Analysis of the track‐ and dose‐averaged LET and LET spectra in proton therapy using the <scp>geant</scp>4 Monte Carlo code

Guan, Fada; Peeler, C; Bronk, Lawrence F.; Geng, Changran; Taleei, Reza; Randeniya, S.; Ge, Shuaiping; Mirković, Dragan; Grosshans, David R.; Mohan, Radhe; Titt, Uwe

doi:10.1118/1.4932217

Cited by 111 publications

(112 citation statements)

References 70 publications

(78 reference statements)

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“…(1) for implementation into the simulation, LET was modeled for in Geant4 although an alternative approach would be to measure the LET values by averaging the collision energy deposited over a finite trajectory length as described by Guan et al.,29 along with the depth dose curve and measured scintillated light output. The current model neglects any ionization that comes from secondary particles.…”

Section: Methodsmentioning

confidence: 99%

Quality assurance in proton beam therapy using a plastic scintillator and a commercially available digital camera

Almurayshid

Helo

Kacperek

et al. 2017

J Applied Clin Med Phys

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PurposeIn this article, we evaluate a plastic scintillation detector system for quality assurance in proton therapy using a BC‐408 plastic scintillator, a commercial camera, and a computer.MethodsThe basic characteristics of the system were assessed in a series of proton irradiations. The reproducibility and response to changes of dose, dose‐rate, and proton energy were determined. Photographs of the scintillation light distributions were acquired, and compared with Geant4 Monte Carlo simulations and with depth‐dose curves measured with an ionization chamber. A quenching effect was observed at the Bragg peak of the 60 MeV proton beam where less light was produced than expected. We developed an approach using Birks equation to correct for this quenching. We simulated the linear energy transfer (LET) as a function of depth in Geant4 and found Birks constant by comparing the calculated LET and measured scintillation light distribution. We then used the derived value of Birks constant to correct the measured scintillation light distribution for quenching using Geant4.ResultsThe corrected light output from the scintillator increased linearly with dose. The system is stable and offers short‐term reproducibility to within 0.80%. No dose rate dependency was observed in this work.ConclusionsThis approach offers an effective way to correct for quenching, and could provide a method for rapid, convenient, routine quality assurance for clinical proton beams. Furthermore, the system has the advantage of providing 2D visualization of individual radiation fields, with potential application for quality assurance of complex, time‐varying fields.

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Section: Methodsmentioning

confidence: 99%

Quality assurance in proton beam therapy using a plastic scintillator and a commercially available digital camera

Almurayshid

Helo

Kacperek

et al. 2017

J Applied Clin Med Phys

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“…The MCNPX simulation provided dose and total fluence (the number of protons traversing an area) in each voxel, which were used to calculate the track-averaged LET (LET t ) [32]. Although most studies have been based on dose-averaged LET (LET d ), the LET t is an acceptable approximation for LET d for lower values of LET, such as those encountered in most treatment plans, because LET t is linearly proportional to LET d in this low-LET region [33]. Many of the treatment plans consisted of a primary plan and 1 or 2 boost plans.…”

Section: Methodsmentioning

confidence: 99%

Clinical evidence of variable proton biological effectiveness in pediatric patients treated for ependymoma

Peeler

Mirković

Titt

et al. 2016

Radiotherapy and Oncology

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Background and Purpose A constant relative biological effectiveness (RBE) is used for clinical proton therapy; however, experimental evidence indicates that RBE can vary. We analyzed pediatric ependymoma patients who received proton therapy to determine if areas of normal tissue damage indicated by post-treatment image changes were associated with increased biological dose effectiveness. Material and Methods Fourteen of 34 children showed T2-FLAIR hyperintensity on post-treatment magnetic resonance (MR) images. We delineated regions of treatment-related change and calculated dose and linear energy transfer (LET) distributions with Monte Carlo. Voxel-level image change data were fit to a generalized linear model incorporating dose and LET. Cross-validation was used to determine model parameters and for receiver operating characteristic curve analysis. Tolerance dose (TD50; dose at which 50% of patients would experience toxicity) was interpolated from the model. Results Image changes showed dependence on increasing LET and dose. TD50 decreased with increasing LET, indicating an increase in biological dose effectiveness. The cross-validated area under the curve for the model was 0.91 (95% confidence interval 0.88–0.94). Conclusions Our correlation of changes on MR images after proton therapy with increased LET constitutes the first clinical evidence of variable proton biological effectiveness.

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“…As particles of a given energy of therapeutic interest traverse a medium, they lose energy continuously. The rate of energy loss per unit distance, i.e., the linear energy transfer (LET, defined mathematically as dE/dx ), increases first slowly and linearly and then very sharply near the end of the particle range (Figure 1 [1]). Increasing LET also leads to increasing ionization density along the particle track, which, in turn, leads to increasing amount and complexity of biological damage.…”

Section: Introductionmentioning

confidence: 99%

Radiobiological issues in proton therapy

et al. 2017

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Background The relative biological effectiveness (RBE) for particle therapy is a complex function of particle type, radiation dose, linear energy transfer (LET), cell type, endpoint, etc. In the clinical practice of proton therapy, the RBE is assumed to have a fixed value of 1.1. This assumption, along with the effects of physical uncertainties, may mean that the biologically effective dose distributions received by the patient may be significantly different from what is seen on treatment plans. This may contribute to unforeseen toxicities and/or failure to control the disease. Variability of Proton RBE It has been shown experimentally that proton RBE varies significantly along the beam path, especially near the end of the particle range. While there is now an increasing acceptance that proton RBE is variable, there is an ongoing debate about whether to change the current clinical practice. Clinical Evidence A rationale against the change is the uncertainty in the models of variable RBE. Secondly, so far there is no clear clinical evidence of the harm of assuming proton RBE to be 1.1. It is conceivable, however, that the evidence is masked partially by physical uncertainties. It is, therefore, plausible that reduction in uncertainties and their incorporation in the estimation of dose actually delivered may isolate and reveal the variability of RBE in clinical practice. Nevertheless, clinical evidence of RBE variability is slowly emerging as more patients are treated with protons and their response data are analyzed. Modelling and Incorporation of RBE in the Optimization of Proton Therapy The improvement in the knowledge of RBE could lead to better understanding of outcomes of proton therapy and in the improvement of models to predict RBE. Prospectively, the incorporation of such models in the optimization of intensity-modulated proton therapy could lead to improvements in the therapeutic ratio of proton therapy.

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Analysis of the track‐ and dose‐averaged LET and LET spectra in proton therapy using the geant4 Monte Carlo code

Cited by 111 publications

References 70 publications

Quality assurance in proton beam therapy using a plastic scintillator and a commercially available digital camera

Quality assurance in proton beam therapy using a plastic scintillator and a commercially available digital camera

Clinical evidence of variable proton biological effectiveness in pediatric patients treated for ependymoma

Radiobiological issues in proton therapy

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