Online adaptive MRI-guided SBRT showed technical feasibility in intermediate-risk prostate cancer patients.
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Key Takeaway
Consider online adaptive MRI-guided SBRT as a feasible option for intermediate-risk prostate cancer in specialized centers.
This Phase 2 non-randomized trial evaluated online adaptive magnetic resonance imaging (MRI)-guided stereotactic body radiation therapy in a population of 54 patients with intermediate-risk prostate cancer. The study design involved 3 parallel single-center trials conducted across 3 different institutes. The intervention utilized escalating doses to the gross tumor volume and de-escalating doses to the prostate clinical target volume using a 0-mm planning target volume margin.
The primary outcome was technical feasibility, defined as an accumulated gross tumor volume D90% greater than 42 Gy on post-treatment MRI in at least 90% of patients. This threshold was reached in 46 of 54 patients, representing 85% of the analyzed cohort. When stratified by institute, the outcome was achieved in 10 of 14 patients (71%) at institute 1 and 18 of 20 patients (90%) at institutes 2 and 3.
Safety and tolerability data were not reported in the study. A key limitation noted was that robust coverage of the gross tumor volume and clinical target volume could not be assured in the absence of a gating strategy. Because the study was non-randomized and lacked a comparator, causal conclusions regarding efficacy cannot be drawn. These results indicate technical feasibility but highlight the need for further investigation in randomized settings.
View Original Abstract ↓
PURPOSE: Escalating dose to the gross tumor volume (GTV) while de-escalating dose to the prostate clinical target volume (CTV) and using a 0-mm planning target volume margin can potentially minimize toxicity without compromising biochemical control in patients with intermediate-risk prostate cancer. We evaluated the technical feasibility of this approach in online adaptive magnetic resonance imaging (MRI)-guided stereotactic body radiation therapy.
METHODS AND MATERIALS: The DESTINATION-MRL trial ran as 3 parallel single-center phase 2 non-randomized trials in 3 different institutes. Each institute enrolled 20 patients who were all treated on a 1.5T Unity MR-linear accelerator (MR-Linac). The GTV was defined as tumor(s) visible on multiparametric MRI. The CTV was defined as the whole prostate. The proximal 1-2 cm of the seminal vesicles were included in the CTV at the clinician's discretion. An intraprostatic margin of 4 mm was applied to the GTV to account for delineation and pathological uncertainty (GTV 4 mm) and no planning target volume 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 GTV 4 mm. The primary endpoint was technical feasibility, defined as an accumulated GTV D90% of >42 Gy on the post-treatment MRI in ≥90% of the patients.
RESULTS: 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 institutes 2 and 3.
CONCLUSIONS: Although toxicity-minimizing radiation therapy in online adaptive MRI-guided stereotactic body radiation therapy for prostate cancer 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.
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