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Development of a semi-analytical method for calculation of the radial dose profile for proton beams in the 0.5-1.0 MeV energy range
2004 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

There has been an increased interest in the application of protons for radiation therapy during the last decades. The main reason for this is the advantageous shape of the proton dose profile, which offers the possibility of improved treatment outcome. Proton beams and other light ions have because of this observed phenomenon a high efficiency to inflict lethal damage to tumor tissue while sparing normal tissue. Treatment with ions heavier than protons, have also been considered on the basis of radiological arguments. Recently scientists have discovered that not only high-energy electrons inflict severe damage to the DNA, but also low-energy electrons. Those electrons can be produced when protons with energy between 0.5-1 MeV interact with matter. High-accuracy calculations of dose distributions inside tumors and the surrounding tissue are essential for assessing the effectiveness of a given treatment in terms of probability of tumor control and of radiation-induced complications. The use of Monte Carlo methods to simulate radiation transport has become the most accurate means of predicting absorbed dose distributions and other quantities like numbers of track ends, track lengths and angular distributions. Today, there no accurate Monte-Carlo codes for proton transport, not even for low-energy electron transport. Much work is devoted to develop a Monte Carlo code for this purpose. However, for most practical cases in treatment planning, an advantageous solution has been found by combining the intrinsic accuracy of Monte Carlo methods with the swiftness of analytical techniques. In this work, a simple semi-analytical method is developed for fast dose distribution calculations for protons with energy range 0.5-1 MeV. The major part of the energy loss when protons traverse tissue, ends up in the ionizations of the target atoms. The double differential cross sections for this secondary electron production is calculated with Continuous distorted waves-eikonal initial state (CDW-EIS). Assume no energy attenuation of the point mono-directional mono-energetic proton beam in the interval of calculation and treat every interaction point along the beam axis as a virtual electron point source. The dose distribution from those electron sources calculates with the pencil beam concept and simulations of the central depth dose, needed for this, are made with the Monte Carlo code PENELOPE. Comparing the result with the widely accepted 1/r2 law and other calculations, both analytical and Monte Carlo simulations, gives good accordance with both the 1/r2 law and all the theories at intermediate radius. Underestimation at small radius compared to the other results is clearly seen. When the radius increases towards the ejected electron range maximum, the present result agrees better with a 1/r3 curve, same behavior as most of the other theories shows.

Place, publisher, year, edition, pages
Keyword [en]
Technology, Medical radiation physics, Protons, Dose distributions, cross, sections, CDW-EIS, PENELOPE, Monte Carlo
Keyword [sv]
URN: urn:nbn:se:ltu:diva-50449ISRN: LTU-EX--04/275--SELocal ID: 7b66000f-522d-4008-97e7-8262cb8682eeOAI: diva2:1023808
Subject / course
Student thesis, at least 30 credits
Educational program
Engineering Physics, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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