Low-Dose Hypersensitivity in Chinese Hamster V79 Cells Targeted with Counted Protons Using a Charged-Particle Microbeam

Abstract

The Gray Laboratory charged-particle microbeam has been used to assess the clonogenic ability of Chinese hamster V79 cells after irradiation of their nuclei with a precisely defined number of protons with energies of 1.0 and 3.2 MeV. The microbeam uses a 1-microm silica capillary collimator to deliver protons to subcellular targets with high accuracy. The detection system is based on a miniature photomultiplier tube positioned above the cell dish, which detects the photons generated by the passage of the charged particles through an 18-microm-thick scintillator placed below the cells. With this system, a detection efficiency of greater than 99% is achieved. The cells are plated on specially designed dishes (3-microm-thick Mylar base), and the nuclei are identified by fluorescence microscopy. After an incubation period of 3 days, the cells are revisited individually to assess the formation of colonies from the surviving cells. For each energy investigated, the survival curve obtained for the microbeam shows a significant deviation below 1 Gy from a response extrapolated using the LQ model for the survival data above 1 Gy. The data are well fitted by a model that supports the hypothesis that radioresistance is induced by low-dose hypersensitivity. These studies demonstrate the potential of the microbeam for performing studies of the effects of single charged particles on cells in vitro. The hypersensitive responses observed are comparable with those reported by others using different radiations and techniques.

Low-Dose Hypersensitivity and Bystander Effect are Not Mutually Exclusive in A549 Lung Carcinoma Cells after Irradiation with Charged Particles

“…The tendency would be that cells show either HRS or BE, but both phenomena are mutually exclusive. However, it is worth noting that this study finds no bystander cell killing in a human glioblastoma which yet shows bystander micronuclei formation after a particles irradiation (Burdak-Rothkamm et al, 2006;Shao et al, 2005Shao et al, ,2003aShao et al, , 2004; also HRS has been detected in hamster cells (Schettino et al, 2001;Tsoulou et al, 2001), as well as the bystander effect for survival (Schettino et al, ,2003. Again, those experiments used different protocols, and looked at different endpoints, and therefore, conclusions are difficult.…”

“…Nevertheless, Schettino et al (2001) led some clonogenic assays on a hamster cell line and showed that most colonies contained between 75 cells and 85 cells, and that the proportion of those colonies decreased with dose. Therefore, Equation 2.3 is appropriate to measure the change in proliferation of cells occurring after radiation.…”

“…HRS is also seen after high-LET radiation (Bohrnsen et al, 2002;Schettino et aL, 2001;Tsoulou et al, 2001) but then IRR seems not to happen . Although found that HRS was independent of LET in hamster cells using 7r-mesons, Tsoulou et al (2001), using helium, found an increase in HRS with increasing LET.…”

Clinical consequences of relative biological effectiveness variations in proton radiotherapy of the prostate, brain and liver

“…In general, experimental data on proton RBE versus LET d (Folkard et al 1996, Belli et al 1989, 1993, Perris et al 1986, Coutrakon et al 1997, Wouters et al 1996, Schettino et al 2001 and proton RBE versus (α/β) x (Gerweck andKozin 1999, Paganetti et al 2000) indicate that RBE increases with increasing LET d (note that for protons the eventual decrease with LET d happens at LET d values irrelevant for clinical considerations) but decreases with increasing (α/β) x . The current data sets used to relate RBE with LET d and (α/β) x are subject to uncertainties (Carabe et al 2012, Carabe 2013).…”

“Broadbeam” irradiation of mammalian cells using a vertical microbeam facility

“…Similarly using a microbeam Schettino et al (2001), found low dose hypersensitivity with 3.2 MeV protons below 1 Gray, a result which cannot be observed with survival curves obtained with equivalent broadbeams. However, it was clear that a comparison above 1 Gy gave very similar results for both 1 and 3.2 MeV protons.…”