Purpose: The purpose of this study was to assess the potential of ^99mTc-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 ^99mTc-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.
Keywords: PSMA, DWI, prostate cancer, carbon ion radiotherapy