MRI-guided focal proton radiation therapy for locally advanced prostate cancer

We investigate the dosimetric efficacy and clinical implications of proton radiation therapy of prostate cancer with dose microboost to the MRI-defined dominant intraprostatic lesions (DIL).
For 6 patients with high-risk prostate cancer, DILs were delineated using multiparametric MRI based on hypointense appearance on T2-weighted and apparent diffusion coefficient maps. After transferring the contours to CT via image registration, conventional and boosted pencil beam scanning proton treatment plans were created. Dose-volume histograms were analyzed. Tumor control probability (TCP) and normal tissue complication probability (NTCP) were compared between the two scenarios.
In all cases the addition of up to 60% (of prescribed dose) boost to the DILs was achievable without violating the organs at risk (OAR) planning constraints. The increase in OAR mean dose was within 1.5 Gy, and all volume indices remained within clinical tolerance for all cases. TCP of DILs increased by at least 59% depending on the boost amount and model parameters. Bladder and rectum NTCP increase remained negligible.
Proton therapy of high-risk prostate cancer with MRI-guided focal boost to highly malignant DILs is feasible and could yield significant improvement in treatment outcome without increasing toxicities.