de Campos Tarcisio Passos Ribeiro, Nogueira Luciana Batista, Trindade Bruno, Cuperschmid Ethel Mizrahy
NRI - Nucleo de Radiações Ionizantes, Professor do Departamento de Engenharia Nuclear da Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.
Departamento de Anatomia e Imagem, Faculdade de Medicina, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.
Rep Pract Oncol Radiother. 2016 May-Jun;21(3):240-9. doi: 10.1016/j.rpor.2015.11.007. Epub 2016 Jan 4.
To provide a comparative dosimetric analysis of permanent implants of Ho(166)-seeds and temporary HDR Ir(192)-brachytherapy through computational simulation.
Brachytherapy with Ir(192)-HDR or LDR based on temporary wires or permanent radioactive seed implants can be used as dose reinforcement for breast radiation therapy. Permanent breast implants have not been a practical clinical routine; although, I(125) and Pd(103)-seeds have already been reported. Biodegradable Ho(166)-ceramic-seeds have been addressed recently.
Simulations of implants of nine Ho(166)-seeds and equivalent with HDR Ir(192)-brachytherapy were elaborated in MCNP5, shaped in a computational multivoxel simulator which reproduced a female thorax phantom. Spatial dose rate distributions and dose-volume histograms were generated. Protocol's analysis involving exposure time, seed's activities and dose were performed.
Permanent Ho(166)-seed implants presented a maximum dose rate per unit of contained activity (MDR) of 1.1601 μGy h(-1) Bq(-1); and, a normalized MDR in standard points (8 mm, equidistant to 03-seeds - SP1, 10 mm - SP2) of 1.0% (SP1) and 0.5% (SP2), respectively. Ir(192)-brachytherapy presented MDR of 4.3945 × 10(-3) μGy h(-1) Bq(-1); and, 30% (SP1), and 20% (SP2). Therefore, seed's implant activities of 333 MBq (Ho(166)) and 259 GBq (Ir(192)) produced prescribed doses of 58 Gy (SP1; 5d) and 56 Gy (SP1, 5 fractions, 6 min), respectively.
Breast Ho(166)-implants of 37-111 MBq are attractive due to the high dose rate near 6-10 mm from seeds, equivalent to Ir(192)-brachytherapy of 259 GBq (3 fractions, 6 min) providing similar dose in standard points at a week; however, with spatial dose distribution better confined. The seed positioning can be adjusted for controlling the breast tumor, in stages I and II, in flat and deep tumors, without any breast volumetric limitation.
通过计算模拟对钬（Ho）-166 种子永久性植入和高剂量率铱（Ir）-192 近距离治疗进行剂量学比较分析。
基于临时导线或永久性放射性种子植入的铱（Ir）-192 高剂量率或低剂量率近距离治疗可作为乳腺放射治疗的剂量增强手段。永久性乳腺植入尚未成为实际临床常规操作；尽管已有关于碘（I）-125 和钯（Pd）-103 种子的报道。可生物降解的钬（Ho）-166 陶瓷种子最近也已被提及。
在 MCNP5 中对九个钬（Ho）-166 种子植入及等效的铱（Ir）-192 高剂量率近距离治疗进行模拟，在一个计算多体素模拟器中构建模型，该模拟器再现了女性胸部体模。生成空间剂量率分布和剂量体积直方图。进行了涉及照射时间、种子活度和剂量的方案分析。
永久性钬（Ho）-166 种子植入每单位所含活度的最大剂量率（MDR）为 1.1601 μGy h⁻¹ Bq⁻¹；在标准点（距 03 颗种子等距 8 mm - SP1、10 mm - SP2）的归一化 MDR 分别为 1.0%（SP1）和 0.5%（SP2）。铱（Ir）-192 近距离治疗的 MDR 为 4.3945×10⁻³ μGy h⁻¹ Bq⁻¹；在 SP1 为 30%，在 SP2 为 20%。因此，333 MBq（钬（Ho）-166）和 259 GBq（铱（Ir）-192）的种子植入活度分别产生规定剂量的 58 Gy（SP1；5 天）和 56 Gy（SP1，5 次分割，每次 6 分钟）。
37 - 111 MBq 的乳腺钬（Ho）-166 植入具有吸引力，因为在距种子 6 - 10 mm 处剂量率高，相当于 259 GBq（3 次分割，每次 6 分钟）的铱（Ir）-192 近距离治疗，在一周内标准点提供相似剂量；然而，空间剂量分布限制更好。对于 I 期和 II 期的扁平及深部乳腺肿瘤，可调整种子位置以控制肿瘤，且不受任何乳腺体积限制。
