Computational modeling of beam-customization devices for heavy-charged-particle radiotherap.pdf

a r X i v : 0 7 1 1 .4 1 7 8 v 2 [ p h y s i c s .m e d - p h ] 1 7 A p r 2 0 0 8 Submitted to: Phys. Med. Biol. Computational modeling of beam-customization devices for heavy-charged-particle radiotherapy Nobuyuki Kanematsu1,2, Shunsuke Yonai1, Azusa Ishizaki1,2 and Masami Torikoshi1 1 Department of Accelerator and Medical Physics, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan 2 Department of Quantum Science and Energy Engineering, Tohoku University, Aramaki-Aza-Aoba 01, Aoba-ku, Sendai 980-8579, Japan E-mail: nkanemat@nirs.go.jp Abstract. A model for beam customization with collimators and a range- compensating filter based on the phase-space theory for beam transport is presented for dose distribution calculation in treatment planning of radiotherapy with protons and heavier ions. Independent handling of pencil beams in conventional pencil-beam algorithms causes unphysical collimator- height dependence in the middle of large fields, which is resolved by the framework comprised of generation, transport, collimation, regeneration, range- compensation, and edge-sharpening processes with a matrix of pencil beams. The model was verified to be consistent with measurement and analytic estimation at a submillimeter level in penumbra of individual collimators with a combinational- collimated carbon-ion beam. The model computation is fast, accurate, and readily applicable to pencil-beam algorithms in treatment planning with capability of combinational collimation to make best use of the beam-customization devices. PACS numbers: 87.53.Mr, 87.53.Pb, 87.53.Uv 1. Introduction In heavy-charged-particle radiotherapy with protons and heavier ions, conventional broad-beam systems deliver variety of volumetrically enlarged standard beams and an optimum one of them is chosen and customized to an individual treatment target (Kanematsu et al 2007). The beam customization is usually made