A patient‐specific aperture system with an energy absorber for spot scanning proton beams: Verification for clinical application

Yasui, Kohichiroh; Toshito, T.; Omachi, C.; Kibe, Y.; Hayashi, Kensuke; Shibata, Hiroki; Tanaka, Kenichiro; Nikawa, Eiki; Asai, Kumiko; Shimomura, Akira; Kinou, Hideto; Isoyama, Shigeru; Fujii, Yusuke; Takayanagi, T.; Hirayama, S.; Nagamine, Yoshihiko; Shibamoto, Yuta; Komori, Masataka; Mizoe, Jun Etsu

doi:10.1118/1.4935528

Cited by 28 publications

(39 citation statements)

References 38 publications

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“…The TPS with the triple Gaussian kernel model is being applied to patient treatment with the spot scanning technique at the Nagoya Proton Therapy Center. The verification of patient-specific quality assurance has been reported by Yasui et al 33 Two methods have been proposed for creating the dose kernel model. First, Pedroni et al 9 and Li et al 13 proposed how to use the measured data.…”

Section: Discussionmentioning

confidence: 99%

Evaluation of the influence of double and triple Gaussian proton kernel models on accuracy of dose calculations for spot scanning technique

et al. 2016

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The difference between the results obtained with the two types of studied kernel models was distinct in the high energy region. The accuracy of calculations with the double Gaussian kernel model varied with the field size and SOBP width because the accuracy of prediction with the double Gaussian model was insufficient at the low-dose bump. The evaluation was only qualitative under limited volumetric irradiation conditions. Further accumulation of measured data would be needed to quantitatively comprehend what influence the double and triple Gaussian kernel models had on the accuracy of dose calculations.

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Section: Discussionmentioning

confidence: 99%

Evaluation of the influence of double and triple Gaussian proton kernel models on accuracy of dose calculations for spot scanning technique

et al. 2016

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“…The beam collimation system used for the spot‐scanning beamline simulated in this study was an extrapolation of a short‐range applicator (SRA) investigated by Yasui et al and consisted of a 2‐ or 4‐cm thick brass collimator and a 4‐cm thick energy absorber made of acrylonitrile–butadiene–styrene (ABS) plastic (Fig. ).…”

Section: Methodsmentioning

confidence: 99%

“…However, when shallow tumors are involved, the large spot size of the low‐energy proton beam resulting from the large‐angle Coulomb scattering might offset the dose conformity advantage gained by the scanning approach . To overcome this problem, different collimators have been designed and increasingly used in the clinics and their clinical benefits have been investigated in various studies, with positive results …”

Section: Introductionmentioning

confidence: 99%

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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“…The synchrotron can produce 95 proton beams energies having water penetration distances from 40 to 306 mm. The maximum spot size (1 σ ) in air at the isocenter plane is 13.8 mm, and the minimum is 4.7 mm . To irradiate shallow regions less than 40 mm, we used the energy absorber that had 40 mm water equivalent thickness.…”

Section: Methodsmentioning

confidence: 99%

Dosimetric verification of IMPT using a commercial heterogeneous phantom

Yasui

Toshito

Omachi

et al. 2019

J Applied Clin Med Phys

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The purpose of this study was to propose a verification method and results of intensity‐modulated proton therapy (IMPT), using a commercially available heterogeneous phantom. We used a simple simulated head and neck and prostate phantom. An ionization chamber and radiochromic film were used for measurements of absolute dose and relative dose distribution. The measured doses were compared with calculated doses using a treatment planning system. We defined the uncertainty of the measurement point of the ionization chamber due to the effective point of the chamber and mechanical setup error as 2 mm and estimated the dose variation base on a 2 mm error. We prepared a HU‐relative stopping power conversion table and fluence correction factor that were specific to the heterogeneous phantom. The fluence correction factor was determined as a function of depth and was obtained from the ratio of the doses in water and in the phantom at the same effective depths. In the simulated prostate plan, composite doses of measurements and calculations agreed within ±1.3% and the maximum local dose differences of each field were 10.0%. Composite doses in the simulated head and neck plan agreed within 4.0% and the maximum local dose difference for each field was 12.0%. The dose difference for each field came within 2% when taking the measurement uncertainty into consideration. In the composite plan, the maximum dose uncertainty was estimated as 4.0% in the simulated prostate plan and 5.8% in the simulated head and neck plan. Film measurements showed good agreement, with more than 92.5% of points passing a gamma value (3%/3 mm). From these results, the heterogeneous phantom should be useful for verification of IMPT by using a phantom‐specific HU‐relative stopping power conversion, fluence correction factor, and dose error estimation due to the effective point of the chamber.

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A patient‐specific aperture system with an energy absorber for spot scanning proton beams: Verification for clinical application

Abstract: The patient-specific aperture system improved dose distributions, particularly in shallow-region plans.

Cited by 28 publications

References 38 publications

Evaluation of the influence of double and triple Gaussian proton kernel models on accuracy of dose calculations for spot scanning technique

Evaluation of the influence of double and triple Gaussian proton kernel models on accuracy of dose calculations for spot scanning technique

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

Dosimetric verification of IMPT using a commercial heterogeneous phantom

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