使用质量指数对诊断千伏 X 射线束的纳米点 OSLD 响应进行蒙特卡罗确定。

Monte Carlo determination of a nanoDot OSLD response using quality index for diagnostic kilovoltage X-ray beams.

机构信息

Department of Health Sciences, Faculty of Life Sciences, Kumamoto University, 4-24-1 Kuhonji, Chuo-ku, Kumamoto 862-0976, Japan.

出版信息

Phys Med. 2021 Apr;84:101-108. doi: 10.1016/j.ejmp.2021.03.031. Epub 2021 Apr 19.

DOI:10.1016/j.ejmp.2021.03.031

PMID:33887616

Abstract

PURPOSE

This study aims to investigate the energy response of an optically stimulated luminescent dosimeter known as nanoDot for diagnostic kilovoltage X-ray beams via Monte Carlo calculations.

METHODS

The nanoDot response is calculated as a function of X-ray beam quality in free air and on a water phantom surface using Monte Carlo simulations. The X-ray fluence spectra are classified using the quality index (QI), which is defined as the ratio of the effective energy to the maximum energy of the photons. The response is calculated for X-ray fluence spectra with QIs of 0.4, 0.5, and 0.6 with tube voltages of 50-137.6 kVp and monoenergetic photon beams. The surface dose estimated using the calculated response is verified by comparing it with that measured using an ionization chamber.

RESULTS

The nanoDot response in free air for monoenergetic photon beams (QI = 1.0) varies significantly at photon energies below 100 keV and reaches a factor of 3.6 at 25-30 keV. The response differs by up to approximately 6% between QIs of 0.4 and 0.6 for the same half-value layer (HVL). The response at the phantom surface decreases slightly owing to the backscatter effect, and it is almost independent of the field size. The agreement between the surface dose estimated using the nanoDot and that measured using the ionization chamber for assessing X-ray beam qualities is less than 2%.

CONCLUSIONS

The nanoDot response is indicated as a function of HVL for the specified QIs, and it enables the direct surface dose measurement.

摘要

目的

本研究旨在通过蒙特卡罗计算，研究一种名为 nanoDot 的光激励发光剂量计对诊断千伏 X 射线的能量响应。

方法

使用蒙特卡罗模拟，在自由空气中和水模表面上，将 nanoDot 响应计算为 X 射线束质的函数。使用质量指数 (QI) 对 X 射线注量谱进行分类，QI 定义为光子的有效能量与最大能量之比。对于 QI 为 0.4、0.5 和 0.6 的 X 射线注量谱，计算了管电压为 50-137.6 kVp 和单能光子束的响应。通过将计算得到的响应与使用电离室测量的表面剂量进行比较，验证了估算的表面剂量。

结果

在自由空气中，对于单能光子束（QI = 1.0），光子能量低于 100 keV 时，nanoDot 响应变化显著，在 25-30 keV 时达到 3.6 倍。对于相同的半价层 (HVL)，QI 为 0.4 和 0.6 之间的响应差异最大约为 6%。由于背散射效应，在水模表面的响应略有下降，并且几乎与射野大小无关。使用 nanoDot 估算的表面剂量与使用电离室评估 X 射线束质的测量值之间的一致性小于 2%。