- 30 - t The work of Laskin, et al, though not specifically "involving deep respiratory tissue, does demonstrate a source intensity-response curve for lung tissue’?, A Ru-106 ° cylindrical source was implanted in the bronchi of rats, and cancers were observed to arise from the bronchial epithelium. _ The response curve indicates a substantial response (7 percent) _ even at 0.008 uCi burden, and a slow, approximately logarithmic _increase of tumor incidence over three orders of magnitude. in the source intensity. Corresponding first-year doses to adjacent bronehial epithelium varied from 103 rad to 106 rad’, _Animals were followed until death and it was observed that the tumor incidence generally increased with the dose accumulated at death. The lowest accumulated dose associated with a cancer was 1400 rad. For an accumulated dose of the order of 106 rad the incidence was approximately two-thirds. -_— Cember —~— ._ fortified glass beads (0.3 u diameter) with several microcuries of Sr-90, and single beads were implanted in the lungs of rats. Tumors were observed in 7 of 23 animals. In a second _@xperiment Cember exposed rat lungs to Ce-144 particles. For 49/ Laskin, S., M. Kuschner, N. Nelson, B. Altshuler, J.4. Hariecy and M. Daniels, "Carcinoma of the lung in rats éxpcsed to the beta-radiation of intra-bronchial rutheniuml96 pelicts “it. Dose response relationshivus,” J. 1963, pp. 219-231. Natl. Cancer Inst. si, “SO0/ Altshuler, B., "Dosimetry fror a rnut96-coateod mlatinum pellet," Radiation Res. 9, 1958, pp. 626-632. rN hw