Attix free-air chamber correction factors computed using EGSnrc

IF 3.2 2区医学 Q1 RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING Medical physics Pub Date : 2025-01-25 DOI:10.1002/mp.17629

John T. Stasko, Wesley S. Culberson

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Abstract

Background

A cylindrical free-air chamber, the Attix FAC, is used for absolute air-kerma measurements of low-energy photon beams at the University of Wisconsin Medical Radiation Research Center. Correction factors for air-kerma measurements of specific beams were determined in the 1990s. In order to measure air-kerma rates of beams in development, new correction factors must be computed.

Purpose

We aimed to compute monoenergetic correction factors for air-kerma measurements with the Attix FAC that could be used to determine corrections for arbitrary polyenergetic beams.

Methods

A model of the Attix FAC was created in the Monte Carlo code, EGSnrc. The EGSnrc user codes, egs_fac, and egs_chamber, were utilized to calculate aperture transmission, scatter, collecting rod electron loss, and wall electron loss correction factors for incident monoenergetic photon beams with energies between 5 and 50 keV. Beam-specific correction factors were then derived from the monoenergetic correction factors and compared with the currently accepted values.

Results

Correction factors were computed in 0.5 keV intervals. The newly calculated beam-specific correction factors and the old conventional values agreed within 0.1% for all beams investigated.

Conclusions

The process for determining monoenergetic correction factors for air-kerma measurements with a free-air chamber is detailed in this work. Beam-specific correction factors can then be calculated if photon spectra are known. This process can be carried out for any free-air chamber, given specific materials and dimensions for modeling.

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使用EGSnrc计算Attix自由空气室校正因子。

背景：在威斯康星大学医学辐射研究中心，一个圆柱形自由空气室，Attix FAC，被用于低能光子光束的绝对空气-kerma测量。在20世纪90年代确定了特定光束的空气-kerma测量的修正系数。为了测量光束在发展过程中的空气速率，必须计算新的修正系数。目的：我们旨在用Attix FAC计算空气温度测量的单能校正因子，该因子可用于确定任意多能光束的校正。方法：在Monte Carlo代码EGSnrc中建立Attix FAC模型。利用EGSnrc用户代码egs_fac和egs_chamber计算了入射能量在5 ~ 50 keV之间的单能光子光束的孔径透射、散射、收集棒电子损失和壁电子损失修正因子。然后从单能校正因子推导出光束特定校正因子，并与目前接受的值进行比较。结果：以0.5 keV为间隔计算校正因子。新计算的光束特定校正因子和旧的常规值在所有研究光束的0.1%以内一致。结论：本文详细介绍了用自由空气室测定空气-kerma的单能校正因子的过程。如果光子光谱已知，则可以计算出光束特定的校正因子。这个过程可以进行任何自由空气室，给定特定的材料和尺寸的建模。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Medical physics 医学-核医学

CiteScore

6.80

自引率

15.80%

发文量

660

审稿时长

1.7 months

期刊介绍： Medical Physics publishes original, high impact physics, imaging science, and engineering research that advances patient diagnosis and therapy through contributions in 1) Basic science developments with high potential for clinical translation 2) Clinical applications of cutting edge engineering and physics innovations 3) Broadly applicable and innovative clinical physics developments Medical Physics is a journal of global scope and reach. By publishing in Medical Physics your research will reach an international, multidisciplinary audience including practicing medical physicists as well as physics- and engineering based translational scientists. We work closely with authors of promising articles to improve their quality.