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SOBRE LA POSIBILIDAD DE USAR EL MÉTODO DE REGULARIZACIÓN DE TIKHONOV PARA RECONSTRUIR EL ESPECTRO DE ENERGÍA DE UN HAZ CLÍNICO DE ELECTRONES
ON THE POSSIBILITY OF USE THE TIKHONOV REGULARIZATION METHOD TO RECONSTRUCT THE ENERGY SPECTRUM OF A CLINICAL ELECTRON BEAM
Keywords:
Fotones Contaminantes, Fredholm, Índice Gamma, PENELOPE (es)Contamination Photons, Fredholm, Gamma Index, PENELOPE. (en)
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En radioterapia, el espectro de energía de electrones es la característica más importante para modelar la fuente de radiación cuando el propósito sea el cálculo exacto de la dosis. Usualmente, tres métodos son explorados la obtención del espectro: (i) simulación de la fuente vía Monte Carlo; (ii) medición directa vía un espectrómetro magnético y (iii) reconstrucción inversa. De entre ellos, reconstrucción inversa, a pesar de no ser el más exacto, es considerado el más apropiado por su simplicidad y rapidez. Reconstrucción inversa tiene por objeto extraer el espectro de energía a partir de la distribución de dosis en profundidad.
Ya que reconstrucción inversa es un problema mal definido, el método de regularización de Tikhonov es usado para superar la mala definición del problema y con ello obtener el espectro. La idoneidad de la reconstrucción es evaluada usando el índice gamma. Los resultados muestran que la regularización de Tikhonov es capaz de reconstruir el espectro de energía de un haz de electrones dentro del criterio clínico de aceptación del índice gamma > 95 % para 1 %/1 mm.
In radiotherapy, the electron energy spectrum is the most important characteristic for modelling the radiation source whose purpose is an accurate dose calculation.There are mainly three approaches to obtain the energy spectrum: (i) simulation of the source via Monte Carlo; (ii) direct measurement via a magnetic spectrometer and (iii) inverse reconstruction using an appropriate mathematical model. Among them, inverse reconstruction is considered the most appropriate for its simplicity and speed despite not being the most accurate. Since inverse reconstruction is an ill-posed problem the Tikhonov regularization is used to overcome this problem and thereby obtain the spectrum. The reconstruction success is evaluated using the gamma index. Results show Tikhonov regularization is able of reconstructing the energy spectrum of a clinical electron beam for the gamma index clinical acceptance of> 95 % within 1 %/1 mm.
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