ARTICLE IN PRESS Radiation Physics and Chemistry 76 (2007) 643–686 Review Monte Carlo treatment planning for photon and electron beams N. Reynaert à , S.C. van der Marck, D.R. Schaart, W. Van der Zee, C. Van Vliet-Vroegindeweij, M. Tomsej, J. Jansen, B. Heijmen, M. Coghe, C. De Wagter Medical Physics Department, Gent University, Proeftuinstraat 86, 9000 Gent, Belgium Received 18 November 2005; accepted 30 May 2006 Abstract During the last few decades, accuracy in photon and electron radiotherapy has increased substantially. This is partly due to enhanced linear accelerator technology, providing more flexibility in field definition (e.g. the usage of computer- controlled dynamic multileaf collimators), which led to intensity modulated radiotherapy (IMRT). Important improvements have also been made in the treatment planning process, more specifically in the dose calculations. Originally, dose calculations relied heavily on analytic, semi-analytic and empirical algorithms. The more accurate convolution/superposition codes use pre-calculated Monte Carlo dose ‘‘kernels’’ partly accounting for tissue density heterogeneities. It is generally recognized that the Monte Carlo method is able to increase accuracy even further. Since the second half of the 1990s, several Monte Carlo dose engines for radiotherapy treatment planning have been introduced. To enable the use of a Monte Carlo treatment planning (MCTP) dose engine in clinical circumstances, approximations have been introduced to limit the calculation time. In this paper, the literature on MCTP is reviewed, focussing on patient modeling, approximations in linear accelerator modeling and variance reduction techniques. An overview of published comparisons between MC dose engines and conventional dose calculations is provided for phantom studies and clinical examples, evaluating the added value of MCTP in the clinic. An overview of existing Monte Carlo dose engines and commercial MCTP systems is presented and some specific issues concerning the commissioning of a MCTP system are discussed. r 2006 Elsevier Ltd. All rights reserved. Keywords: Radiotherapy treatment planning; Monte Carlo Contents 1. Introduction ................................................................... 644 1.1. Scope of this review ......................................................... 645 1.2. Rationale for routine Monte Carlo treatment planning................................. 645 1.2.1. Requirements on uncertainty in treatment planning ............................. 645 1.2.2. Why Monte Carlo treatment planning ...................................... 645 1.2.3. Phantom experiments .................................................. 646 www.elsevier.com/locate/radphyschem 0969-806X/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2006.05.015 à Corresponding author. Tel.: +32 9 2646648; fax: +32 9 2646696. E-mail address: nick.reynaert@ugent.be (N. Reynaert).