Biological Response of Chinese Hamster B14-150 Cells to Sequential Combined Exposure to Protons and 12C Ions.

Proton and ion radiation therapy, when used both as single radiation and in mixed radiation mode, have a number of advantages over the conventional γ-therapy that are determined by physical characteristics of accelerated particles. The paper presents the results of an in vitro study of the effectiveness of sequential exposures of Chinese hamster tumor cells B14-150 to proton (p) and 12C ion beams. We used 4 irradiation schemes differing by the sequence of exposure and the contribution of each radiation to the total dose. Synergism was shown for 12C ions dose contribution of 45% (taking into account the coefficient of relative biological efficiency) and the sequence 12C→p.

Effects of Combined Exposure to Carbon Ions and Protons on the Pool of MCF-7 Breast Cancer Stem Cells In Vitro.

We studied the effects of single and combined action of protons and carbon ions 12C6+ on the pool of MCF-7 human breast cancer stem cells. Single irradiation with a beam of protons or carbon ions had no significant effects on the relative number of cancer stem cells (CSC). The effects of combined irradiation in a total equieffective dose of 4 Gy depended on the sequence of exposure to ionizing radiations: the relative number of CSC did not change after irradiation with carbon ions and then with protons, but increased in the case of the reverse sequence. The most favorable result, i.e. a decrease in the CSC pool, was observed in the case of sequential irradiation with carbon ions and protons and their equal contribution to total equieffective dose. In this case, the absolute number of CSC decreased by on average 2.1 times in comparison with the control (p<0.05). The revealed regularities are of interest for the further development of new methods of radiation therapy.

Post-Irradiation Recovery of B14-150 Fibrosarcoma Cells after Combined Irradiation with Low and High Linear Energy Transfer.

The use of radiation with low and high linear energy transfer (LET) in the same treatment regimen is promising in terms of increasing the efficiency and reducing the severity of radiation complications. Here we studied combined effect of protons (LET≈3 keV/µm) and heavy recoils (HR) induced by 14.5 MeV neutrons (LET≈290 keV/µm) on B14-150 fibrosarcoma cells. Comparison of the 4 irradiation schemes with different high-LET/low-LET dose ratios and the irradiation sequences revealed higher effectiveness of the combined action in the HR→protons sequence and with increasing HR dose contribution to 40% of the total dose. The observed effects were due to differences in the recovery of damages induced in cells by radiations with low and high LET.