Does Radioadaptive Response also Apply to the Case of Heavy-ion Irradiations in Fetal and Adult Mice? Part III. Priming Low Dose of Heavy-ion Irradiations Modifies Detrimental Effects from Challenging High Dose of Heavy-ion Irradiations.

Radiation-induced adaptive response (AR) is of great concern as studies on the conditions essential for AR induction provide important scientific basis for risk estimates, offer significant insight into the biological defense mechanisms, and lead to possible novel radiotherapy for practical application. At the 51st and 52nd JRRS annual meetings, induction of AR by 1) priming low dose of X-rays against high dose of high LET irradiations from accelerated heavy ions, and by 2) priming low dose of high LET irradiation from accelerated heavy ions against high dose of X-rays, were reported. In the present study, we tested 3) if AR could be induced in mice using high LET irradiations from accelerated heavy ions to delivery both the priming and the challenging doses. Accelerated heavy ion particles from mono beams of carbon, neon, silicon and iron generated by HIMAC, with the LET values of about 15, 30, 55, and 200 keV/micrometer respectively, are being examined. Results showed that priming low dose of carbon ion irradiations could induce AR against the high challenging dose from carbon ion irradiations, while no AR was observed when the challenging dose was from silicon or iron ion irradiations. No AR was observable for the combination of priming dose from neon ion irradiations and the challenging dose from carbon ion irradiations. These findings seemed to indicate that among the high LET irradiations from different ion species, only when the priming and challenging doses were delivered from irradiations with lower LET values, AR could be expected observable. Of course, induction of AR is resulted from a complicated interplay among multi-factors, and the possible effects from ion species could not be excluded yet. Of note, this is for the first time that AR is demonstrated by using high LET irradiations as both priming and challenging doses at the whole body level in a mouse AR model. The results obtained so far in this series of studies will be summarized for critical comments and discussion.