Feasibility of longitudinal prostate R₂ ^⁎ measurements in patients undergoing stereotactic ablative radiotherapy on an MRI-linac.

Authors

Chris Moore, Asher Ezekiel, Vodathi Bamunuarachchi, Ereny Saad, Anubhav Datta, Peter Hoskin, Ananya Choudhury, Marcel van Herk, David L Buckley, Michael J Dubec, Damien J McHugh

Published in

Physics and imaging in radiation oncology. Volume 41. Pages 101103. Epub Oct 06, 2026.

Abstract

Tissue R₂* (1/T₂*), sensitive to deoxyhaemoglobin, is a proposed hypoxia biomarker in prostate cancer. This exploratory work investigates prostate R₂* and volume throughout and after hypo-fractionated radiotherapy and the effects of androgen deprivation therapy (ADT).
Fifteen patients (seven with ADT) received five-fraction stereotactic-ablative-radiotherapy (SABR) on a 1.5 T Elekta Unity MRI-linac, with R₂* mapping at MR-Simulation and treatment visits 1, 3, 5. Six patients had follow-up imaging post-treatment.Treatment-induced whole-prostate and tumour R₂*/volume differences were investigated using repeated-measures analysis-of-variance.ADT effects on baseline whole-prostate R₂*/volume were investigated using unpaired t-tests. Spearman correlations between whole-prostate R₂* and volume were calculated before and during treatment.
Whole-prostate R₂* (mean difference [95% CIs] = -1.77 [-2.17 to -0.498] s^-1, p = 0.003) and tumour R₂* (-3.11 [-5.78 to -1.44] s^-1, p = 0.003) decreased, whole-prostate volume (8.05 [4.76 to 11.7] cm³) increased after two fractions.Follow-up whole-prostate R₂* (p = 0.62) and volume (p = 0.16) were not significantly different from baseline.ADT patients had higher baseline whole-prostate R₂* (p = 0.006) and lower volume (p = 0.003). ADT did not impact treatment-induced changes (p = 0.51).Baseline whole-prostate R₂*/volume were negatively correlated (r = -0.75, p = 0.002); treatment-induced R₂*/volume changes were not correlated r = 0.44, p = 0.11).
Treatment-induced whole-prostate and tumour R₂* changes were measured after two SABR fractions. Post-treatment whole-prostate R₂* and volume were not significantly different from baseline.Further work is required to confirm the mechanism(s) causing observed treatment effects.

PMID:
42893191
Bibliographic data and abstract were imported from PubMed on 18 Oct 2026.

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