Response to 223RaCl2 or 177Lu-iPSMA treatment in bone metastases due to castration-resistant prostate cancer as a function of absorbed dose

Abstract

A newer therapy for the treatment of bone metastases due to castration-resistant prostate cancer (mCRPC) is the administration of 223Ra-dichloride (223RaCl2) or 177Lu-iPSMA. Both radionuclides have a gamma emission, but the response to the treatment is not obtained by means of gammagraphic images. This evaluation is made from positron images that require a second radiopharmaceutical application to the patient as well as the appropriate installation and instrumentation. ObjectiveTo evaluate the response to treatment in bone metastases due to castration-resistant prostate cancer patients treated with 223RaCl2 or 177Lu-iPSMA by estimating the uptake percentage and radiation absorbed dose in the metastatic lesion derived from gammagraphic images. MethodsTwo male patients with mCRCP received 4 and 3 cycles of 223RaCl2 and 177Lu-iPSMA, respectively. Lesion size evolution was assessed by absorbed dose calculated by MIRD methodology. Activity % was determined from gammagraphic images. ResultsTreatment with 223RaCl2 did not significantly reduce lesion size. However, the patient reported a significant reduction in pain. The patient treated with 177Lu-iPSMA showed a sustained reduction in lesion size. About 30% regression was achieved. ConclusionsThe proposed method avoids the additional use of positron radiopharmaceuticals and allows to correlate the response to treatment with the absorbed dose in the lesions.