Beam collimation and filtration optimization for a novel orthovoltage radiotherapy system

IF 3.2 2区医学 Q1 RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING

Medical physics Pub Date : 2025-02-06 DOI:10.1002/mp.17662

Nathan Clements, Olivia Masella, Deae-Eddine Krim, Lane Braun, Magdalena Bazalova-Carter

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引用次数: 0

Abstract

Background

The inaccessibility of clinical linear accelerators in low- and middle-income countries creates a need for low-cost alternatives. Kilovoltage (kV) x-ray tubes have shown promise as a source that could meet this need. However, performing radiotherapy with a kV x-ray tube has numerous difficulties, including high skin dose, rapid dose fall-off, and low dose rates. These limitations create a need for highly effective beam collimation and filtration.

Purpose

To improve the treatment potential of a novel kV x-ray system by optimizing an iris collimator and beam filtration using Bayesian techniques and Monte Carlo (MC) simulations.

Methods

The Kilovoltage Optimized AcceLerated Adaptive therapy system's current beam configuration consists of a 225 kVp x-ray tube, a 12-leaflet tungsten iris collimator, and a 0.1 mm copper filter. A Bayesian optimization was performed for the large and small focal spot sizes of the kV x-ray tube source at 220 kVp using TopasOpt, an open-source library for optimization in TOPAS. Collimator thickness, copper filter thickness, source-to-collimator distance (SCD), and source-to-surface distance (SSD) were the variables considered in the optimization. The objective function was designed to maximize the dose rate and the dose at a depth of 5 cm while minimizing the beam penumbra width and the out-of-field dose (OFD), all evaluated in a water phantom. Post-optimization, the optimal beam configuration was simulated and compared to the existing configuration.

Results

The optimal collimation setup consisted of 2.5 mm thick tungsten leaflets for the iris collimator and a 350 mm SSD for both focal spot sizes. The optimal copper filtration was 0.22 mm for the large focal spot and 0.15 mm for the small focal spot, with a SCD of 148.5 mm for the large focal spot and 125.8 mm for the small focal spot. For the large focal spot, the surface dose rate decreased by 9.4%, while the PDD at 5cm depth ( ${PDD}_{5 c m}$ ) increased by 7.7% compared to the existing iris collimator. Additionally, the surface beam penumbra width was reduced by 31.3%, and no significant changes in the OFD were observed. For the small focal spot, the surface dose rate for the new collimator increased by 3.7% and the ${PDD}_{5 c m}$ increased by 5.3%, with no statistically significant changes in the beam penumbra width or OFD.

Conclusion

The optimal beam collimation and filtration for both x-ray tube focal spot sizes of a kV radiotherapy system was determined using Bayesian optimization and MC simulations and resulted in improved dose distributions.

Abstract Image

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一种新型正电压放射治疗系统的光束准直和滤波优化。

背景：低收入和中等收入国家无法获得临床线性加速器，因此需要低成本替代品。千伏x射线管有望成为满足这一需求的光源。然而，使用千伏x射线管进行放射治疗有许多困难，包括皮肤剂量高、剂量下降快和剂量率低。这些限制产生了对高效光束准直和过滤的需求。目的：利用贝叶斯技术和蒙特卡罗（MC）模拟优化虹膜准直器和光束滤波，以提高新型千伏x射线系统的治疗潜力。方法：千伏优化加速适应治疗系统的当前光束配置由225 kVp x射线管、12片钨光圈准直器和0.1 mm铜滤光片组成。利用TopasOpt （TOPAS中用于优化的开源库）对220 kVp下kV x射线管源的大小焦斑进行了贝叶斯优化。准直器厚度、铜滤波器厚度、源到准直器距离（SCD）和源到表面距离（SSD）是优化中考虑的变量。目标函数设计为最大化剂量率和5cm深度处的剂量，同时最小化光束半影宽度和场外剂量（OFD），所有这些都在水影中进行评估。优化后，对优化后的梁结构进行了仿真，并与现有结构进行了比较。结果：最佳准直装置包括2.5 mm厚的钨片作为虹膜准直器，350 mm的固态硬盘用于两种焦斑尺寸。铜的最佳过滤效果为大焦斑0.22 mm，小焦斑0.15 mm，大焦斑SCD为148.5 mm，小焦斑SCD为125.8 mm。对于大焦斑，表面剂量率降低了9.4%，而5cm深度的PDD （PDD 5cm $\text{PDD}_{5\textnormal {cm}}$）比现有的虹膜准直器增加了7.7%。此外，表面光束半影宽度减少了31.3%，而OFD没有明显变化。对于小焦斑，新准直器的表面剂量率增加了3.7%,PDD 5 cm $\text{PDD}_{5\textnormal {cm}}$增加了5.3%，光束半影宽度和OFD没有统计学意义的变化。结论：通过贝叶斯优化和MC模拟，确定了kV放射治疗系统x射线管焦斑大小的最佳光束准直和滤波，改善了剂量分布。

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.