Tumoricidal activity of low-energy 160-KV versus 6-MV X-rays against platinum-sensitized F98 glioma cells

The purposes of this study were (i) to investigate the differences in effects between 160-kv low-energy and 6-mv high-energy x-rays,both by computational analysis and in vitro studies; (ii) to determine the effects of each on platinum-sensitized f98 rat glioma and murine b16 melanoma cells; and (iii) to describe the in vitro cytotoxicity and in vivo toxicity of a pt(ii) terpyridine platinum (typ-pt) complex. simulations were performed using the monte carlo code geant4 to determine enhancement in absorption of low- versus high-energy x-rays by pt and to determine dose enhancement factors (defs) for a pt-sensitized tumor phantom. in vitro studies were carried out using typ-pt and again with carboplatin due to the unexpected in vivo toxicity of typ-pt. cell survival was determined using clonogenic assays. in agreement with computations and simulations,in vitro data showed up to one log unit reduction in surviving fractions (sfs) of cells treated with 1-4 μg/ml of typ-pt and irradiated with 160-kv versus 6-mv x-rays. defs showed radiosensitization in the 50-200 kev range,which fell to approximate unity at higher energies,suggesting marginal interactions at mev energies. cells sensitized with 1-5 or 7 μg/ml of carboplatin and then irradiated also showed a significant decrease (p < 0.05) in sfs. however,it was unlikely this was due to increased interactions. theoretical and in vitro studies presented here demonstrated that the tumoricidal activity of low-energy x-rays was greater than that of high-energy x-rays against pt-sensitized tumor cells. determining whether radiosensitization is a function of increased interactions will require additional studies. © the author 2014. published by oxford university press on behalf of the japan radiation research society and japanese society for radiation oncology.