed beam" trial: a boost with carbon ions followed by a pelvic photon intensity-modulated radiotherapy (NCT02672449 [clinicaltrials.gov]).

Patients and methods: We retrospectively reviewed the data of 76 patients treated in our institution with photon radiation therapy according to the inclusion criteria of the future "mixed beam" trial: cT3a and/or serum prostate-specific antigen > 20 ng/mL and/or Gleason score of 8 to 10, cN0 cM0. Toxicity, and biochemical and clinical progression-free survival were assessed.

Results: Seventy-six patients fulfilled our criteria. The median follow-up was 30.2 months (range, 7.2-61.1). Biochemical progression was observed in 22 patients (28.9%) after a median time of 20.2 months (range, 5-58.1) from the end of radiotherapy. Sixteen patients had clinical progression, in all the cases preceded by biochemical progression. Fifty-seven patients (75%) are alive with no evidence of disease, 13 (17.1%) are alive with clinically evident disease, 6 died (3 of prostate disease 3.9%).

Conclusion: Our results suggest that a more aggressive treatment is necessary. Local treatment intensification based on the "mixed beam" approach combining carbon ions (with its known radiobiological advantages) and photons might represent a promising strategy in high-risk prostate cancer and it will be investigated with our prospective clinical trial.