Monaco治疗计划系统中量化并构建电离室有效点计算模型

doi:10.3760/cma.j.issn.1004-4221.2018.10.009

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Abstract

Objective Because of statistical noise in Monte Carlo dose calculations,the effective point doses may not be accurately calculated. A user-defined sphere volume was adopted to substitute the effective point to take sphere sampling around the effective point,which minimize the random errors and improve the accuracy of statistical dose. Methods Direct dose measurements were performed at 0°and 90°using a 0.125 cm³ Semiflex ionization chamber (IC) 31010 isocentrically placed in the center of a homogeneous Cylindric sliced RW3 phantom (PTW,Germany).In the scanned CT phantom series,the sensitive volume length of the IC (6.5 mm) was delineated and the isocenter was defined as the simulated effective point. All beams were simulated in the treatment planning system (TPS) in accordance to the measured model. The grid spacing was calculated by 2 mm voxels and the relative standard deviation should be ≤0.5%.The statistical and measured doses were statistically compared among three IC models with different electron densities (ED;esophageal lumen ED=0.210 g/cm³ for model A,air ED=0.001 g/cm³ for model B and the default CT scanned ED for model C) at different sampling sphere radius (2.5,2.0,1.5 and 1.0 mm) to evaluate the effect of Monte Carlo.calculation uncertainty upon the dose accuracy. Results In the Monaco TPS,the statistical value was in the highest accordance with the measured value with an absolute average deviation of 0.49% when the IC was set as esophageal lumen ED=0.210 g/cm³ and the sampling sphere radius was 1.5 mm. When the IC was set as air ED=0.001 g/cm³ and default CT scanned ED,and,the recommended statistical sampling sphere radius was 2.5 mm,the absolute average deviations were 0.61% and 0.70%. Conclusion In the Monaco TPS,the calculation model with an ED of 0.210 g/cm³ and a sampling radius of 1.5 mm is recommended for the ionization chamber 31010 to substitute the effective point dose measurement to decrease the random stochastic errors of Monte Carlo.

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	Articles by authors
	Zhang Ruohui
	Bai Wenwen
	Gao Yulan
	Miao Mingchang
	Wang Shiguang
	Feng Yuanming
	Chi Zifeng

Key words： Monte Carlo Ionization chamber model Treatment planning system Sphere sampling

Received: 22 May 2017

Fund:

Hebei Provincial Natural Science Foundation of China (H2018206135)

Corresponding Authors: Feng Yuanming;Email: ymfeng@tju.edu.cn;Chi Zifeng,Email: chizf216@126.com

Cite this article:

Zhang Ruohui,Bai Wenwen,Gao Yulan et al. Quantification and construction of the effective point calculation model of ionization chamber in Monacao treatment planning system[J]. Chinese Journal of Radiation Oncology, 2018, 27(10): 916-919.

URL:

http://journal12.magtechjournal.com/Jweb_fszlx/EN/10.3760/cma.j.issn.1004-4221.2018.10.009 OR http://journal12.magtechjournal.com/Jweb_fszlx/EN/Y2018/V27/I10/916

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