title: Dynamic splitting of Gaussian pencil beams in heterogeneity-correction algorithms for radiotherapy with heavy charged particles.
abstract: The pencil-beam algorithm is valid only when elementary Gaussian beams are small enough compared to the lateral heterogeneity of a medium, which is not always true in actual radiotherapy with protons and ions. This work addresses a solution for the problem. We found approximate self-similarity of Gaussian distributions, with which Gaussian beams can split into narrower and deflecting daughter beams when their sizes have overreached lateral heterogeneity in the beam-transport calculation. The effectiveness was assessed in a carbon-ion beam experiment in the presence of steep range compensation, where the splitting calculation reproduced a detour effect amounting to about 10% in dose or as large as the lateral particle disequilibrium effect. The efficiency was analyzed in calculations for carbon-ion and proton radiations with a heterogeneous phantom model, where the beam splitting increased computing times by factors of 4.7 and 3.2. The present method generally improves the accuracy of the pencil-beam algorithm without severe inefficiency. It will therefore be useful for treatment planning and potentially other demanding applications.
authors.affiliation: Department of Accelerator and Medical Physics, National Institute of Radiological Sciences, Chiba 263-8555, Japan. nkanemat@nirs.go.jp
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Kanematsu
authors.forename: Masataka
authors.initials: M
authors.lastname: Komori
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Yonai
authors.forename: Azusa
authors.initials: A
authors.lastname: Ishizaki
mesh_terms: D000465:Algorithms; D002244:Carbon / Q000627:therapeutic use; D063193:Heavy Ion Radiotherapy; D008954:Models, Biological; D016011:Normal Distribution; D019047:Phantoms, Imaging; D061766:Proton Therapy; D011878:Radiotherapy / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted
chemical_list: D002244:Carbon