Derivation of electron and photon energy spectra from electron beam central axis depth dose curves

Abstract

A method for deriving the electron and photon energy spectra from electron beam central axis percentage depth dose (PDD) curves has been investigated. The PDD curves of 6, 12 and 20 MeV electron beams obtained from the Monte Carlo full phase space simulations of the Varian linear accelerator treatment head have been used to test the method. We have employed a 'random creep' algorithm to determine the energy spectra of electrons and photons in a clinical electron beam. The fitted electron and photon energy spectra have been compared with the corresponding spectra obtained from the Monte Carlo full phase space simulations. Our fitted energy spectra are in good agreement with the Monte Carlo simulated spectra in terms of peak location, peak width, amplitude and smoothness of the spectrum. In addition, the derived depth dose curves of head-generated photons agree well in both shape and amplitude with those calculated using the full phase space data. The central axis depth dose curves and dose profiles at various depths have been compared using an automated electron beam commissioning procedure. The comparison has demonstrated that our method is capable of deriving the energy spectra for the Varian accelerator electron beams investigated. We have implemented this method in the electron beam commissioning procedure for Monte Carlo electron beam dose calculations.

Tikhonov regularization modified as improved method for determining electron energy spectra from percentage depth dose curves data of broad beams

“…Differences between original PDD R50 and reconstructed PDDs R50 were lower than 0.1 mm, the best results got for Deng et al (2001).…”

Photon Energy Spectrum Reconstruction Based on Monte Carlo and Measured Percentage Depth Dose in Accurate Radiotherapy

“…Such function was used by Jun Deng to initialize his model to unfold the photon contamination of electron beam. 4) We then introduce Eq. (6) …”

“…Deng et al reported that a random creep algorithm based on Monte Carlo simulations can reconstruct the photon energy spectra for Varian medical linac. 4) Benjamin Armbruster et al developed a linear method to reconstruct *Corresponding author, E-mail: gli@ipp.ac.cn the photon energy spectra; 5) though their results have low accuracy, their method can obtain the continuous photon energy spectra. The low accuracy may be a result of the PDD curves lowly responding to the photon energy spectra, and the linearization may lead to larger errors.…”

Determinação de Espectros de Energia de Elétrons Clínicos a partir de Curvas de Porcentagem de Dose em Profundidade (PDP) utilizando o Método de Recozimento Simulado Clássico

“…Vários métodos [3][4][5][6][7]10 têm sido desenvolvidos a fim de extrair o espectro de elétrons da curva de PDP do eixo central, fazendo uso da equação (1), a causa de ser este um problema mal-posto 1,310 .…”

“…Existem pelo menos três abordagens para resolver este problema 3,4 : Algoritmos úteis para estabelecer a contribuição na dose dos fótons de freamento gerados no cabeçote do acelerador têm sido investigados 2,7,8 . A influência do espalhamento angular inicial no espectro de energia dos elétrons incidentes também tem sido reportada 2,9 .…”