Therapeutic and side effects of particle beam radiation in experimental animals

Human tumors are heterogeneous in various biological features including radiosensitivities. We here studied significance of tumor heterogeneity in relative biological effectiveness (RBE) of carbon ion therapy by using artificially mixed and transplanted experimental tumors in syngeneic mice. Sensitivity of three fibrosarcoma that we used for an experiment is as follows. Carbon ions: no.6107= no.8697> no.9037, Cs-137 γrays: no.6107 > no.8697> no.9037. We changed a combination and the mixture ratio of these sarcomas and prvided RBE. And we got the following conclusions. RBE of carbon ions depended on carbon-ion sensitivities but not γ-ray sensitivities of tumors. It was carbon-ion sensitive tumors but not resistant tumors that determine an RBE of a heterogeneous tumor. Feet of mice were locally irradiated with mono-peak carbon ions (290 MeV/u). Single doses and daily fractionation up to 6 fractions were used. Isoeffect doses were plotted against number of fractions for carbon ions. A linear regression line well fit to gamma-ray data in Fe-plot. However, this linearlity was gradually lost with an increase of linear energy transfer (LET) so that reciprocal isoeffect doses did not increase between single and 2 fractions for 58 keV/mm carbon ions. This means that sensitivity of skin cells for high LET carbon ions is different between single and fractionated doses. Prepared the new ridge filter by the data of the experiment of 18B157. And examine the biological effect by the new ridge filter. (author)