title: An approximation of central-axis absorbed dose in narrow photon beams.
abstract: In narrow photon beams of therapeutic energy range, the absorbed dose derived from experimental measurements is subject to a significant error. The error stems from high dose gradients characteristic to small radiation fields and from finite probe dimensions. In this study, a simple model for the narrow-beam absorbed dose is described. It is shown that broad-beam dose data are sufficient to predict a narrow-beam dose. The dose is calculated as a sum of primary and scatter components given in the form of respective analytical functions. For both functions, numerical coefficients are determined in broad-beam geometry. The model is evaluated by comparing calculated dose values with the Monte Carlo simulated narrow-beam dose data for 6 and 15 MV x rays.
authors.affiliation: Baylor College of Medicine, Department of Radiology, Houston, Texas, USA. pnizin@bcm.tmc.edu
authors.forename: P S
authors.initials: PS
authors.lastname: Nizin
authors.forename: R B
authors.initials: RB
authors.lastname: Mooij
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D006801:Humans; D008962:Models, Theoretical; D009010:Monte Carlo Method; D017785:Photons / Q000627:therapeutic use*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D011882:Radiotherapy, High-Energy; D012542:Scattering, Radiation