Improved dose-calculation accuracy in proton treatment planning using a simplified Monte Carlo method verified with three-dimensional measurements in an anthropomorphic phantom

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Full Monte Carlo (FMC) calculation of dose distribution has been recognized to have superior accuracy, compared with the pencil beam algorithm (PBA). However, since the FMC methods require long calculation time, it is difficult to apply them to routine treatment planning at present. In order to improve the situation, a simplified Monte Carlo (SMC) method has been introduced to the dose kernel calculation applicable to dose optimization procedure for the proton pencil beam scanning. We have evaluated accuracy of the SMC calculation by comparing a result of the dose kernel calculation using the SMC method with that using the FMC method in an inhomogeneous phantom. The dose distribution obtained by the SMC method was in good agreement with that obtained by the FMC method. To assess the usefulness of SMC calculation in clinical situations, we have compared results of the dose calculation using the SMC with those using the PBA method for three clinical cases of tumor treatment. The dose distributions calculated with the PBA dose kernels appear to be homogeneous in the planning target volumes (PTVs). In practice, the dose distributions calculated with the SMC dose kernels with the spot weights optimized with the PBA method show largely inhomogeneous dose distributions in the PTVs, while those with the spot weights optimized with the SMC method have moderately homogeneous distributions in the PTVs. Calculation using the SMC method is faster than that using the GEANT4 by three orders of magnitude. In addition, the graphic processing unit (GPU) boosts the calculation speed by 13 times for the treatment planning using the SMC method. Thence, the SMC method will be applicable to routine clinical treatment planning for reproduction of the complex dose distribution more accurately than the PBA method in a reasonably short time by use of the GPU‐based calculation engine.PACS number(s): 87.55.Gh

Section: Methodsmentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Application of dose kernel calculation using a simplified Monte Carlo method to treatment plan for scanned proton beams

Mizutani

Takada

Kohno

et al. 2016

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“…For DMU calc,PSD and DMU calc,BSD calculations, we used the simplified Monte Carlo method (SMC) 12 , 13 . It tracks individual protons in a range compensator, an aperture collimator, and a phantom by calculating the range loss and scattering in materials using the water‐equivalent model (16) and the Highlands's equation.…”

Section: Methodsmentioning

confidence: 99%

“…However, since it takes much time to calculate the DMU with the full Monte Carlo method, reduction of calculation time is required to apply the Monte Carlo method for calculating the DMU in a patient routinely. Meanwhile, we have already developed a simplified Monte Carlo (SMC) method, with which we can quickly calculate dose distributions accurately 12 , 13 …”

Section: Introductionmentioning

confidence: 99%

Evaluation of monitor unit calculation based on measurement and calculation with a simplified Monte Carlo method for passive beam delivery system in proton beam therapy

Hotta

Kohno

Nagafuchi

et al. 2015

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Calibrating the dose per monitor unit (DMU) for individual patients is important to deliver the prescribed dose in radiation therapy. We have developed a DMU calculation method combining measurement data and calculation with a simplified Monte Carlo method for the double scattering system in proton beam therapy at the National Cancer Center Hospital East in Japan. The DMU calculation method determines the clinical DMU by the multiplication of three factors: a beam spreading device factor FBSD, a patient‐specific device factor FPSD, and a field‐size correction factor normalFFSfalse(Afalse). We compared the calculated and the measured DMU for 75 dose fields in clinical cases. The calculated DMUs were in agreement with measurements in ±1.1% for all of 25 fields in prostate cancer cases, and in ±3% for 94% of 50 fields in head and neck (H&N) and lung cancer cases, including irregular shape fields and small fields. Although the FBSD in the DMU calculations is dominant as expected, we found that the patient‐specific device factor and field‐size correction also contribute significantly to the calculated DMU. This DMU calculation method will be able to substitute the conventional DMU measurement for the majority of clinical cases with a reasonable calculation time required for clinical use.PACS number: 87.55.kh

A simplified Monte Carlo algorithm considering large‐angle scattering for fast and accurate calculation of proton dose

Takayanagi

Hirayama

Fujitaka

et al. 2017

PurposeThe purpose of this study is to improve dose calculation accuracy of the simplified Monte Carlo (SMC) algorithm in the low‐dose region. Because conventional SMC algorithms calculate particle scattering in consideration of multiple Coulomb scattering (MCS) only, they approximate lateral dose profiles by a single Gaussian function. However, it is well known that the low‐dose region spreads away from the beam axis, and it has been pointed out that modeling of the low‐dose region is important to calculated dose accurately.MethodsA SMC algorithm, which is named modified SMC and considers not only MCS but also large angle scattering resembling hadron elastic scattering, was developed. In the modified SMC algorithm, the particle fluence varies in the longitudinal direction because the large‐angle scattering decreases residual range of particles in accordance with their scattering angle and tracking of the particles with large scattering angle is terminated at a short distance downstream from the scattering. Therefore, modified integrated depth dose (m‐IDD) tables, which are converted from measured IDD in consideration of the fluence loss, are used to calculate dose.ResultsIn the case of a 1‐liter cubic target, the calculation accuracy was improved in comparison with that of a conventional algorithm, and the modified algorithm results agreed well with Geant4‐based simulation results; namely, 98.8% of the points satisfied the 2% dose/2 mm distance‐to‐agreement (DTA) criterion. The calculation time of the modified SMC algorithm was 1972 s in the case of 4.4 × 108 particles and 16‐threading operation of an Intel Xeon E5‐2643 (3.3‐GHz clock).ConclusionsAn SMC algorithm that can reproduce a laterally widespread low‐dose region was developed. According to the comparison with a Geant4‐based simulation, it was concluded that the modified SMC algorithm is useful for calculating dose of proton radiotherapy.