Establishing schedules for repeated doses of strontium and for concurrent chemotherapy in hormone-resistant patients with prostate cancer: measurement of blood and urine strontium levels.

Strontium-89 (Sr-89) alone or with concurrent chemotherapy has a role in the treatment of patients with prostate cancer (PCP). The schedules for repeated doses of Sr-89 or for concurrent chemotherapy is undetermined. The objective of this study was to measure the effective half-life (Te) of Sr-89 using a detector available in a nuclear research facility. Blood and urine samples obtained from PCP treated with Sr-89 (Metastron, Amersham, U.K.) were measured for radioactivity with a High Pure Germanium (HPGe) detector in a gamma spectrometry system (Eurisys, France). Twenty-five urine and 22 blood samples were obtained from 8 patients during a period of 160 days after Metastron injection. Sr-89 radioactivity levels in blood and urine were quite low (<8.2 x 10(-3) microCi/mL) in all patients after 21 days, whereas Sr-85 (available in 0.5% of Metastron) urine and, to a lesser extent, blood radioactivity levels were moderately high and could be detected up to 160 days. Based on Sr-85 urine levels, the calculated Sr-89 Te ranged from 9.6 to 20.7 days. Sr-89 Te can be routinely calculated in PCP based on HPGe detection of Sr-85 radioactivity levels in urine. This measurement can establish schedules for either repeated doses of Sr-89 or concurrent chemotherapy.