Impact of extended source-to-surface distances and respiratory motion on the precision of electron beam therapy

IF 2.2 4区医学 Q3 RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING

Journal of Applied Clinical Medical Physics Pub Date : 2025-10-10 DOI:10.1002/acm2.70301

Takaaki Ito, Hiroyuki Kosaka, Yuya Yanagi, Yusuke Sakai, Hajime Monzen

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引用次数: 0

Abstract

Purpose

In electron beam therapy targeting superficial thoracic and abdominal lesions, the source-to-surface distance (SSD) varies due to patient respiration. This study aimed to investigate the percentage depth dose (PDD) and off-center ratio (OCR) of 6, 9, and 12 MeV electron beams at extended SSDs; and to assess the variations in dose caused by respiratory motion.

Methods

PDDs and OCRs for 6, 9, and 12 MeV electron beams were measured using a Blue Phantom 2 with 5 cm circular aperture and 10 × 10 cm² fields at SSDs ranging from 98 to 105 cm. The dose differences at the maximum depth (d_max) were calculated relative to an SSD of 100 cm. We simulated patient respiratory motion of 0–4 cm during irradiation with 5 cm circular aperture and 10 × 10 cm² fields by placing a water-equivalent phantom with a parallel-plate ionization chamber on a QUASAR Platform. The gantry angle was set to 270°, and the SSD was set to 100 cm. The dose differences at d_max were calculated relative to a motion amplitude of 0 cm.

Results

Extending the SSD by 3 cm reduced the dose by > 5% for all energies. For a 6 MeV electron beam with a 5 cm circular aperture, extending the SSD to 105 cm resulted in a dose reduction of 13.42% and expansions of the field size by 2.0 mm and the penumbra by 4.2 mm. A respiratory motion amplitude of 3 cm resulted in dose variations of > 3% for all energies and field sizes. The largest dose difference of 5.36% was observed for a 6 MeV electron beam with a 5 cm circular aperture.

Conclusions

The results demonstrate that extending the SSD by 3 cm reduced the dose by >5% for all energies, providing a useful quantitative benchmark for quality assurance in superficial electron therapy. Respiratory motion management may be warranted for electron beam therapy when respiratory-induced SSD variations exceed 3 cm.

Abstract Image

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源表面距离和呼吸运动对电子束治疗精度的影响

目的在电子束治疗胸部和腹部浅表病变时，由于患者呼吸的不同，电子束源到表面的距离也不同。本研究旨在探讨6、9、12 MeV电子束在扩展ssd上的百分比深度剂量（PDD）和离心比（OCR）；并评估由呼吸运动引起的剂量变化。方法采用5 cm圆孔径和10 × 10 cm2场的Blue Phantom 2，测量6、9和12 MeV电子束在固态硬盘范围为98 ~ 105 cm处的pdd和ocr。在最大深度（dmax）的剂量差计算相对于100厘米的SSD。我们在类星体平台上放置了一个具有平行板电离室的水等效模体，模拟了5 cm圆孔径和10 × 10 cm2场照射下患者0-4 cm的呼吸运动。龙门角度设置为270°，SSD设置为100 cm。相对于0 cm的运动幅度，计算了dmax处的剂量差。结果SSD延长3cm，各能量剂量均降低5%。对于直径为5cm、直径为6mev的电子束，将SSD延伸至105cm，可使辐照剂量降低13.42%，场尺寸扩大2.0 mm，半影面积扩大4.2 mm。呼吸运动幅度为3cm导致所有能量和场大小的剂量变化为3%。孔径为5 cm的6 MeV电子束的最大剂量差为5.36%。结论延长3 cm可使所有能量的剂量降低5%，为表浅电子治疗的质量保证提供了一个有用的定量基准。当呼吸诱导的SSD变化超过3cm时，电子束治疗可能需要呼吸运动管理。

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