title: Applicability of the linear-quadratic model to single and fractionated radiotherapy schedules: an experimental study.
abstract: The aim of this study was to examine the applicability of the linear-quadratic (LQ) model to single and fractionated irradiation in EMT6 cells. First, the α/β ratio of the cells was determined from single-dose experiments, and a biologically effective dose (BED) for 20 Gy in 10 fractions (fr) was calculated. Fractional doses yielding the same BED were calculated for 1-, 2-, 3-, 4-, 5-, 7-, 15- and 20-fraction irradiation using LQ formalism, and then irradiation with these schedules was actually given. Cell survival was determined by a standard colony assay. Differences in cell survival between pairs of groups were compared by t-test. The α/β ratio of the cells was 3.18 Gy, and 20 Gy in 10 fr corresponded to a BED3.18 of 32.6 Gy. The effects of 7-, 15- and 20-fraction irradiation with a BED3.18 of 32.6 Gy were similar to those of the 10-fraction irradiation, while the effects of 1- to 5-fraction irradiation were lower. In this cell line, the LQ model was considered applicable to 7- to 20-fraction irradiation or doses per fraction of 2.57 Gy or smaller. The LQ model might be applicable in the dose range below the α/β ratio.
authors.affiliation: Department of Radiology, Nagoya City University Graduate School of Medical Sciences, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya, Aichi 467-8601, Japan.
authors.forename: Akifumi
authors.initials: A
authors.lastname: Miyakawa
authors.forename: Yuta
authors.initials: Y
authors.lastname: Shibamoto
authors.forename: Shinya
authors.initials: S
authors.lastname: Otsuka
authors.forename: Hiromitsu
authors.initials: H
authors.lastname: Iwata
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000528:radiation effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000528:radiation effects; D003198:Computer Simulation; D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D016014:Linear Models; D051379:Mice; D008954:Models, Biological; D009374:Neoplasms, Experimental / Q000473:pathology / Q000503:physiopathology* / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D016896:Treatment Outcome
keywords: LQ model; biologically effective dose; hypofractionation; linear–quadratic model; stereotactic radiotherapy