The XXXXX trial ran as 3 parallel single-center phase II non-randomized trials in 3 different institutes. Each institute enrolled 20 patients who were all treated on a 1.5T Unity MR-Linac. The GTV was defined as tumor(s) visible on multi-parametric MRI. The CTV was defined as the whole prostate. The proximal 1-2 cm of seminal vesicles were included in the CTV at the clinician's discretion. An intra-prostatic margin of 4 mm was applied to the GTV to account for delineation and pathological uncertainty (GTV4mm) and no PTV margin was applied to the CTV. All patients were treated with 30 Gy in 5 fractions to the CTV and an isotoxic boost of 45 Gy to the GTV4mm. The primary endpoint was technical feasibility defined as accumulated GTV D90% of >42Gy on the post-treatment MRI in ≥90% of the patients.
While toxicity-minimizing radiotherapy in online adaptive MRI-guided SBRT for PCa was feasible in 2 of the 3 institutes, robust coverage of the GTV and CTV could not be assured in the absence of a gating strategy.
Between May 2023 and September 2024, 60 patients were treated of which 54 were included for analysis. An accumulated GTV D90% of >42 Gy was reached in 46 patients (85%). Analysis per institute showed that this criterion was reached in 10 of 14 patients (71%) in institute 1 and in 18 of 20 patients (90%) in both institute 2 and 3.
Escalating dose to the gross tumor volume (GTV) whilst de-escalating dose to the prostate clinical target volume (CTV) and using a 0 mm PTV margin can potentially minimize toxicity without compromising biochemical control in patients with intermediate-risk prostate cancer (PCa). We evaluated the technical feasibility of this approach in online adaptive MRI-guided stereotactic body radiation therapy (SBRT).
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