title: The 'X model': a modified version of the competition theory.
abstract: In 1985, Edgren et al. proposed a modified version of the competition theory to explain the interaction of sensitizers and protectors with target molecules damaged by radiation, which was designated the 'X' model. This model incorporates concepts which have been considered previously, namely that a type of radiation damage exists which cannot be chemically repaired, and that cells may contain a naturally occurring sensitizer. The model leads to testable predictions, such as, e.g. the crossing of 'K curves' when the level of protection is varied. It can only be applied to the immediate effects of radiation, i.e. before enzymatic reactions play a part. The present paper is a summary of work carried out since 1985 to test the predictions of the 'X' model and an exposition of the related algebra.
authors.affiliation: Department of Tumor Biology II, Karolinska Institute Medical School, Stockholm, Sweden.
authors.forename: O C
authors.initials: OC
authors.lastname: Scott
authors.forename: L
authors.initials: L
authors.lastname: Révész
authors.forename: M
authors.initials: M
authors.lastname: Edgren
mesh_terms: D000818:Animals; D004347:Drug Interactions; D000860:Hypoxia / Q000503:physiopathology; D008962:Models, Theoretical; D009584:Nitrogen / Q000502:physiology; D010100:Oxygen / Q000494:pharmacology*; D011837:Radiation-Protective Agents / Q000494:pharmacology*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D013438:Sulfhydryl Compounds / Q000494:pharmacology*
chemical_list: D011837:Radiation-Protective Agents; D011838:Radiation-Sensitizing Agents; D013438:Sulfhydryl Compounds; D009584:Nitrogen; D010100:Oxygen