title: Model assembly for estimating cell surviving fraction for both targeted and nontargeted effects based on microdosimetric probability densities.
abstract: We here propose a new model assembly for estimating the surviving fraction of cells irradiated with various types of ionizing radiation, considering both targeted and nontargeted effects in the same framework. The probability densities of specific energies in two scales, which are the cell nucleus and its substructure called a domain, were employed as the physical index for characterizing the radiation fields. In the model assembly, our previously established double stochastic microdosimetric kinetic (DSMK) model was used to express the targeted effect, whereas a newly developed model was used to express the nontargeted effect. The radioresistance caused by overexpression of anti-apoptotic protein Bcl-2 known to frequently occur in human cancer was also considered by introducing the concept of the adaptive response in the DSMK model. The accuracy of the model assembly was examined by comparing the computationally and experimentally determined surviving fraction of Bcl-2 cells (Bcl-2 overexpressing HeLa cells) and Neo cells (neomycin resistant gene-expressing HeLa cells) irradiated with microbeam or broadbeam of energetic heavy ions, as well as the WI-38 normal human fibroblasts irradiated with X-ray microbeam. The model assembly reproduced very well the experimentally determined surviving fraction over a wide range of dose and linear energy transfer (LET) values. Our newly established model assembly will be worth being incorporated into treatment planning systems for heavy-ion therapy, brachytherapy, and boron neutron capture therapy, given critical roles of the frequent Bcl-2 overexpression and the nontargeted effect in estimating therapeutic outcomes and harmful effects of such advanced therapeutic modalities.
authors.affiliation: Research Group for Radiation Protection, Nuclear Science and Engineering Center, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki, Japan.
authors.forename: Tatsuhiko
authors.initials: T
authors.lastname: Sato
authors.affiliation: Radiation Safety Research Center, Nuclear Technology Research Laboratory, Central Research Institute of Electric Power Industry (CRIEPI), Komae, Tokyo, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Hamada
mesh_terms: D002460:Cell Line; D002470:Cell Survival; D006367:HeLa Cells; D006801:Humans; D008954:Models, Biological; D009369:Neoplasms / Q000235:genetics / Q000532:radiotherapy*; D011336:Probability; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics; D011882:Radiotherapy, High-Energy / Q000379:methods; D015854:Up-Regulation
chemical_list: D019253:Proto-Oncogene Proteins c-bcl-2