Purpose The aim of this work is to develop a sensitometry model of EBT2 and EBT3 radiochromic films based on the observation that radiation induces growth of two polymer color phases. Methods Previously published data of the active layer absorption spectrum have been used to characterize the contribution to the total absorbance of each polymer color phase. Through a prior proposed external beam therapy absorption spectrum model the total absorbance has been deconvolved into two polymer phase contributions. The integral absorbance in the visible spectrum of each color phase has been calculated and parametrized as an absorbed dose function. A sensitometry model employing linear relationships with the color phase integral absorbances has been investigated. The phase linear coefficient ratio for each color channel is proposed to be a constant. Films belonging to six different production batches, three EBT2 and three EBT3, have been used to verify this model. Results Each polymer color phase integral absorbance in the visible spectrum has been expressed as a simple saturation function of the absorbed dose to the film. The data coming from the six production batches have been fitted to the proposed sensitometry model. This model predicts the measured dose variation in the active layer light attenuation up to fluctuations attributable to uncertainties. Conclusions The calibration curve can be written as a linear combination of simple functions describing the dose dependence of the integral absorbance of each polymer color phase. These functions are characteristics of the active layer material, and not dependent on the model and production batch. According to the proposed model, to calibrate a batch in terms of the active layer light attenuation consists of determining just one linear coefficient.
The aim of this work is to study a new analytical model which describes the dose-response curve in megavoltage photon beams of the radiochromic EBT3 film measured with two commercially available flatbed scanners. This model takes into account the different increase of the number of two types of absorbents in the film with absorbed dose and it allows to identify parameters that depend on the flatbed scanner and the film model, and parameters that exclusively depend on the production lot. In addition, the new model is also compared with other models commonly used in the literature in terms of its performance in reducing systematic calibration uncertainties. Methods and materials:The new analytical model consists on a linear combination of two saturating exponential functions for every color channel. The exponents modeling the growing of each kind of absorbent are film model and scanner model-dependent, but they do not depend on the manufacturing lot. The proposed model considers the different dose kinetics of each absorbent and the apparent effective behavior of one of the absorbents in the red color channel of the scanner. The dose-response curve has been measured using EBT3 films, a percentage depth dose (PDD) calibration method in a dose range between 0.5 and 25 Gy, and two flatbed scanners: a Microtek 1000 XL and an EPSON 11000 XL. The PDD calibration method allows to obtain a dense collection of calibration points which have been fitted to the proposed response curve model and to other published models. The fit residuals were used to evaluate the performance of each model compared with the new analytical model. Results:The model presented here does not introduce any systematic deviations up to the degree of accuracy reached in this work. The residual distribution is normally shaped and with lower variance than the distributions of the other published models. The model separates the parameters reflecting specific characteristics of the dosimetry system from the linear parameters which depend only on the production lot and are related to the relative abundance of each type of absorbent. The calibration uncertainty is reduced by a mean factor of two by using this model compared with the other studied models.
Los seres humanos se intercambian libremente productos y servi-cios en el mercado. El uso del dinero sustituyendo al trueque faci-litó la multiplicación de los intercambios. Los productos que flu-yen al mercado son libremente escogidos por los individuos, pero no ocurre lo mismo con la moneda utilizada que viene in-dicada por los gobiernos. Resulta contradictorio que el instru-mento más eficaz para el intercambio voluntario sea impuesto por los gobiernos y no sea resultado del acuerdo voluntario de los individuos, lo que impide que los ciudadanos puedan elegir la moneda más eficaz. El dinero surgió de forma espontáneo pero no casual. En dife-rentes puntos del planeta y en diversos períodos de tiempo surgie-ron monedas que facilitaban un intercambio de productos y servi-cios mucho más eficaz que con el trueque. Como toda innovación humana fue mejorando a lo largo del tiempo y diferentes bienes desempeñaron la función monetaria. Al final fueron los metales preciosos, especialmente el oro, los que se alzaron como los prefe-ridos para ser utilizados como dinero. Después surgieron otros bienes que sin apenas valor pasaron a ser utilizados como moneda como el caso del papel o las anota-ciones de cuenta. La existencia de un dinero sin respaldo en bien tangible alguno ha levantado numerosas suspicacias. Se le acha-ca que su aceptación entre los agentes acostumbrados a operar con monedas con respaldo se debió principalmente a la coacción estatal. No entienden otra forma de aceptar bienes sin apenas valor. ¿No podría ser que el dinero fiduciario fuera más eficiente? Cuando el oro actuaba como dinero su valor estaba compuesto por sus dos usos: el intrínseco del metal y el monetario. Éste úl-timo era fiduciario, es decir, se basaba en la fe de que el oro iba a ser aceptado para el intercambio comercial. Lo que ocurre con el actual dinero fiduciario es que el valor del material es ínfimo y la mayor parte de su valor total descansa en la utilidad que proporcione para facilitar las transacciones entre agentes. El dinero mercancía fue fructífero hasta que pasó a ser proporcio-nado por los gobiernos. No podemos juzgar al dinero sin respaldo material sólo por los ejemplos gestionados por el estado, igual que tampoco lo haríamos con el dinero mercancía. El dinero fi-duciario puede existir sin ningún tipo de respaldo estatal y ser el mejor dinero posible.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.