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

Aim of this paper is to evaluate short and long-term changes in $T_2$ 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 $T_2$ relaxation times were calculated for quantitative analysis. The $T_2$ 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 $T_2$ values between the baseline and subsequent measurements, particularly between pre-therapy ($M_0$) and two weeks post-therapy ($M_1$), as well as during the monthly interval checks ($M_2$ - $M_6$). Some cases showed a delayed decrease in relaxation times, indicating the prolonged effects of therapy. The changes in $T_2$ values during the course of radiotherapy can help in monitoring radiotherapy response in unconfirmed patients, quantifying the scarring process, and recognizing the therapy failure.