ESTRO 2025 - Abstract Book

S2062

Clinical - Urology

ESTRO 2025

One-hundred prostate cancer patients underwent MRgART on the Unity MR-Linac were prospectively recruited to this ethics approved study. Prescription used was 36.25Gy to PTV, 38 to 40Gy to CTV and a DiL boost of 42 to 45 Gy was used at clinician’s discretion, adhering to strict OAR constraints. Patient baseline summary can be seen in Table 1. Real-time adaptive plans were generated for each fraction, with doses to targets and OARs reviewed and approved before treatment delivery. Gastrointestinal (GI) and genitourinary (GU) toxicity were recorded at 3 months and a median of 15 months as per Common Terminology Criteria for Adverse Effects (CTCAE) v.5, alongside prostate-specific antigen (PSA) levels.

Results:

All daily adaptive plans met target coverage and OAR constraints. At 3 months, 31% of patients experienced acute GU toxicity, with the majority G1 at 30% (30/100) and G2 was recorded at 1% (1/100). One patient experienced Grade 4 GU toxicity, with CTV prescribed to 38Gy and no DiL boost. At the median 15-month follow-up, the late G1 and G2 toxicity was recorded in 27% (27/100) and 5% (5/100) of patients respectively. Higher G2 acute GU toxicity was observed in SIB to DIL group at 38.7% (12/31) vs non-SIB at 27% (20/49) respectively. One patient developed a late G3 toxicity who was prescribed 40Gy to CTV and 42Gy to DiL (Figure 1). Overall, the acute and late GI toxicity were 7% and 5% respectively. Excluding 17 patients on androgen deprivation therapy, PSA levels for remaining patients exhibited a significant drop of 69.5% at 3 months and 87.4% at 15 months. Conclusion: MRI-guided dose-escalated prostate radiotherapy is effective and safe with acceptable toxicities. Longer-term follow-up of patients receiving SIB is needed to verify its safe toxicity profile.

Keywords: MRI guided stereotactic prostate radiotherapy

References: References:

[1] Leeman JE, Shin KY, Chen YH, et al. Acute toxicity comparison of magnetic resonance-guided adaptive versus fiducial or computed tomography-guided non-adaptive prostate stereotactic body radiotherapy: A systematic review and meta-analysis. Cancer . 2023;129(19):3044-3052. doi:10.1002/cncr.34836 [2] Kerkmeijer LGW, Groen VH, Pos FJ, et al. Focal Boost to the Intraprostatic Tumor in External Beam Radiotherapy for Patients With Localized Prostate Cancer: Results From the FLAME Randomized Phase III Trial. J Clin Oncol . 2021;39(7):787-796. doi:10.1200/JCO.20.02873