Lateral variations of radiobiological properties of therapeutic fields of 1H, 4He, 12C and 16O ions studied with Geant4 and microdosimetric kinetic model. (27th June 2017)

• Record Type: Journal Article
• Authors: Dewey, Sophie; Burigo, Lucas; Pshenichnov, Igor; Mishustin, Igor; Bleicher, Marcus
• Is Part Of: Physics in medicine & biology. Volume 62:Number 14(2017:Jul.)
• Page Start: 5884
• Page End: 5907
• Publication Date: 2017-06-27
• Subjects: theory and algorithms in physics of heavy-ion therapy -- Monte Carlo applications -- simulation -- microdosimetry -- RBE -- biological SOBP; Biophysics -- Periodicals; Medical physics -- Periodicals; 610.153
• DOI: 10.1088/1361-6560/aa75b2
• Languages: English
• ISSNs: 0031-9155

Abstract

Abstract: As known, in cancer therapy with ion beams the relative biological effectiveness (RBE) of ions changes in the course of their propagation in tissues. Such changes are caused not only by increasing the linear energy transfer (LET) of beam particles with the penetration depth towards the Bragg peak, but also by nuclear reactions induced by beam nuclei leading to the production of various secondary particles. Although the changes of RBE along the beam axis have been studied quite well, much less attention has been paid to the evolution of RBE in the transverse direction, perpendicular to the beam axis. In order to fill this gap, we simulated radiation fields of 1 H, 4 He, 12 C and 16 O nuclei of 20 mm in diameter by means of a Geant4-based Monte Carlo model for heavy-ion therapy connected with the modified microdosimetric kinetic model to describe the response of normal ( ( α / β ) x − r a y s = 3.8 Gy) and early-responding ( ( α / β ) x − r a y s = 10 Gy) tissues. Depth and radial distributions of saturation-corrected dose-mean lineal energy, RBE and RBE-weighted dose are investigated for passive beam shaping and active beam scanning. The field of 4 He has a small lateral spread as compared with 1 H field, and it is characterised by a modest lateral variation of RBE suggesting the use of fixed RBE values across the field transverse cross section at each depth. Reduced uncertainties of RBE on the boundary of a 4 He treatment field can be advantageous in a specific case of an organ at risk located in lateral proximity to the target volume. It is found that the lateral distributions of RBE calculated for 12 C and 16 O fields demonstrate fast variations in the radial direction due to changes of dose and composition of secondary fragments in the field penumbra. Nevertheless, the radiation fields of all four projectiles at radii larger than 20 mm can be characterized by a common RBE value defined by tissue radiosensitivity. These findings can help, in particular, in accessing the transverse homogeneity of radiation fields of ions used in studies in vitro .