A phase space model of a Versa HD linear accelerator for application to Monte Carlo dose calculation in a real‐time adaptive workflow

Bedford, James L.; Nilawar, Rahul; Nill, Simeon; Oelfke, Uwe

doi:10.1002/acm2.13663

Cited by 4 publications

(5 citation statements)

References 48 publications

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“…It should be emphasised that the accuracy of every advanced dose calculation algorithm depends on an accurate representation of the particle fluence from the accelerator. For the case of photons, an evaluation of the source model used in this work has been carried out previously (Bedford et al 2022 ). With regard to the LBTE solver itself, there are some limitations as it is currently implemented.…”

Section: Discussionmentioning

confidence: 99%

“…A 6 MV flattened beam was considered in this work, although the approach can also be used for a flattening filter-free beam. For each of the two radiation sources in the dual-source model, representing primary photons and head scatter, divergent rays were traced throughout the patient model according to a regular Cartesian grid defined at the isocentric plane (Siddon 1985 , Bedford et al 2022 ). The intensities of the rays were determined from the off-axis position of the rays according to a lookup table defined in the beam data for the dose calculation model (Bedford 2002 ).…”

Section: Methodsmentioning

confidence: 99%

“…For the Versa HD accelerator, the primary source was modelled as having a width (standard deviation) of 0.8 mm and a length of 1.0 mm, while the secondary source, at 150 mm from the primary source, was modelled as having a width and length of 18.0 mm. Further details of the source model are given elsewhere (Bedford et al 2022 ).…”

Section: Methodsmentioning

confidence: 99%

“…The general performance of the LBTE algorithm was also assessed by comparing LBTE with Monte Carlo simulation for a prostate plan and a lung plan, both plans using photon IMRT. These plans were previously used for a comparison of tumour tracking technologies and the Monte Carlo dose distributions were also previously reported (Bedford et al 2022 ). Further details of the plans and the phase space model are given in that publication.…”

Section: Methodsmentioning

confidence: 99%

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A discrete ordinates Boltzmann solver for application to inverse planning of photons and protons

Bedford

2023

Phys. Med. Biol.

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The aim of this work is to develop a discrete ordinates Boltzmann solver that can be used for calculation of absorbed dose from both photons and protons within an inverse planning optimiser, so as to perform accurate dose calculation throughout the whole of the inverse planning process. With photons, five transport sweeps were performed to obtain scattered photon fluence, and unscattered electron fluence was then obtained and used as a fixed source for solution of the electron transport equations. With protons, continuous slowing down was treated as a fixed source, and five transport sweeps were used to calculate scattered fluence. The total electron or proton fluence was multiplied by the stopping power ratio for the transport medium to obtain absorbed dose. The method was evaluated in homogeneous media and in a lung case where the planning target volume was surrounded by low-density lung material. Photon arc, proton passive scattering and proton arc treatments were considered. The results were compared to a clinically validated convolution dose calculation for photons, and with an analytical method for protons. In water-equivalent media, the discrete ordinates method agrees with the alternative algorithms to within 2%. Convergence is found to be sufficiently complete for water-, lung- and bone-equivalent materials after five iterations. The dose calculated by the relatively simple angular quadrature is seen to be very close to that calculated by a more comprehensive quadrature. For inhomogeneous lung plans, the method shows more heterogeneity of dose to the planning target volume than the comparative methods. The discrete ordinates Boltzmann solver provides a general framework for dose calculation with both photons and protons. The method is suitable for incorporation into an inverse planning optimiser, so that accurate dose calculation in a heterogeneous medium can be obtained throughout inverse planning, with the result that the final dose distribution is as predicted by the optimiser.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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A discrete ordinates Boltzmann solver for application to inverse planning of photons and protons

Bedford

2023

Phys. Med. Biol.

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“…This study used a dual-source model of a Versa HD linear accelerator (Elekta AB, Stockholm) with a source-axis distance of 1000 mm (Bedford et al 2013(Bedford et al , 2022. A 6 MV flattened beam was considered in this work.…”

Section: Boltzmann Solvermentioning

confidence: 99%

Inverse planning of lung radiotherapy with photon and proton beams using a discrete ordinates Boltzmann solver

Bedford

2024

Phys. Med. Biol.

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Objective A discrete ordinates Boltzmann solver has recently been developed for use as a fast and accurate dose engine for calculation of photon and proton beams. The purpose of this study is to apply the algorithm to the inverse planning process for photons and protons and to evaluate the impact that this has on the quality of the final solution.Approach The method was implemented into an iterative least-squares inverse planning optimiser, with the Boltzmann solver used every 20 iterations over the total of 100 iterations. Elemental dose distributions for the intensity modulation and the dose changes at the intermediate iterations were calculated by a convolution algorithm for photons and a simple analytical model for protons. The method was evaluated for 12 patients in the heterogeneous tissue environment encountered in radiotherapy of lung tumours. Photon arc and proton arc treatments were considered in this study. The results were compared with those for use of the Boltzmann solver solely at the end of inverse planning or not at all.Main results Application of the Boltzmann solver at the end of inverse planning shows the dose heterogeneity in the planning target volume to be greater than calculated by convolution and empirical methods, with the median root-mean-square dose deviation increasing from 3.7 to 5.3 for photons and from 1.9 to 3.4 for proton arcs. Use of discrete ordinates throughout inverse planning enables homogeneity of target coverage to be maintained throughout, the median root-mean-square dose deviation being 3.6 for photons and 2.3 for protons. Dose to critical structures is similar with discrete ordinates and conventional methods. Time for inverse planning with discrete ordinates takes around 1-2 hours using a contemporary computing environment.Significance By incorporating the Boltzmann solver into an iterative least squares inverse planning optimiser, accurate dose calculation in a heterogeneous medium is obtained throughout inverse planning, with the result that the final dose distribution is of the highest quality.

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A phase space model of a Versa HD linear accelerator for application to Monte Carlo dose calculation in a real‐time adaptive workflow

Bedford

Nilawar

Nill

et al. 2022

J Applied Clin Med Phys

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This study aims to develop and validate a simple geometric model of the accelerator head, from which a particle phase space can be calculated for application to fast Monte Carlo dose calculation in real-time adaptive photon radiotherapy.With this objective in view,the study investigates whether the phase space model can facilitate dose calculations which are compatible with those of a commercial treatment planning system, for convenient interoperability. Materials and methods:A dual-source model of the head of a Versa HD accelerator (Elekta AB, Stockholm, Sweden) was created. The model used parameters chosen to be compatible with those of 6-MV flattened and 6-MV flattening filter-free photon beams in the RayStation treatment planning system (RaySearch Laboratories, Stockholm, Sweden). The phase space model was used to calculate a photon phase space for several treatment plans, and the resulting phase space was applied to the Dose Planning Method (DPM) Monte Carlo dose calculation algorithm. Simple fields and intensity-modulated radiation therapy (IMRT) treatment plans for prostate and lung were calculated for benchmarking purposes and compared with the convolution-superposition dose calculation within RayStation. Results: For simple square fields in a water phantom, the calculated dose distribution agrees to within ±2% with that from the commercial treatment planning system, except in the buildup region, where the DPM code does not model the electron contamination. For IMRT plans of prostate and lung, agreements of ±2% and ±6%, respectively, are found, with slightly larger differences in the high dose gradients. Conclusions:The phase space model presented allows convenient calculation of a phase space for application to Monte Carlo dose calculation, with straightforward translation of beam parameters from the RayStation beam model. This provides a basis on which to develop dose calculation in a real-time adaptive setting.

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A phase space model of a Versa HD linear accelerator for application to Monte Carlo dose calculation in a real‐time adaptive workflow

Cited by 4 publications

References 48 publications

A discrete ordinates Boltzmann solver for application to inverse planning of photons and protons

A discrete ordinates Boltzmann solver for application to inverse planning of photons and protons

Inverse planning of lung radiotherapy with photon and proton beams using a discrete ordinates Boltzmann solver

A phase space model of a Versa HD linear accelerator for application to Monte Carlo dose calculation in a real‐time adaptive workflow

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