Bone sarcomas may be induced throughout the skeleton (systemic) in mice by relatively low internal α-particle doses that are distributed over the whole skeleton. The induction of local (periosteal) bone sarcomas after paratibial deposition of insoluble radiocolloids required much higher doses, and in addition high energies of emitted particles. Paratibial deposition of α-particle-emitting radiocolloids of${}^{227}{\rm Th}$ and228 Th resulted in formation of both local and systemic bone sarcomas. The latter were most probably induced by the released radium daughters of the thorium isotopes and were distributed about the skeleton. Paratibial injections with β-particle emitters${}^{144}{\rm Ce}+{}^{144}{\rm Pr}$ (29 kBq per mouse) showed an incidence of local bone sarcomas of more than 80%. An estimation of the local effective doses led to values of more than 1000 Gy for the β-particle emitter${}^{144}{\rm Ce}$ and around 150 Gy for the thorium isotopes. Thus induction of local bone sarcomas required doses considerably greater than those needed for systemic bone sarcomas. The local induction of bone sarcomas has been reported for high-energy β particles using similar high doses of${}^{144}{\rm Ce}+{}^{144}{\rm Pr}$ in rats and for external${}^{90}{\rm Sr}+{}^{90}{\rm Y}$ irradiation in mice. We conclude that the processes involved in the induction of local and systemic bone sarcomas by radiation may be quite different.

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