Long-term stability of a PTW 34070 large-area parallel ionization chamber in clinical proton scanning beams

IF 2 4区医学 Q3 RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING

Journal of Applied Clinical Medical Physics Pub Date : 2024-09-16 DOI:10.1002/acm2.14525

Masashi Yamanaka, Yutaro Mori, Kazuki Matsumoto, Shunsuke Moriya, Akihiro Yamano, Takahiro Shimo, Ryosuke Shirata, Kazunori Nitta, Hironori Nagata, Koichi Tokuuye

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Abstract

Purpose

In the modeling of beam data for proton therapy planning systems, absolute dose measurements are performed utilizing a Bragg peak chamber (BPC), which is a parallel-plate ionization chamber. The long-term stability of the BPC is crucial for ensuring accurate absolute dose measurement. The study aims to assess the long-term stability of the BPC in clinical proton pencil beam scanning delivery.

Methods

The long-term stability evaluation focused on the BPC-Type 34070 (PTW Freiburg, Germany), utilizing clinical proton scanning beams from December 2022 to November 2023. Monthly investigations were conducted to evaluate the response and cross-calibration factor of the BPC and a reference chamber, employing the spread-out Bragg peak (SOBP) field. Additionally, assessments were made regarding the BPC's response to monoenergetic beams, along with an examination of the impact of polarity and ion recombination on the BPC.

Results

The response and cross-calibration factor of the BPC varied up to 1.9% and 1.8%, respectively, while the response of the reference chamber remained within a 0.5% range. The BPC's response to the mono-energetic beams varied up to 2.0% across all energies, demonstrating similar variation trends in both the SOBP field and mono-energetic beams. Furthermore, the variations in polarity and ion recombination effect remained stable within a 0.4% range throughout the year. Notably, the reproducibility of the BPC remained high for each measurement conducted, whether for the SOBP field or mono-energetic beams, with a maximum deviation observed at 0.1%.

Conclusions

The response and cross-calibration factor of the BPC demonstrated significant variations, with maximum changes of 1.9% and 1.8%, respectively. However, the reproducibility of the BPC remained consistently high for each measurement. It is recommended that when conducting absolute dose measurements using a BPC, its response should be compared and corrected against the reference chamber for each measurement.

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PTW 34070 大面积平行电离室在临床质子扫描束中的长期稳定性

目的在质子治疗计划系统的射束数据建模中，绝对剂量测量是利用平行板电离室布拉格峰室（BPC）进行的。BPC 的长期稳定性对于确保精确的绝对剂量测量至关重要。研究旨在评估 BPC 在临床质子铅笔束扫描传输中的长期稳定性。方法长期稳定性评估主要针对 34070 型 BPC（德国弗莱堡 PTW 公司），在 2022 年 12 月至 2023 年 11 月期间使用临床质子扫描束。每月进行一次调查，利用扩散布拉格峰（SOBP）场评估 BPC 和参考室的响应和交叉校准因子。此外，还对 BPC 对单能量光束的响应进行了评估，并检查了极性和离子重组对 BPC 的影响。在所有能量下，BPC 对单能量光束的响应变化高达 2.0%，显示出 SOBP 场和单能量光束的类似变化趋势。此外，极性和离子重组效应的变化全年稳定在 0.4% 的范围内。值得注意的是，无论是 SOBP 磁场还是单能量光束，BPC 在每次测量中的再现性都很高，观察到的最大偏差为 0.1%。不过，BPC 在每次测量中的再现性始终很高。建议在使用 BPC 进行绝对剂量测量时，每次测量都应将其响应与参比室进行比较和校正。

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

Journal of Applied Clinical Medical Physics 医学-核医学

CiteScore

3.60

自引率

19.00%

发文量

331

审稿时长

3 months

期刊介绍： Journal of Applied Clinical Medical Physics is an international Open Access publication dedicated to clinical medical physics. JACMP welcomes original contributions dealing with all aspects of medical physics from scientists working in the clinical medical physics around the world. JACMP accepts only online submission. JACMP will publish: -Original Contributions: Peer-reviewed, investigations that represent new and significant contributions to the field. Recommended word count: up to 7500. -Review Articles: Reviews of major areas or sub-areas in the field of clinical medical physics. These articles may be of any length and are peer reviewed. -Technical Notes: These should be no longer than 3000 words, including key references. -Letters to the Editor: Comments on papers published in JACMP or on any other matters of interest to clinical medical physics. These should not be more than 1250 (including the literature) and their publication is only based on the decision of the editor, who occasionally asks experts on the merit of the contents. -Book Reviews: The editorial office solicits Book Reviews. -Announcements of Forthcoming Meetings: The Editor may provide notice of forthcoming meetings, course offerings, and other events relevant to clinical medical physics. -Parallel Opposed Editorial: We welcome topics relevant to clinical practice and medical physics profession. The contents can be controversial debate or opposed aspects of an issue. One author argues for the position and the other against. Each side of the debate contains an opening statement up to 800 words, followed by a rebuttal up to 500 words. Readers interested in participating in this series should contact the moderator with a proposed title and a short description of the topic