Radiotoxicity after strontium-89 therapy for bone metastases using the micronucleus assay

The purpose of this study was to evaluate the degree of cytologic radiation damage to lymphocytes after Sr-89 therapy using the cytokinesis-blocked mi cronucleus assay. The chromosomal damage to lymphocytes exposed to Sr-89 in vivo should result in augmentation of the number of cells with micronucleu s. Methods: We studied eight patients with painful bone metastases, who wer e treated with 111 MBq Sr-89. Isolated lymphocytes collected from the patie nts 1 wk after therapy were harvested and treated according to the cytokine sis-blocked method of Fenech and Morley, The number of micronuclei per 500 binucleated cells was scored by visual inspection. As controls, lymphocytes from the same patients before therapy were also studied. For three patient s, serial blood samples were examined for a maximum of 2 mo after therapy. In an in vitro study, lymphocytes from five normal volunteers were exposed to doses varying from 0.25 to 1.0 Gy and studied with the same method. Resu lts: The mean number (+/-s.d.) of micronuclei per 500 binucleated cells aft er treatment was significantly increased (p < 0.05) as compared to control subjects (17.1 +/- 3.0 compared to 6.0 +/- 1.7). Thereafter, the number of micronuclei recovered gradually by 6 wk following therapy and, in one case, nearly to the baseline range in 2 mo. The number of micronuclei after 0.53 +/- 0.13 Gy of external irradiation was nearly equivalent to that after Sr -89 therapy. Conclusion: The relatively low frequency of lymphocyte micronu clei exposed to Sr-89 in vivo supported the contention that short-term nons tochastic damage with 111 MBq Sr-89 in patients with painful bone metastase s is minimal.