AN OVERVIEW OF MONTE CARLO TREATMENT

AN OVERVIEW OF MONTE CARLO TREATMENT

PLANNING FOR RADIOTHERAPY

Emiliano Spezi*and Geraint Lewis

Department of Medical Physics,Velindre Cancer Centre,Velindre Road,Whitchurch,

Cardiff CF142TL,Wales,UK

The implementation of Monte Carlo dose calculation algorithms in clinical radiotherapy treatment planning systems has been anticipated for many years.Despite a continuous increase of interest in Monte Carlo Treatment Planning (MCTP),its intro-duction into clinical practice has been delayed by the extent of calculation time required.The development of newer and faster MC codes is behind the commercialisation of the first MC-based treatment planning systems.The intended scope of this article is to provide the reader with a compact ‘primer’on different approaches to MCTP with particular attention to the latest developments in the field.

INTRODUCTION Recent statistics have shown that radiotherapy con-tributes to cure of 40%of cancer patients in the UK (1).However,radiotherapy represents only 5%of the total National Health Service expenditure in cancer care (2).Radiotherapy can therefore be con-sidered to be a clinically important and cost-effective form of cancer treatment.It has been shown that dose differences up to 7%can be clinically detectable and that deviations from the prescribed dose of 5%or more can compromise tumour response and tissue morbidity (3,4).The introduction into clinical practice of more accurate algorithms for patient dose calculation is therefore of paramount import-ance.Dose calculation algorithms based on the Monte Carlo (MC)method are widely regarded as the most accurate tool available in radiotherapy (5).A number of general-purpose MC codes are publicly available (e.g.FLUKA (6),MCNP (7),EGSnrc (8),Penelope (9),GEANT (10))and have been intensively used for research and development in medical appli-cations over the past decades.Recently,Rogers (11)reviewed techniques for electron–photon transport simulations with special emphasis on the EGS4/EGSnrc code system.Ma and Jiang (12)reviewed MC modelling techniques of clinical elec-tron beams,whereas Verhaegen and Seuntjens (13)focused their review on the modelling of external radiotherapy photon beams.Figure 1summarises the number of publications between 1985and 2007for general-purpose MC codes of major interest in medical physics ().Entries are grouped per scientific area.It is evident

that the MCNP code is used extensively in different

scientific fields.This is because of the flexibility and usability provided by the combinatorial geometry package and because of the possibility to transport all particles (i.e.neutrons,protons and heavy ions as

well as photons and electrons).However,in medi-cally related fields the EGS4/EGSnrc code system is very popular,representing a de facto standard for photon–electron transport in the energy range ( 1–10MeV)of radiotherapy interest.In particular,the number of publications reporting the use of MC in radiotherapy treatment planning (MCTP)has increased exponentially in the last 25years.This is clearly shown in Figure 2,where the number of MCTP scientific articles between 1985and 2007is sorted per year of publication.Despite a continuous increase of interest in MCTP ,the introduction of MC algorithms in clinical prac-

tice has been delayed by the excessive calculation

times involved.The development of newer and faster MC codes is behind the first wave of commercially

available MC-based treatment planning systems.Reynaert et al.(14)have recently discussed existing MC dose calculation ‘engines’and reported on specific issues regarding the commissioning of MCTP systems.Similarly Chetty et al.(5)have reviewed major MC codes being used in clinical applications and provided useful recommendations for the clinical implementation of MCTP .The intended scope of this article is to provide the reader with a compact ‘primer’on the different approaches to MCTP rather than an exhaustive review of the available MC codes and techniques,which have been already covered elsewhere.A BRIEF HISTOR Y OF MCTP

Several MC codes have been developed and used in

medical radiation physics in the past few decades.

Figure 3summarises the major release of popular MC codes used in radiotherapy physics,radiation *Corresponding author:emiliano.spezi@,espezi@ #The Author 2008.Published by Oxford University Press.All rights reserved.For Permissions,please email:journals.permissions@ Radiation Protection Dosimetry (2008),pp.1–7doi:10.1093/rpd /ncn277 Radiation Protection Dosimetry Advance Access published October 16, 2008 at Guangdong Medical College on December 28, 2010

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