Sensitivity of contributing factors to heterogeneity corrections in dosimetry of ocular brachytherapy using iodine-125 COMS plaques.

IF 1.1 4区 医学 Q4 ONCOLOGY
Journal of Contemporary Brachytherapy Pub Date : 2024-10-01 Epub Date: 2024-10-18 DOI:10.5114/jcb.2024.144232
Yongsook C Lee, Mehran Nik Akhtar, Yongbok Kim, Jae Won Jung
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引用次数: 0

Abstract

Purpose: To investigate sensitivity of contributing factors to heterogeneity corrections in ocular brachytherapy using iodine-125 (125I) Collaborative Ocular Melanoma Study (COMS) plaques.

Material and methods: Using egs_brachy, Monte Carlo (MC) simulations were performed for 125I COMS plaques (model: IsoAid IAI-125A). Homogeneous dose (DHOMO) was estimated under the American Association of Physicists in Medicine Task Group-43 assumptions, with 85 Gy prescribed to a 5 mm depth. Heterogeneous doses (DHETERO#1-#7) were determined with medium-heterogeneity for the following scenarios: #1. Modulay backing (M) alone, #2. Silastic insert (S) alone, #3. Interseed attenuation effects (I) alone, #4. M + S, #5. M + I, #6. S + I, and #7. M + S + I. For scenarios #1-#7, heterogeneity correction factors (HCFs) were derived from DHETERO#1-#7/DHOMO for central axis points up to 22 mm, and for off-axis points (i.e., optic disc, macula, and lens) as a function of distance from tumor to optic disc (DT) or macula (MT), and tumor dimensions in the direction of optic disc (BD) or macula (BM).

Results: For a 16-mm diameter COMS plaque, in central axis, the dominant factor to heterogeneity corrections (dose reduction by 9.5-13.8% with heterogeneity) was Silastic insert at a depth ≤ 5 mm, whereas both Modulay backing and Silastic insert were contributing (range, 12.2-19.0%) at deeper depths. For off-axis, Silastic insert was the major factor to heterogeneity corrections (≥ 11.8%) at DT (MT) ≤ 6.9 (7.6) mm for optic disc (macula) and (range, 8.9-10.0%) at MT > 18.5 mm for lens, but both Modulay backing and Silastic insert were contributing (range, 18.3-24.4%) at farther DT (MT) for optic disc (macula) and (range, 12.8-18.2%) at MT ≤ 18.5 mm for lens. Interseed effects were small (≤ 1.7% for central axis and ≤ 2.3% for off-axis). Data for the other six plaques (10-14 mm and 18-22 mm diameter) presented similar trends.

Conclusions: The use of universal HCF(s) for the two dominant factors determined in this study will facilitate heterogeneous dose estimates for each clinical scenario without an MC tool.

碘-125 COMS斑块眼近距离放射治疗剂量测定中影响异质性校正因素的敏感性
目的:探讨影响碘-125 (125I)协同眼黑色素瘤研究(COMS)斑块眼近距离放射治疗异质性校正因素的敏感性。材料和方法:使用egs_brachy,对125I COMS斑块(模型:IsoAid IAI-125A)进行蒙特卡罗(MC)模拟。均匀剂量(DHOMO)是根据美国医学物理学家协会第43任务组的假设估计的,规定5mm深度为85 Gy。在以下情况下,异质性剂量(DHETERO#1-#7)以中等异质性确定:模块支持(M)单独,#2。单独的硅橡胶插入(S), #3。种间衰减效应(I)单独,#4。M + s, #5。M + i, #6。S + I和#7。M + S + I.对于场景#1-#7,非均质性校正因子(hcf)由DHETERO#1-#7/DHOMO导出,用于中轴线点高达22 mm,对于离轴点(即视盘、黄斑和晶状体),作为肿瘤到视盘(DT)或黄斑(MT)的距离以及视盘(BD)或黄斑方向的肿瘤尺寸(BM)的函数。结果:对于直径为16mm的COMS斑块,在中心轴上,在深度≤5mm处,硅橡胶衬垫对非均匀性校正(剂量减少9.5-13.8%)起主导作用,而在更深的深度处,Modulay衬垫和硅橡胶衬垫都起作用(范围为12.2-19.0%)。在离轴情况下,硅橡胶垫片是影响视盘(黄斑)DT≤6.9 (7.6)mm和透镜在MT≤18.5 mm处(范围8.9-10.0%)非均质性校正的主要因素,但在更远的DT (MT)处(范围18.3-24.4%)视盘(黄斑)和透镜在MT≤18.5 mm处(范围12.8-18.2%),Modulay垫片和硅橡胶垫片都有贡献(范围18.3-24.4%)。种间效应较小(中轴≤1.7%,离轴≤2.3%)。其他6个斑块(直径10-14毫米和18-22毫米)的数据也呈现类似的趋势。结论:在本研究中确定的两个主要因素中使用通用HCF将有助于在没有MC工具的情况下对每种临床情况进行异质性剂量估计。
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 Contemporary Brachytherapy
Journal of Contemporary Brachytherapy ONCOLOGY-RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING
CiteScore
2.40
自引率
14.30%
发文量
54
审稿时长
16 weeks
期刊介绍: The “Journal of Contemporary Brachytherapy” is an international and multidisciplinary journal that will publish papers of original research as well as reviews of articles. Main subjects of the journal include: clinical brachytherapy, combined modality treatment, advances in radiobiology, hyperthermia and tumour biology, as well as physical aspects relevant to brachytherapy, particularly in the field of imaging, dosimetry and radiation therapy planning. Original contributions will include experimental studies of combined modality treatment, tumor sensitization and normal tissue protection, molecular radiation biology, and clinical investigations of cancer treatment in brachytherapy. Another field of interest will be the educational part of the journal.
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