Validation of the physical and RBE-weighted dose estimator based on PHITS coupled with a microdosimetric kinetic model for proton therapy

Takada, Kunio; Sato, Tatsuhiko; Kumada, Hiroaki; Koketsu, Junichi; Takei, Hiroyuki; Sakurai, Hideyuki; Sakae, Takeji

doi:10.1093/jrr/rrx057

Cited by 46 publications

(41 citation statements)

References 44 publications

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“…Dose distributions with the VRBE naturally depend on the RBE calculation model. Although many researchers have also proposed RBE models [27] [28] [29], additional studies will be needed to accurately determine the dependence of RBE on various physical and biologic parameters [30] [31].…”

Section: Discussionmentioning

confidence: 99%

Biological Dose Comparison between a Fixed RBE and a Variable RBE in SFO and MFO IMPT with Various Multi-Beams for Brain Cancer

Kohno¹,

Cao²,

Bai³

et al. 2019

IJMPCERO

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IMPT plans with various multi-angle beams were planned by the Varian Eclipse treatment planning system for one case of brain cancer. Dose distributions for each plan, along with the associated linear energy transfer distributions, were recomputed using an in-house fast Monte Carlo dose calculator with a FRBE of 1.1 or with a previously published VRBE model. We then compared dosimetric parameters obtained by the VRBE with those obtained by the FRBE. Biological doses obtained by the VRBE for the clinical target volume in all plans were 1%-2% larger than those obtained by the FRBE. The minimum dose obtained by the VRBE for the right optic nerve in the MFO IMPT with 4 fields was 70% larger than that obtained by the FRBE, but the difference was only 18.1 cGy (RBE). The difference in maximum dose for the right optic nerve in the MFO IMPT with 5 fields was less than 10.4%, but the difference was 131.8 cGy (RBE). The mean difference in maximum dose was less than 2% for all other organs at risk. We found that biological dose with the FRBE had any dose errors in IMPT with various multi-angle beams.

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Section: Discussionmentioning

confidence: 99%

Biological Dose Comparison between a Fixed RBE and a Variable RBE in SFO and MFO IMPT with Various Multi-Beams for Brain Cancer

Kohno¹,

Cao²,

Bai³

et al. 2019

IJMPCERO

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“…Depending on the photon beam quality, the characteristics of the scattered radiation produced by the collimation system or inside the patient would change; consequently, the biological effect of scattered photons within the organ at risk or normal tissue could be different. Development of a MC platform capable of estimating the RBE‐weighted dose has been described in several studies . On the basis of these research results and a patient dose evaluation system developed in a previous study, the present study can be extended to assess the physical and biological dose in a patient according to the photon beam quality.…”

Section: Discussionmentioning

confidence: 95%

Determining the energy spectrum of clinical linear accelerator using an optimized photon beam transmission protocol

Choi

Park

et al. 2019

Medical Physics

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Purpose: The complex beam delivery techniques for patient treatment using a clinical linear accelerator (linac) may result in variations in the photon spectra, which can lead to dosimetric differences in patients that cannot be accounted for by current treatment planning systems (TPSs). Therefore, precise knowledge of the fluence and energy spectrum (ES) of the therapeutic beam is very important. However, owing to the high energy and flux of the beam, the ES cannot be measured directly, and validation of the spectrum modeled in the TPS is difficult. The aim of this study is to develop an efficient beam transmission measurement procedure for accurately reconstructing the ES of a therapeutic x-ray beam generated by a clinical linac. Methods: The attenuation of a 6 MV photon beam from an Elekta Synergy Platform clinical linac through different thicknesses of graphite and lead was measured using an ion chamber. The response of the ion chamber as a function of photon energy was obtained using the Monte Carlo (MC) method in the Geant4 simulation code. Using the curves obtained in the photon beam transmission measurements and the ion chamber energy response, the ES was reconstructed using an iterative algorithm based on a mathematical model of the spectrum. To evaluate the accuracy of the spectrum reconstruction method, the reconstructed ES (ES recon ) was compared to that determined by the MC simulation (ES MC ). Results: The ion chamber model in the Geant4 simulation was well validated by comparing the ion chamber perturbation factors determined by the TRS-398 calibration protocol and EGSnrc; the differences were within 0.57%. The number of transmission measurements was optimized to 10 for efficient spectrum reconstruction according to the rate of increase in the spectrum reconstruction accuracy. The distribution of ES recon obtained using the measured transmission curves was clearly similar to the reference, ES MC , and the dose distributions in water calculated using ES recon and ES MC were similar within a 2% local difference. However, in a heterogeneous medium, the dose discrepancy between them was >5% when a complex beam delivery technique composed of 171 control points was used. Conclusions: The proposed measurement procedure required a total time of approximately 1 h to obtain and analyze 20 transmission measurements. In addition, it was confirmed that the transmission curve of high-Z materials influences the accuracy of spectrum reconstruction more than that of low-Z materials. A well-designed transmission measurement protocol suitable for clinical environments could be an essential tool for better dosimetric accuracy in patient treatment and for periodic verification of the beam quality.

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“…The MC simulations reproduced the PMRC's double scattered beamline using the Particle and Heavy Ion Transport Code System (PHITS) ver3.02 . In a previous study, for the PMRC beamline, the PDD of a 155 MeV proton beam was evaluated using Monte Carlo simulation, and the measured values were reproduced. In this study, Monte Carlo simulations were carried out by adapting that calculation system.…”

Section: Methodsmentioning

confidence: 99%

3D‐printable lung phantom for distal falloff verification of proton Bragg peak

Koketsu

Kumada

Takada

et al. 2019

J Applied Clin Med Phys

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In proton therapy, the Bragg peak of a proton beam reportedly deteriorates when passing though heterogeneous structures such as human lungs. Previous studies have used heterogeneous random voxel phantoms, in which soft tissues and air are randomly allotted to render the phantoms the same density as human lungs, for conducting Monte Carlo (MC) simulations. However, measurements of these phantoms are complicated owing to their difficult‐to‐manufacture shape. In the present study, we used Voronoi tessellation to design a phantom that can be manufactured, and prepared a Voronoi lung phantom for which both measurement and MC calculations are possible. Our aim was to evaluate the effectiveness of this phantom as a new lung phantom for investigating proton beam Bragg peak deterioration. For this purpose, we measured and calculated the percentage depth dose and the distal falloff widths (DFW) passing through the phantom. For the 155 MeV beam, the measured and calculated DFW values with the Voronoi lung phantom were 0.40 and 0.39 cm, respectively. For the 200 MeV beam, the measured and calculated DFW values with the Voronoi lung phantom were both 0.48 cm. Our results indicate that both the measurements and MC calculations exhibited high reproducibility with plastinated lung sample from human body in previous studies. We found that better results were obtained using the Voronoi lung phantom than using other previous phantoms. The designed phantom may contribute significantly to the improvement of measurement precision. This study suggests that the Voronoi lung phantom is useful for simulating the effects of the heterogeneous structure of lungs on proton beam deterioration.

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Validation of the physical and RBE-weighted dose estimator based on PHITS coupled with a microdosimetric kinetic model for proton therapy

Cited by 46 publications

References 44 publications

Biological Dose Comparison between a Fixed RBE and a Variable RBE in SFO and MFO IMPT with Various Multi-Beams for Brain Cancer

Biological Dose Comparison between a Fixed RBE and a Variable RBE in SFO and MFO IMPT with Various Multi-Beams for Brain Cancer

Determining the energy spectrum of clinical linear accelerator using an optimized photon beam transmission protocol

3D‐printable lung phantom for distal falloff verification of proton Bragg peak

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