68Ga-PSMA PET/CT for monitoring response to 177Lu-PSMA-617 radioligand therapy in patients with metastatic castration-resistant prostate cancer

Purpose To evaluate the use of Ga-68-PSMA PET/CT for monitoring response to Lu-177-617 PSMA radioligand therapy in patients with metastatic castrate-resistant prostate cancer (mCRPC).Methods Patients from the University Hospital Bonn and the University Hospital Aachen were retrospectively reviewed for this study. We included 48 patients with mCRPC who were treated with Lu-177-PSMA-617 and whose records included Ga-68-PSMA PET/CT imaging before the first and after the third or fourth treatment cycle. A treatment response based on Ga-68-PSMA PET/CT was defined according to a modified version of the PERCIST criteria. A decline in PSA level of >= 50% was considered the reference standard. The sensitivity, specificity, positive and negative predictive values, and ROC curves were calculated, and patient survival times in relation to the PET results were also analysed.Results Ga-68-PSMA PET/CT had a sensitivity of about 85% and a specificity of between 55% and 65%. The negative and positive predictive values ranged between 70% and 78%. The fitted ROC area was 0.70. The survival time was about 19.6 months in patients with a treatment response, while nonresponders had a survival time of about 15.9 months. However, this difference between the groups was not statistically significant.Conclusion Our results indicate that Ga-68-PSMA PET/CT could be a useful tool for the evaluation of response to Lu-177-PSMA-617 radioligand therapy within a theranostic framework.