Evaluation of plastic materials for range shifting, range compensation, and solid‐phantom dosimetry in carbon‐ion radiotherapy

Kanematsu, Nobuyuki; Koba, Yusuke; Ogata, Risa

doi:10.1118/1.4795338

Cited by 14 publications

(27 citation statements)

References 33 publications

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“…It has also been fully published in Medical Physics 41(7) 071704, July 2014 (http://dx.doi.org/10.1118/1.4870980 ). b) nkanemat@nirs.go.jp It was revealed recently that range shifting with PE would cause extra attenuation of carbon ions by 0.45%/cm as compared to water, 5 due to non water equivalence in nuclear interactions originated from compositional differences. In dosimetry, dose to water is often measured in non-water phantom with correction by fluence correction factor, which is a predetermined ratio of dose-in-water to dose-to-water in the phantom.…”

Section: -4mentioning

confidence: 99%

“…5 The secondary particles will increase inversely with reduction of the primary carbon ions. In the first-order approximation, secondaryparticle dose D 2 will thus increase with PE range shift s by the relative secondary-particle yield factor:…”

Section: Two-component Modelmentioning

confidence: 99%

“…In a group of clinical carbon-ion beams sharing the same ridge filter, D 1 /D 2 will vary with extraction energy or beam range due to attenuation of the primary carbon ions and yield of the secondary particles by nuclear interactions while ǫ 1 /ǫ 2 may be approximately invariant. Dose D 1 may decrease with the primary carbon ions that attenuate exponentially with attenuation length λ w = 25.5 cm in water, 5 and D 2 may increase just inversely in the first-order approximation. For a beam of range R, the dose ratio may thus be given by …”

Section: Energy Dependencementioning

confidence: 99%

“…5 We tested some of the clinical carbon-ion beams, in which 430-MeV beams were excluded as they have been only rarely used. The centralaxis doses for fields 10 cm in diameter were measured with special interest in the mid-to-distal part of the SOBP, with and without insertion of a 10-cm PE block in front of a dosimetric water phantom.…”

Section: Ridge-filter Design Datamentioning

confidence: 99%

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Influence of nuclear interactions in polyethylene range compensators for carbon-ion radiotherapy

Kanematsu¹,

Koba²,

Ogata³

et al. 2014

Med. Phys.

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Purpose: A recent study revealed that polyethylene (PE) would cause extra carbon-ion attenuation per range shift by 0.45%/cm due to compositional differences in nuclear interactions. The present study aims to assess the influence of PE range compensators on tumor dose in carbon-ion radiotherapy.Methods: Carbon-ion radiation was modeled to be composed of primary carbon ions and secondary particles, for each of which the dose and the relative biological effectiveness (RBE) were estimated at a tumor depth in the middle of spread-out Bragg peak. Assuming exponential behavior for attenuation and yield of these components with depth, the PE effect on dose was calculated for clinical carbon-ion beams and was partly tested by experiment. The two-component model was integrated into a treatment-planning system and the PE effect was estimated in two clinical cases. Results:The attenuation per range shift by PE was 0.1%-0.3%/cm in dose and 0.2%-0.4%/cm in RBEweighted dose, depending on energy and range-modulation width. This translates into reduction of RBEweighted dose by up to 3% in extreme cases. In the treatment-planning study, however, the effect on RBEweighted dose to tumor was typically within 1% reduction. Conclusions:The extra attenuation of primary carbon ions in PE was partly compensated by increased secondary particles for tumor dose. In practical situations, the PE range compensators would normally cause only marginal errors as compared to intrinsic uncertainties in treatment planning, patient setup, beam delivery, and clinical response.

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Section: -4mentioning

confidence: 99%

Section: Two-component Modelmentioning

confidence: 99%

Section: Energy Dependencementioning

confidence: 99%

Section: Ridge-filter Design Datamentioning

confidence: 99%

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Influence of nuclear interactions in polyethylene range compensators for carbon-ion radiotherapy

Kanematsu¹,

Koba²,

Ogata³

et al. 2014

Med. Phys.

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“…In order to select desirable materials for a range shifter, a thorough investigation of their effect on the pencil beam characteristics is necessary. One evaluation of various range shifter materials was reported by Kanematsu et al, 13 but in the context of carbon-ion radiotherapy.…”

Section: Introductionmentioning

confidence: 99%

Impact of range shifter material on proton pencil beam spot characteristics

et al. 2015

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Purpose: To quantitatively investigate the effect of range shifter materials on single-spot characteristics of a proton pencil beam. Methods: An analytic approximation for multiple Coulomb scattering ("differential Moliere" formula) was adopted to calculate spot sizes of proton spot scanning beams impinging on a range shifter. The calculations cover a range of delivery parameters: six range shifter materials (acrylonitrile butadiene styrene, Lexan, Lucite, polyethylene, polystyrene, and wax) and water as reference material, proton beam energies ranging from 75 to 200 MeV, range shifter thicknesses of 4.5 and 7.0 g/cm 2 , and range shifter positions from 5 to 50 cm. The analytic method was validated by comparing calculation results with the measurements reported in the literature. Results: Relative to a water-equivalent reference, the spot size distal to a wax or polyethylene range shifter is 15% smaller, while the spot size distal to a range shifter made of Lexan or Lucite is about 6% smaller. The relative spot size variations are nearly independent of beam energy and range shifter thickness and decrease with smaller air gaps. Conclusions: Among the six material investigated, wax and polyethylene are desirable range shifter materials when the spot size is kept small. Lexan and Lucite are the desirable range shifter materials when the scattering power is kept similar to water. C 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

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Design of a focused collimator for proton therapy spot scanning using Monte Carlo methods

et al. 2020

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Purpose: When designing a collimation system for pencil beam spot scanning proton therapy, a decision must be made whether or not to rotate, or focus, the collimator to match beamlet deflection as a function of off-axis distance. If the collimator is not focused, the beamlet shape and fluence will vary as a function of off-axis distance due to partial transmission through the collimator. In this work, we quantify the magnitude of these effects and propose a focused dynamic collimation system (DCS) for use in proton therapy spot scanning. Methods: This study was done in silico using a model of the Miami Cancer Institute's (MCI) IBA Proteus Plus system created in Geant4-based TOPAS. The DCS utilizes rectangular nickel trimmers mounted on rotating sliders that move in synchrony with the pencil beam to provide focused collimation at the edge of the target. Using a simplified setup of the DCS, simulations were performed at various off-axis locations corresponding to beam deflection angles ranging from 0°to 2.5°. At each offaxis location, focused (trimmer rotated) and unfocused (trimmer not rotated) simulations were performed. In all simulations, a 4 cm water equivalent thickness range shifter was placed upstream of the collimator, and a voxelized water phantom that scored dose was placed downstream, each with 4 cm airgaps. Results: Increasing the beam deflection angle for an unfocused trimmer caused the collimated edge of the beamlet profile to shift 0.08-0.61 mm from the baseline 0°simulation. There was also an increase in low-dose regions on the collimated edge ranging from 14.6% to 192.4%. Lastly, the maximum dose, D max , was 0-5% higher for the unfocused simulations. With a focused trimmer design, the profile shift and dose increases were all eliminated. Conclusions: We have shown that focusing a collimator in spot scanning proton therapy reduces dose at the collimated edge compared to conventional, unfocused collimation devices and presented a simple, mechanical design for achieving focusing for a range of source-to-collimator distances.

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Evaluation of plastic materials for range shifting, range compensation, and solid‐phantom dosimetry in carbon‐ion radiotherapy

Cited by 14 publications

References 33 publications

Influence of nuclear interactions in polyethylene range compensators for carbon-ion radiotherapy

Influence of nuclear interactions in polyethylene range compensators for carbon-ion radiotherapy

Impact of range shifter material on proton pencil beam spot characteristics

Design of a focused collimator for proton therapy spot scanning using Monte Carlo methods

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