Lee Yongsook C, Akhtar Mehran Nik, Kim Yongbok, Jung Jae Won
Department of Radiation Oncology, Miami Cancer Institute, Baptist Health South Florida, Miami, Florida, USA.
Department of Radiation Oncology, Herbert Wertheim College of Medicine, Florida International University, Miami, Florida, USA.
J Contemp Brachytherapy. 2024 Oct;16(5):371-382. doi: 10.5114/jcb.2024.144232. Epub 2024 Oct 18.
To investigate sensitivity of contributing factors to heterogeneity corrections in ocular brachytherapy using iodine-125 (I) Collaborative Ocular Melanoma Study (COMS) plaques.
Using egs_brachy, Monte Carlo (MC) simulations were performed for I COMS plaques (model: IsoAid IAI-125A). Homogeneous dose (D) 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 (D) 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 D/D 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).
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.
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.
研究使用碘 - 125（I）协作性眼黑色素瘤研究（COMS）敷贴器进行眼近距离治疗时，各影响因素对不均匀性校正的敏感性。
使用egs_brachy进行蒙特卡罗（MC）模拟，针对I型COMS敷贴器（型号：IsoAid IAI - 125A）。根据医学物理家协会任务组 - 43的假设估算均匀剂量（D），规定5 mm深度处的剂量为85 Gy。在以下情况下，以中等不均匀性确定不均匀剂量（D）：#1. 仅模块背衬（M），#2. 仅硅橡胶插入物（S），#3. 仅籽源间衰减效应（I），#4. M + S，#5. M + I，#6. S + I，以及#7. M + S + I。对于情况#1 - #7，不均匀性校正因子（HCF）由中心轴点至22 mm处的D/D得出，对于离轴点（即视盘、黄斑和晶状体），其作为从肿瘤到视盘（DT）或黄斑（MT）的距离以及肿瘤在视盘（BD）或黄斑（BM）方向尺寸的函数。
对于直径16 mm的COMS敷贴器，在中心轴上，不均匀性校正的主要因素（不均匀性导致剂量降低9.5 - 13.8%）在深度≤5 mm时为硅橡胶插入物，而在更深深度时，模块背衬和硅橡胶插入物均有影响（范围为12.2 - 19.0%）。对于离轴情况，在视盘（黄斑）的DT（MT）≤6.9（7.）mm时，硅橡胶插入物是不均匀性校正的主要因素（≥11.8%），对于晶状体，在MT > 18.5 mm时为（范围8.9 - 10.0%），但在视盘（黄斑）更远的DT（MT）时，模块背衬和硅橡胶插入物均有影响（范围18.3 - 24.4%），对于晶状体，在MT≤18.5 mm时为（范围12.8 - 18.2%）。籽源间效应较小（中心轴≤1.7%，离轴≤2.3%）。其他六个敷贴器（直径10 - 14 mm和18 - 22 mm）的数据呈现类似趋势。
使用本研究确定的两个主要因素的通用HCF，将有助于在无需MC工具的情况下，针对每种临床情况估算不均匀剂量。
