Proseven trial: MR-guided prostate stereotactic body radiotherapy in seven days - First results

Reducing the overall treatment duration of prostate SBRT has the potential to improve patient comfort and treatment compliance. Additionally, focal boosting to the gross tumor volume (GTV) is of interest to enhance oncologic outcomes. The phase II PROSEVEN trial (MR-guided prostate stereotactic body radiotherapy in seven days) combined both strategies, utilizing MR-guided radiotherapy (MRgRT) to deliver treatment.

Treatment delivered 36 Gy in five fractions to the planning target volume (PTV), 40 Gy to the clinical target volume (CTV), and up to 42 Gy as a simultaneous integrated boost (SIB) to the intraprostatic tumor (GTV). This was administered using a 0.35-Tesla MR-Linac over a seven-day period. The primary endpoint was the incidence of clinician-reported acute GU and GI toxicity of grade 2 or higher, assessed using CTCAE v5.0. Secondary endpoints included patient-reported outcomes (PROMs). This phase II Proseven trial, approved by the Ethics Committee of UZ Brussels, has completed recruitment with five-year follow-up ongoing.

A total of 132 patients with low (12.1 %), intermediate (66.6 %), and limited high-risk (21.2 %) prostate cancer were included. The median PSA at diagnosis was 9.43 ng/ml. SIB to the GTV was performed in 85 % of patients, and 64.4 % completed the treatment within the specified 7 days OTT. No grade 3 acute GU or GI toxicity was observed. Acute Grade 2 GU toxicity occurred in 35 %. Acute Grade 2 GI toxicity occurred in 5 %.

Prostate SBRT with SIB to the GTV in seven days using MRgRT demonstrated acceptable acute GU toxicity rates and low acute GI toxicity.