A phantom for 2D dose measurements in the vicinity of metal implants for photon and proton beams

IF 1.9 3区物理与天体物理 Q2 PHYSICS, MULTIDISCIPLINARY

Frontiers in Physics Pub Date : 2024-08-02 DOI:10.3389/fphy.2024.1433208

Wolfgang Lechner, Barbara Knäusl, Jacob Brunner, Dietmar Georg, Peter Kuess

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引用次数: 0

Abstract

This work aimed to characterize a dedicated phantom for assessing the dose near metal implants for radiotherapy with photons and protons. A dosimetry audit phantom was redesigned to position a Gafchromic EBT-3 film within a bisected titanium pedicle screw (6.5 mm diameter). The mass density and the water equivalent thickness (WET) of the phantom material were determined. The phantom was irradiated using a photon arc and a horizontal proton beam in combination with a couch rotation of 20°, with three repeated measurements each. Treatment plans utilizing a single field covering the screw and the EBT-3 film were optimized to deliver a physical dose of 2 Gy using a collapsed cone and Monte Carlo dose engine for photons and protons, respectively. The mass density and the WET of the phantom were determined as (1.033 ± 0.010) gcm−3 and (1.022 ± 0.013), respectively. Ionisation chamber measurements agreed within 1% (photons) and 0.5% (protons) with the calculated dose values. Relative photon dosimetry measurements using EBT-3 films revealed an agreement between measured and calculated horizontal profiles within the confidence interval for areas beyond 5 mm from the center. For photon plans, significant deviations of more than 10% were found at the interfaces between phantom material and screw. The proton measurements showed a gradual decrease of 3% across both profiles. In contrast to photon plans, no dose increase was measured within the screw, but significant dose fluctuations (>5%) in the beam’s exit region. This study showed that the behavior of dose engine is affected by metal implants and thus dosimetric measurements are highly recommended. The presented phantom can serve as foundation for dedicated end-2-end phantoms.

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用于光子和质子束金属植入物附近二维剂量测量的模型

这项研究旨在确定一个专用模型的特性，以评估使用光子和质子进行放射治疗时金属植入物附近的剂量。我们重新设计了一个剂量测定审核模型，将 Gafchromic EBT-3 薄膜放置在直径为 6.5 毫米的钛椎弓根螺钉内。测定了模型材料的质量密度和水等效厚度（WET）。使用光子弧和水平质子束结合旋转 20° 的沙发对模型进行照射，每次重复测量三次。利用覆盖螺钉和 EBT-3 薄膜的单场对治疗方案进行了优化，分别使用光子和质子的塌缩锥和蒙特卡洛剂量引擎，使物理剂量达到 2 Gy。模型的质量密度和 WET 分别确定为 (1.033 ± 0.010) gcm-3 和 (1.022 ± 0.013)。电离室测量结果与计算剂量值的吻合度分别为 1%（光子）和 0.5%（质子）。使用 EBT-3 胶片进行的相对光子剂量测定显示，在距离中心 5 毫米以外的区域，测量值和计算值的水平剖面一致性在置信区间内。对于光子计划，在模型材料和螺钉之间的界面上发现了超过 10% 的明显偏差。质子测量结果显示，两个剖面上的偏差逐渐减小了 3%。与光子计划不同的是，在螺钉内测得的剂量没有增加，但在射束出口区域测得的剂量波动很大（5%）。这项研究表明，剂量引擎的行为会受到金属植入物的影响，因此强烈建议进行剂量测定。该模型可作为专用端-2-端模型的基础。

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

Frontiers in Physics Mathematics-Mathematical Physics

CiteScore

4.50

自引率

6.50%

发文量

1215

审稿时长

12 weeks

期刊介绍： Frontiers in Physics publishes rigorously peer-reviewed research across the entire field, from experimental, to computational and theoretical physics. This multidisciplinary open-access journal is at the forefront of disseminating and communicating scientific knowledge and impactful discoveries to researchers, academics, engineers and the public worldwide.