Multiparametric MRI assessment of 6-month Post-Treatment response following Real-Time adaptive stereotactic body radiotherapy for prostate cancer: Correlation with Post-Treatment PSA kinetics.

Abstract

Focal dose intensification strategies targeting the dominant intra-prostatic lesion (DIL) improve outcomes of patients with prostate cancer. The purpose was to determine whether the 6-month multiparametric (mp)MRI response of the DIL is associated with post-treatment prostate-specific antigen (PSA) kinetics after MRI linear accelerator (LINAC) guided stereotactic body radiotherapy (SBRT) with focal dose intensification. Retrospective, single-center study including 72 patients with localized prostate cancer treated with MRI-LINAC SBRT with focal dose intensification and without androgen deprivation therapy. Patients were followed up at 6 months after SBRT with mpMRI and PSA. mpMRI complete response (CR) was defined as no residual lesion on diffusion-weighted imaging and dynamic contrast-enhanced MRI. This was correlated with PSA responses including PSA reduction (%), PSA reduction ≥ 50.0% (PSA₅₀), and PSA ≤ 1.0 ng/mL. mpMRI CR was achieved in 37 patients (51.4%) at 6 months. Patients with mpMRI CR had greater PSA reduction (81.8% vs 66.1%, p < 0.001), and more commonly had PSA₅₀ (100.0% vs 82.9%, p = 0.010) and PSA ≤ 1.0 ng/mL (45.9% vs 11.4%, p = 0.001) compared to those without mpMRI CR. In 10 patients without 6-month mpMRI CR but had further MRI follow-up (median 13 months), DILs either further decreased in size (30.0%) or resolved (70.0%). Initial 6-month mpMRI response correlates with PSA kinetics, which is associated with important clinical outcomes. mpMRI can be used for post-SBRT evaluation to gauge local tumor response of the DIL, where most recurrences occur.