Bone pain palliation with 85Sr therapy

The aim of this retrospective study was to evaluate the efficacy of 85Sr in the palliation of metastatic bone pain. 85Sr decays by electron capture with a gamma emission of 514 keV and associated x-ray emissions of 10-15 keV; physical half-life is 64 d.

Between 1977 and 1992, 119 doses of 85Sr chloride (mean activity 335 MBq [9 mCi]) were intravenously administered to 108 patients with hyperalgic generalized bone metastases from prostatic carcinoma (52 patients), breast carcinoma (41) or other cancers (15). Pain, performance status, blood and urinary excretion values were investigated during follow-up, and survival time was recorded. Strontium bone scans were obtained up to 8 wk after injection to document isotope biodistribution and to estimate absorbed doses.

At 12 wk, 72.2% of patients showed significant benefit from treatment, i.e., enhanced quality of life and pain relief; 49.1% became free of pain. These beneficial effects lasted from 1 to 36 mo (mean 4.3 mo). The best symptomatic improvement was seen in patients treated at an early stage of metastatic skeletal disease and in prostate cancer patients. No evidence of a significant dose-response relationship was found in the data analysis. The mean absorbed dose ratio of metastases to marrow was estimated at 8.2. We found no evidence that hematological toxicity was a major problem; however, all patients experienced a reduction in blood counts, especially in platelets.

Systemic radionuclide therapy using 85Sr is a feasible, effective and well-tolerated palliative treatment in patients with refractory bone pain. We attained at least the same response rate as that reported with bone-seeking beta-emitting radionuclides such as 89Sr. The patients who benefited the most from 85Sr treatment were in an early stage of metastatic disease or had prostate cancer. Our clinical findings could not be linked to either the total injected activity of 85Sr or the estimated absorbed dose delivered to metastases.