Quantitative single-photon emission computed tomography/computed tomography in assessing the effectiveness of radium-223 dichloride therapy

Background. Systemic radionuclide therapy (RNT) with radium-223 was approved for treatment of bone metastases in patients with metastatic castration-resistant prostate cancer (mCRPC) based on the results of the phase III ALSYMPCA trial. Radium-223 increases overall survival and improves quality of life of the patients. At the moment, there is no unified algorithm for assessing the effectiveness of radium-223 dichloride therapy using modern diagnostic methods, one of which is quantitative single-photon emission computed tomography/computed tomography (SPECT/CT).Aim. To determine the capabilities of quantitative SPECT/CT in assessing the effectiveness of radium-223 dichloride therapy in patients with bone metastases of CRPC.Materials and methods. The study included 30 patients who received a full course (6 injections) of RNT with radium-223, who before and after therapy underwent PET/CT with prostate-specific membrane antigen (PSMA) ligands and skeletal scans, including quantitative SPECT/CT of the whole body; before each RNT cycle, blood parameters, tumor marker prostate-specific antigen, clinical status, and severity of pain were measured. A comparison and correlation analysis of quantitative parameters of the bone-seeking radiopharmaceutical accumulation, biochemical markers, clinical status, and pain syndrome measured using a visual analogue scale, were performed.Results. Comparison of the quantitative characteristics of bone-seeking radiopharmaceutical accumulation in the skeletal bones before and after RNT showed that only the maximal standardized uptake value (SUVmax) decreased significantly in 25 of 30 patients (p = 0.000215). Considering prostate-specific antigen levels, starting from the 3rd course it waspossible to statistically reliably establish further dynamics of changes in this marker (p 0.05). When analyzing groups of patients divided depending on the changes in pain syndrome per the VAS scale, a decrease in SUVmean and pain syndrome was detected in 13 (59.1 %) patients. Without changes in pain syndrome intensity, SUVmean decreased in 9 (40.9 %). The differences in indicators were statistically significant (p = 0.008).Conclusion. There is a tendency towards a decrease in the quantitative indicators of radiopharmaceutical accumulation after systemic RNT with radium-223 dichloride. The relationship between quantitative indicators of the bone-seeking radiopharmaceutical accumulation, laboratory parameters and clinical status is observed. However, each of the analyzed indicators separately does not fully reflect the effectiveness of the therapy.In the future, quantitative SPECT/CT may become more widely used not only for selecting patients for systemic RNT with radium-223 dichloride, but also for assessing its effectiveness since it provides objective view of the distribution pattern of radiopharmaceutical in areas of metastasis and correlates with other assessment methods. It can also become an important prognostic factor in monitoring the condition of patients with mCRPC.