Longitudinal ADC changes in prostate cancer patients treated with hypofractionated radiotherapy with 1.5T MR-Linac

Motivation: Additional functional information from DWI is one of the major advantages of MR-Linac over conventional radiation therapy techniques, and is sparsely studied. Goal(s): To monitor the ADC change during the course of hypofractionated radiation therapy in prostate cancer using a 1.5T MR-Linac. Approach: For each patient, a prostate DWI-EPI scan was acquired immediately after each of the 5 hypofractionated radiation therapy sessions. The ADC maps were generated and compared among the fractions using the Kruskal-Wallis test. Results: No significant ADC change among fractions might indicate that monitoring ADC alone might be insufficient to reflect the early treatment response. Impact: Biological radiotherapy treatment planning has been proposed for decades, but was hindered by lack of tools that could provide functional information with spatial interpretation. The study results shed light on potential use of DWI for early treatment monitoring using MR-Linac.