[en] For a 70-kg man injected intravascularly with a typical 25 ml of Thorotrast (approximately 0.6μCi²³²Th), the dose-rate to the endosteum, 0-10 μm from bone surfaces, is estimated at roughly 16 rad/yr, of which 7 rad/yr is from ²²⁴Ra, ²²⁸Th, and ²²⁸Ra translocated from Thorotrast to calcified bone, and 9 rad/yr is from Thorotrast on bone surfaces and in red marrow. Additional dosimetric analyses are needed to refine these provisional estimates. For the induction of osteosarcomas in the Thorotrast patients, it is possible that the most important dose is from the ²²⁴Ra continually deposited on all bone surfaces, rather than from the focal aggregates of Thorotrast which irradiate fewer bone cells but kill with multiple α-particles a higher fraction of those cells that are irradiated. (author)