HPRT1 and glioblastoma: The inverse dose rate phenomenon has been demonstrated for different exposure conditions and biological end points, for instance for mutation induction in human lymphoblasts in response to 137Cs γ-rays [32], deletions size in the HPRT locus in human lymphoblastoid cells following 200 keV X-ray exposure [33], micronuclei induction in Lewis lung carcinoma cells exposed to 60Co γ-rays [34], and cytokine gene expression in human glioblastoma cell lines irradiated with 137Cs γ-rays [35].