title: A new pencil beam model for photon dose calculations in heterogeneous media.
abstract: The pencil beam method is commonly used for dose calculations in intensity-modulated radiation therapy (IMRT). In this study, we have proposed a novel pencil model for calculating photon dose distributions in heterogeneous media. To avoid any oblique kernel-related bias and reduce computation time, dose distributions were computed in a spherical coordinate system based on the pencil kernels of different distances from source to surface (DSS). We employed two different dose calculation methods: the superposition method and the fast Fourier transform convolution (FFTC) method. In order to render the superposition method more accurate, we scaled the depth-directed component by moving the position of the entry point and altering the DSS value for a given beamlet. The lateral components were thus directly corrected by the density scaling method along the spherical shell without taking the densities from the previous layers into account. Significant computation time could be saved by performing the FFTC calculations on each spherical shell, disregarding density changes in the lateral direction. The proposed methods were tested on several phantoms, including lung- and bone-type heterogeneities. We compared them with Monte Carlo (MC) simulation for several field sizes with 6 MV photon beams. Our results revealed mean absolute deviations <1% for the proposed superposition method. Compared to the AAA algorithm, this method improved dose calculation accuracy by at least 0.3% in heterogeneous phantoms. The FFTC method was approximately 40 times faster than the superposition method. However, compared with MC, mean absolute deviations were <3% for the FFTC method.
authors: Laboratory of Image Science and Technology, Southeast University, Key Laboratory of Computer Network and Information Integration (Southeast University), Ministry of Education, Nanjing 210096, China; INSERM, U1099, F-35042 Rennes, France; Laboratoire Traitement du Signal et de l'Image, Universite de Rennes 1, F-35042 Rennes, France; Centre de Recherche en Information Médicale Sino-français (CRIBs), F-35042 Rennes, France.
authors: P
authors: P
authors: Zhang
authors: INSERM, U1099, F-35042 Rennes, France; Laboratoire Traitement du Signal et de l'Image, Universite de Rennes 1, F-35042 Rennes, France; Centre de Recherche en Information Médicale Sino-français (CRIBs), F-35042 Rennes, France.
authors: A
authors: A
authors: Simon
authors: INSERM, U1099, F-35042 Rennes, France; Laboratoire Traitement du Signal et de l'Image, Universite de Rennes 1, F-35042 Rennes, France; Centre de Recherche en Information Médicale Sino-français (CRIBs), F-35042 Rennes, France.
authors: R
authors: R
authors: De Crevoisier
authors: INSERM, U1099, F-35042 Rennes, France; Laboratoire Traitement du Signal et de l'Image, Universite de Rennes 1, F-35042 Rennes, France; Centre de Recherche en Information Médicale Sino-français (CRIBs), F-35042 Rennes, France.
authors: P
authors: P
authors: Haigron
authors: INSERM, U1099, F-35042 Rennes, France; Laboratoire Traitement du Signal et de l'Image, Universite de Rennes 1, F-35042 Rennes, France; Centre de Recherche en Information Médicale Sino-français (CRIBs), F-35042 Rennes, France.
authors: M H
authors: MH
authors: Nassef
authors: Shandong Tumor Hospital, Jinan 250117, China.
authors: B
authors: B
authors: Li
authors: Laboratory of Image Science and Technology, Southeast University, Key Laboratory of Computer Network and Information Integration (Southeast University), Ministry of Education, Nanjing 210096, China; Centre de Recherche en Information Médicale Sino-français (CRIBs), F-35042 Rennes, France. Electronic address: shu.list@seu.edu.cn.
authors: H
authors: H
authors: Shu
mesh_terms: D000465:Algorithms; D005583:Fourier Analysis; D008954:Models, Biological; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D017785:Photons / Q000627:therapeutic use*; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D013997:Time Factors
keywords: Dose calculations; FFTC; Superposition method