Combination of (99m)Tc-Labeled PSMA-SPECT/CT and Diffusion-Weighted MRI in the Prediction of Early Response After Carbon Ion Therapy in Prostate Cancer: A Non-Randomized Prospective Pilot Study

PURPOSE: The purpose of this study was to assess the potential of (99m)Tc-labeled PSMA-SPECT/CT and diffusion-weighted image (DWI) for predicting treatment response after carbon ion radiotherapy (CIRT) in prostate cancer. PATIENTS AND METHODS: We prospectively registered 26 patients with localized prostate cancer treated with CIRT. All patients underwent (99m)Tc-labeled PSMA-SPECT/CT and multiparametric magnetic resonance imaging (MRI) before and after CIRT. The tumor/background ratio (TBR) and mean apparent diffusion coefficient (ADC(mean)) were measured on the tumor and the percentage changes before and after therapy (ΔTBR and ΔADC(mean)) were calculated. Patients were divided into two groups: good response and poor response according to clinical follow-up. RESULTS: The median follow up time was 38.3months. The TBR was significantly decreased (p=0.001), while the ADC(mean) was significantly increased compared with the pretreatment value (p<0.001). The ΔTBR and ΔADC(mean) were negatively correlated with each other (p = 0.002). On ROC curve analysis for predicting treatment response, the area under the ROC curve (AUC) of ΔTBR (0.867) for predicting good response was higher than that of ΔADC(mean) (0.819). The AUC of combined with ΔTBR and ΔADC(mean) (0.895) was higher than that of either ΔADC(mean) or ΔTBR alone. The combined use of ΔTBR and ΔADC(mean) showed 91.4% sensitivity and 95.2% specificity. CONCLUSION: Our preliminary data indicate that the changes of TBR and ADC(mean) maybe an early bio-marker for predicting prognosis after CIRT in localized prostate cancer patients. In addition, the ΔTBR seems to be a more powerful prognostic factor than ΔADC(mean) in prostate cancer treated with CIRT.