Longitudinal analysis of T2 relaxation time variations following radiotherapy for prostate cancer

Abstract

Aim of this paper is to evaluate short and long-term changes in 𝑇2 relaxation times after radiotherapy in patients with low and intermediate risk localized prostate cancer. A total of 24 patients were selected for this retrospective study. Each participant underwent 1.5T magnetic resonance imaging on seven separate occasions: initially after the implantation of gold fiducials, the required step for Cyberknife therapy guidance, followed by MRI scans two weeks post-therapy and monthly thereafter. As part of each MRI scan, the prostate region was manually delineated, and the 𝑇2 relaxation times were calculated for quantitative analysis. The 𝑇2 relaxation times between individual follow-ups were analyzed using Repeated Measures Analysis of Variance that revealed a significant difference across all measurements (F (6, 120) = 0.611, p << 0.001). A Bonferroni post hoc test revealed significant differences in median 𝑇2 values between the baseline and subsequent measurements, particularly between pre-therapy (𝑀0) and two weeks post-therapy (𝑀1), as well as during the monthly interval checks (𝑀2 - 𝑀6). Some cases showed a delayed decrease in relaxation times, indicating the prolonged effects of therapy. The changes in 𝑇2 values during the course of radiotherapy can help in monitoring radiotherapy response in unconfirmed patients, quantifying the scarring process, and recognizing the therapy failure.