Semnan University of Medical Sciences

Research and Technology Vice Chancellor

Shafiei, SeyedAli and Hasanzadeh, Hadi and Shafiei, SeyedAhmad (2012) A simple calculation method for determination of equivalent square field. Journal of Medical Physics, 37 (2). pp. 107-111. ISSN 0971-6203

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    Determination of the equivalent square fields for rectangular and shielded fields is of great importance in radiotherapy centers and treatment planning software. This is accomplished using standard tables and empirical formulas. The goal of this paper is to present a formula based on analysis of scatter reduction due to inverse square law to obtain equivalent field. Tables are published by different agencies such as ICRU (International Commission on Radiation Units and measurements), which are based on experimental data; but there exist mathematical formulas that yield the equivalent square field of an irregular rectangular field which are used extensively in computation techniques for dose determination. These processes lead to some complicated and time-consuming formulas for which the current study was designed. In this work, considering the portion of scattered radiation in absorbed dose at a point of measurement, a numerical formula was obtained based on which a simple formula was developed to calculate equivalent square field. Using polar coordinate and inverse square law will lead to a simple formula for calculation of equivalent field. The presented method is an analytical approach based on which one can estimate the equivalent square field of a rectangular field and may be used for a shielded field or an off-axis point. Besides, one can calculate equivalent field of rectangular field with the concept of decreased scatter radiation with inverse square law with a good approximation. This method may be useful in computing Percentage Depth Dose and Tissue-Phantom Ratio which are extensively used in treatment planning. Keywords: Equivalent square field, irregular field, Percentage Depth Dose, scattered beam, Tissue-Phantom Ratio

    Item Type: Article
    Subjects: R Medicine > R Medicine (General)
    Divisions: Faculty of Medical Sciences > School of Medicine
    Depositing User: Mr Vahab Moshtaghi
    Date Deposited: 26 Nov 2016 07:37
    Last Modified: 26 Nov 2016 07:37

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