Monte Carlo Treatment Planning, An Introduction

The accuracy of dose calculation engines used for treatment planning in radiotherapy has been increasing continuously, going from calculations based on measurements, to pencil beam algorithms and superposition/convolution algorithms. Currently Monte Carlo dose calculation engines are being implemented into commercial treatment planning software as it is believed that the Monte Carlo method can provide an accuracy within 2-3%. It is important that clinical physicists have an insight into these systems, when introducing them into the clinic. This report tackles this acute problem by providing an extensive information on: 

- General purpose Monte Carlo codes for photon and electron dosimetry applications
- Modelling of particle transport
- Cross sections
- MCTP (Monte Carlo Treatment Planning) specific issues such as linac modelling, CT conversion, variance reduction techniques, scoring grids - Recent developments such as 4D applications and MCTP optimization

An important question is: is the added value of MCTP clinically relevant? To answer this question an extensive literature overview is provided. The main conclusion is that the MC method has an important added value when compared to pencil beam algorithms. More information is needed when comparing MC to superposition/convolution algorithms, although the first experiments (comparing accurate Monte Carlo dose calculation engines to superposition/convolution algorithms) demonstrate that the MC method will become very important in clinical treatment planning.

As the Monte Carlo method is by its nature very time consuming, a number of approximations have been included in the commercial Monte Carlo dose calculation engines for treatment planning. This leads to a calculation time reduction of several orders of magnitude. The impact on the dosimetrical accuracy is not well known yet. This report provides an overview of the existing Monte Carlo dose calculation engines, focussing on the applied approximations. An overview of the commercial MCTP systems that are already available or are currently being developed is given. As benchmarking remains equally important as for any other treatment planning system, a paragraph is devoted to quality control. Commercial MCTP systems can be benchmarked by measurements but also by comparison with accurate Monte Carlo dose calculation engines containing few approximations.

https://doi.org/10.25030/ncs-016