BACKGROUND AND PURPOSE: The reaction of human tumor cells and mammalian normal tissue to irradiation with low energy protons and X-rays was examined. MATERIAL AND METHODS: An irradiation facility with a vertical proton beam was set up at the Tandem accelerator at the University of Erlangen. U-138MG human glioblastoma cells and B14 hamster fibroblasts were irradiated with 5.7 and 7.0 MeV protons (LET 7.27 and 6.23 keV/microm) and with 120 kV X-rays. The inactivation was measured by the colony forming assay, induction and repair of DNA double strand breaks (DSB) by constant field gel electrophoresis and cell cycle control by image cytometry. RESULTS: An obvious reduction of the shoulder of the dose effect curve was determined. This effect was more pronounced for the glioblastoma cell line. The RBE at 10% survival was measured as 1.78 +/- 0.09 for glioblastoma cells and 1.18 +/- 0.06 for B14 fibroblasts. The induction of DNA DSB in glioblastoma cells showed an RBE of 0.96 +/- 0.06, after 24h repair time an RBE of 2.63 +/- 0.07 was calculated. Protons had a larger and enduring effect on G2 arrest of cell cycle than X-rays, 72 hours after irradiation with 10 Gy an RBE of 1.57 +/- 0.05 was calculated. CONCLUSIONS: The effect of higher LET irradiation was more distinct for tumor cells than for normal tissue. Both cell lines showed a higher RBE for cell survival than the value of 1.1 normally used for proton therapy. Repair capacity of DNA DSB was reduced following low energy proton irradiation and G2 arrest was induced to a larger degree. Further experiments are needed to elucidate if this could be a reason for lower cell survival.
BACKGROUND AND PURPOSE: The reaction of humantumor cells and mammalian normal tissue to irradiation with low energy protons and X-rays was examined. MATERIAL AND METHODS: An irradiation facility with a vertical proton beam was set up at the Tandem accelerator at the University of Erlangen. U-138MG humanglioblastoma cells and B14hamster fibroblasts were irradiated with 5.7 and 7.0 MeV protons (LET 7.27 and 6.23 keV/microm) and with 120 kV X-rays. The inactivation was measured by the colony forming assay, induction and repair of DNA double strand breaks (DSB) by constant field gel electrophoresis and cell cycle control by image cytometry. RESULTS: An obvious reduction of the shoulder of the dose effect curve was determined. This effect was more pronounced for the glioblastoma cell line. The RBE at 10% survival was measured as 1.78 +/- 0.09 for glioblastoma cells and 1.18 +/- 0.06 for B14 fibroblasts. The induction of DNA DSB in glioblastoma cells showed an RBE of 0.96 +/- 0.06, after 24h repair time an RBE of 2.63 +/- 0.07 was calculated. Protons had a larger and enduring effect on G2 arrest of cell cycle than X-rays, 72 hours after irradiation with 10 Gy an RBE of 1.57 +/- 0.05 was calculated. CONCLUSIONS: The effect of higher LET irradiation was more distinct for tumor cells than for normal tissue. Both cell lines showed a higher RBE for cell survival than the value of 1.1 normally used for proton therapy. Repair capacity of DNA DSB was reduced following low energy proton irradiation and G2 arrest was induced to a larger degree. Further experiments are needed to elucidate if this could be a reason for lower cell survival.
Authors: Laura Vanderwaeren; Rüveyda Dok; Karin Voordeckers; Laura Vandemaele; Kevin J Verstrepen; Sandra Nuyts Journal: Int J Mol Sci Date: 2022-05-14 Impact factor: 6.208