An analytical dose‐averaged <scp>LET</scp> calculation algorithm considering the off‐axis <scp>LET</scp> enhancement by secondary protons for spot‐scanning proton therapy

Hirayama, S.; Matsuura, Tetsuya; Ueda, Hideaki; Fujii, Yusuke; Fujii, Takeshi; Sugiyama, Takao; Miyamoto, Naoki; Shimizu, Satoru; Fujimoto, Rintaro; Umegaki, Kikuo; Shirato, Hiroki

doi:10.1002/mp.12991

Cited by 20 publications

(32 citation statements)

References 37 publications

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“…This causes the 1D method to overestimate LET d in the high dose region while underestimating LET d in low dose regions (see Figs. 2(b1)-2(c2) (with energies of 140.8 and 70.2 MeV) of Hirayama et al 25 to Fig. In contrast, our hybrid 3D method can simultaneously calculate accurate LET d distributions in both high-dose and low-dose regions.…”

Section: Discussionmentioning

confidence: 92%

“…Due to the strong correlation between LET and RBE, several groups have developed LET-guided optimization techniques 4,8,13,[19][20][21][22][23][24][25] that shift high LET toward the target volume and away from the OARs to reduce toxicity. The recently published TG-256 report 15 also suggested assessing the potential clinical consequences associated with variable RBE models and recommended LET-guided optimization in treatment planning systems (TPSs).…”

Section: Introductionmentioning

confidence: 99%

“…25,[30][31][32][33] Generally speaking, MC is considered more accurate than analytical methods, but MC involves much longer calculation times and most institutions to date rely on analytical methods. 25,[30][31][32][33] Generally speaking, MC is considered more accurate than analytical methods, but MC involves much longer calculation times and most institutions to date rely on analytical methods.…”

Section: Introductionmentioning

confidence: 99%

“…25,[30][31][32][33] Generally speaking, MC is considered more accurate than analytical methods, but MC involves much longer calculation times and most institutions to date rely on analytical methods. In order to overcome this drawback, Hirayama et al 25 introduced a dual-Gaussian LET calculation kernel, which models contributions from the primary and the halo components of the proton beam separately. In contrast, MC simulations show a significant increase in LET with lateral distance from the beam axis due to the higher proportion of low-energy halo particles.…”

Section: Introductionmentioning

confidence: 99%

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New Hybrid 3D Analytical Linear Energy Transfer (LET) Calculation Algorithm Based on the Pre-Calculated Data from Monte Carlo (MC) Simulations

Deng

Ding

Younkin

et al. 2019

International Journal of Radiation Oncology*Biology*Physics

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Purpose The dose‐averaged linear energy transfer (LETd) for intensity‐modulated proton therapy (IMPT) calculated by one‐dimensional (1D) analytical models deviates from more accurate but time‐consuming Monte Carlo (MC) simulations. We developed a fast hybrid three‐dimensional (3D) analytical LETd calculation that is more accurate than 1D analytical model. Methods We used the Geant4 MC code to generate 3D LETd distributions of monoenergetic proton beams in water for all energies and used a customized error function to fit the LETd lateral profiles at various depths to the MC simulation. The 3D LETd calculation kernel was a lookup table of these fitted coefficients, and LETd was determined directly from spot energies and voxel coordinates during analytical dose calculations. We validated our new method by comparing the calculated LETd distributions to MC results using 3D Gamma index analysis with 3%/2 mm criteria in 12 patient geometries. The significance of the improvement in Gamma index analysis passing rates over the 1D analytical model was determined using the Wilcoxon rank‐sum test. Results The passing rate of 3D Gamma analysis comparing LETd distributions from the hybrid 3D method and the 1D method to MC simulations was significantly improved from 94.0% ± 2.5% to 98.0% ± 1.0% (P = 0.0003). The typical time to calculate dose and LETd simultaneously using an Intel Xeon E5‐2680 2.50 GHz workstation was approximately 2.5 min. Conclusions Our new method significantly improved the LETd calculation accuracy compared to the 1D method while maintaining significantly shorter calculation time even comparing with the GPU‐based fast MC code.

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Section: Discussionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…25,[30][31][32][33] Generally speaking, MC is considered more accurate than analytical methods, but MC involves much longer calculation times and most institutions to date rely on analytical methods. In order to overcome this drawback, Hirayama et al 25 introduced a dual-Gaussian LET calculation kernel, which models contributions from the primary and the halo components of the proton beam separately. In contrast, MC simulations show a significant increase in LET with lateral distance from the beam axis due to the higher proportion of low-energy halo particles.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

New Hybrid 3D Analytical Linear Energy Transfer (LET) Calculation Algorithm Based on the Pre-Calculated Data from Monte Carlo (MC) Simulations

Deng

Ding

Younkin

et al. 2019

International Journal of Radiation Oncology*Biology*Physics

View full text Add to dashboard Cite

show abstract

“…There are two approaches to calculating LET distributions: Monte Carlo (MC) simulations and analytical methods . Generally speaking, MC is considered more accurate than analytical methods, but MC involves much longer calculation times and most institutions to date rely on analytical methods.…”

Section: Introductionmentioning

confidence: 99%

Hybrid 3D analytical linear energy transfer calculation algorithm based on precalculated data from Monte Carlo simulations

et al. 2019

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Physical and biological impacts of collimator‐scattered protons in spot‐scanning proton therapy

Ueno

Matsuura

Hirayama

et al. 2019

J Applied Clin Med Phys

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To improve the penumbra of low‐energy beams used in spot‐scanning proton therapy, various collimation systems have been proposed and used in clinics. In this paper, focused on patient‐specific brass collimators, the collimator‐scattered protons' physical and biological effects were investigated. The Geant4 Monte Carlo code was used to model the collimators mounted on the scanning nozzle of the Hokkaido University Hospital. A systematic survey was performed in water phantom with various‐sized rectangular targets; range (5–20 cm), spread‐out Bragg peak (SOBP) (5–10 cm), and field size (2 × 2–16 × 16 cm2). It revealed that both the range and SOBP dependences of the physical dose increase had similar trends to passive scattering methods, that is, it increased largely with the range and slightly with the SOBP. The physical impact was maximized at the surface (3%–22% for the tested geometries) and decreased with depth. In contrast, the field size (FS) dependence differed from that observed in passive scattering: the increase was high for both small and large FSs. This may be attributed to the different phase‐space shapes at the target boundary between the two dose delivery methods. Next, the biological impact was estimated based on the increase in dose‐averaged linear energy transfer (LETd) and relative biological effectiveness (RBE). The LETd of the collimator‐scattered protons were several keV/μm higher than that of unscattered ones; however, since this large increase was observed only at the positions receiving a small scattered dose, the overall LETd increase was negligible. As a consequence, the RBE increase did not exceed 0.05. Finally, the effects on patient geometries were estimated by testing two patient plans, and a negligible RBE increase (0.9% at most in the critical organs at surface) was observed in both cases. Therefore, the impact of collimator‐scattered protons is almost entirely attributed to the physical dose increase, while the RBE increase is negligible.

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An analytical dose‐averaged LET calculation algorithm considering the off‐axis LET enhancement by secondary protons for spot‐scanning proton therapy

Cited by 20 publications

References 37 publications

New Hybrid 3D Analytical Linear Energy Transfer (LET) Calculation Algorithm Based on the Pre-Calculated Data from Monte Carlo (MC) Simulations

New Hybrid 3D Analytical Linear Energy Transfer (LET) Calculation Algorithm Based on the Pre-Calculated Data from Monte Carlo (MC) Simulations

Hybrid 3D analytical linear energy transfer calculation algorithm based on precalculated data from Monte Carlo simulations

Physical and biological impacts of collimator‐scattered protons in spot‐scanning proton therapy

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