A Verification of Electron Dose Calculation of a Treatment Planning System Using Monte Carlo Algorithm

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Thanyaporn Phochot Somvilai Chakrabandhu Somsak Wanwilairat

Abstract

A part of efficiency of treatment is strongly depending on accuracy of dose calculation, which should be
evaluated before implement in a clinical service. The object of this study was to verify the accuracy of
electron dose calculation for treatment planning system using Monte Carlo algorithm at depth Dmax, R90
and R50. The test cases following AAPM TG 53, including seven geometries, namely standard source to
surface distance (SSD), extended SSD, irregular field, irregular surface 30บ slopes, irregular surface 90 ํ
step, internal heterogeneity and adjacent beams were used to verify. This study compared in two types
of difference which using Van Dyk’s criteria of acceptability to evaluate for accuracy. The first was percentage
of dose difference that was compared between the result of calculation and measurement at central axis
in water with ionization. The second was comparison dose distribution by gamma passing rate using 2D
array detector in solid water phantom. The result of percentage of dose difference between calculation
and measurement for standard SSD and extended SSD were -1.5% to 0.5%. Irregular field was -0.1% to
2.8%. The gamma passing rate was 100% in all geometry with gamma index 4%/4 mm. The average relative
error of all these geometries was acceptable and the electron dose calculation of treatment planning system
had accuracy that was acceptable from Van Dyk’s criteria and could be used in the clinical service.

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Research Article