title: Radiobiological effectiveness (RBE) of megavoltage X-ray and electron beams in radiotherapy.
abstract: Recent experiments indicate that significant differences exist in the microdosimetric properties (i.e., lineal energy distributions) of megavoltage X-ray and electron beams used in radiation therapy. In particular, dose averaged values of lineal energy for 18 MeV electrons are 10-30% lower than for 10 MeV bremsstrahlung X rays, which in turn are 30-60% lower than for 250 kVp X rays. Differences of this magnitude may manifest themselves in observable radiobiological effectiveness (RBE) differences between these radiations. Cell survival data have been obtained for line DLD-1 human tumor cells on all three of the above radiation sources. Results clearly demonstrate an RBE difference between orthovoltage and megavoltage radiation (P = 0.001). A small difference is also measured in RBE between megavoltage photons and megavoltage electrons, but the difference is not statistically significant (P = 0.25). All biological, dosimetric, and microdosimetric data were obtained under nearly identical geometric conditions. These data raise interesting questions vis à vis the applicability of microdosimetric theories in the interpretation of biological effects.
authors.forename: H I
authors.initials: HI
authors.lastname: Amols
authors.forename: B
authors.initials: B
authors.lastname: Lagueux
authors.forename: D
authors.initials: D
authors.lastname: Cagna
mesh_terms: D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects; D003110:Colonic Neoplasms / Q000473:pathology; D004307:Dose-Response Relationship, Radiation; D004583:Electrons; D006801:Humans; D010315:Particle Accelerators; D011882:Radiotherapy, High-Energy; D012062:Relative Biological Effectiveness; D014965:X-Rays