利用百分比深度剂量重建法估算光子束能量谱的横向变化。

IF 1.7 Q3 RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING
Puspen Chakraborty, Hidetoshi Saitoh, Yuta Miyake, Tenyoh Suzuki, Weishan Chang
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引用次数: 0

摘要

在摩纳哥治疗计划系统(TPS)的光子塌缩锥卷积(pCCC)算法中,中心轴能谱被假定为在整个照射区域内恒定不变。为了考虑横向变化,在计算单位质量释放的总能量时,会对衰减系数应用离轴软化因子。我们通过对摩纳哥计算得出的深度剂量百分比(PDDs)和离轴比(OARs)进行比较研究,并在不同离轴角度和深度对 6 MV 光子束进行测量,从而对该方法进行评估。结果发现两者之间存在显著差异,相对差异超过 ± 1%。因此,这种方法可能无法准确表示能谱的横向变化。我们建议直接实施中心轴和离轴的能量谱,以提高大场剂量计算的准确性。为此,我们沿离轴角度从单能量深度剂量(MDDs)重建 PDDs,从而估算出作为径向距离函数的能谱。这种方法可以在不显著增加光束建模时间的情况下快速得出能量谱。MDD 是通过蒙特卡罗模拟(DOSRZnrc)计算得出的。使用广义还原梯度法将重建的 PDD 与测量的 PDD 之间的差异最小化,以优化能谱。沿着 0°、1.15°、2.29°、3.43°、4.57°、5.71°、6.84°、7.97°、9.09°、10.2° 的离轴角重建的 PDD 与测量值非常吻合(相对差异在 ± 0.5% 以内)。总之,我们提出的方法可以准确估计横向能谱变化,从而提高 pCCC 算法的剂量计算精度。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Estimation of the lateral variation of photon beam energy spectra using the percentage depth dose reconstruction method.

In photon-collapsed cone convolution (pCCC) algorithm of the Monaco treatment planning system (TPS), the central-axis energy spectrum is assumed constant throughout the entire irradiation area. To consider lateral variations, an off-axis softening factor is applied to attenuation coefficients during the total energy released per unit mass calculation. We evaluated this method through comparison studies of percentage depth doses (PDDs) and off-axis ratios (OARs) calculated by Monaco and measured for a 6 MV photon beam at various off-axis angles and depths. Significant differences were observed, with relative differences exceeding ± 1%. Therefore, this method may not accurately represent lateral variations of energy spectra. We propose directly implementing energy spectra on both central-axis and off-axis to improve dose calculation accuracy for large field. To this end, we introduce reconstruction of PDDs from monoenergetic depth doses (MDDs) along off-axis angles, thereby estimating energy spectra as functions of radial distance. This method derives energy spectra quickly without significantly increasing the beam modeling time. MDDs were computed through Monte Carlo simulations (DOSRZnrc). The variances between reconstructed and measured PDDs were minimized using the generalized-reduced-gradient method to optimize energy spectra. Reconstructed PDDs along off-axis angles of 0°, 1.15°, 2.29°, 3.43°, 4.57°, 5.71°, 6.84°, 7.97°, 9.09°, 10.2° to estimate energy spectra at radial distances of 0-18 cm in 2 cm increments and OARs calculated using estimated energy spectra at 5, 10, and 20 cm depths, well agreed with measurement (relative differences within ± 0.5%). In conclusion, our proposed method accurately estimates lateral energy spectrum variation, thereby improving dose calculation accuracy of pCCC algorithm.

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来源期刊
Radiological Physics and Technology
Radiological Physics and Technology RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING-
CiteScore
3.00
自引率
12.50%
发文量
40
期刊介绍: The purpose of the journal Radiological Physics and Technology is to provide a forum for sharing new knowledge related to research and development in radiological science and technology, including medical physics and radiological technology in diagnostic radiology, nuclear medicine, and radiation therapy among many other radiological disciplines, as well as to contribute to progress and improvement in medical practice and patient health care.
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