title: Biological microdosimetry based on radiation cytotoxicity data.
abstract: Researchers in the field of radiation microdosimetry have attempted to explain the relative biological effectiveness (RBE) of different ionising photon radiation sources on the basis of the singly stochastic, microdose metric lineal energy y, which only addresses physical stochasticity related to energy (ε) deposition via single events in the critical targets (cell nuclei assumed here). Biological stochasticity related to variable nuclei geometries and cell orientations (relative to the incoming radiation) is usually not addressed. Here a doubly stochastic microdose metric, the single-event hit size q (=ε/T), is introduced which allows the track length T to be stochastic. The new metric is used in a plausible model of metabolic-activity-based in vitro cytotoxicity of low-dose ionising photon radiation. The cytotoxicity model has parameters E{q} (average single-event hit size with q assumed to be exponentially distributed) and E{α}, which is the average value of the cellular response parameter α. E{α} is referred to as the biological signature and it is independent of q. Only E{q} is needed for determination of RBE. The model is used to obtain biological-microdosimetry-based q spectra for 320-kV X-rays and (137)Cs gamma rays and the related RBE for cytotoxicity. The spectra are similar to published lineal energy y spectra for 200-kV X-rays and (60)Co gamma rays for 1-μm biological targets.
authors.affiliation: Lovelace Respiratory Research Institute, Albuquerque, NM, USA. bscott@lrri.org
authors.forename: B R
authors.initials: BR
authors.lastname: Scott
authors.forename: J
authors.initials: J
authors.lastname: Hutt
authors.forename: Y
authors.initials: Y
authors.lastname: Lin
authors.forename: M T
authors.initials: MT
authors.lastname: Padilla
authors.forename: K M
authors.initials: KM
authors.lastname: Gott
authors.forename: C A
authors.initials: CA
authors.lastname: Potter
mesh_terms: D002467:Cell Nucleus / Q000528:radiation effects*; D002470:Cell Survival; D002478:Cells, Cultured; D002588:Cesium Radioisotopes / Q000032:analysis; D003037:Cobalt Radioisotopes / Q000032:analysis; D004307:Dose-Response Relationship, Radiation; D060733:Electromagnetic Radiation; D004847:Epithelial Cells / Q000528:radiation effects; D005720:Gamma Rays; D006801:Humans; D008962:Models, Theoretical; D017785:Photons; D011874:Radiometry / Q000379:methods*; D012062:Relative Biological Effectiveness; D013269:Stochastic Processes; D013778:Tetrazolium Salts / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D014965:X-Rays
chemical_list: D002588:Cesium Radioisotopes; D003037:Cobalt Radioisotopes; D013778:Tetrazolium Salts; D013844:Thiazoles; C022616:thiazolyl blue