Ho Than Minh-Tri, Munro Iii John J, Medich David C
Worcester Polytechnic Institute.
J Appl Clin Med Phys. 2015 May 8;16(3):5270. doi: 10.1120/jacmp.v16i3.5270.
The Source Production & Equipment Co. (SPEC) model M-15 is a new Iridium-192 brachytherapy source model intended for use as a temporary high-dose-rate (HDR) brachytherapy source for the Nucletron microSelectron Classic afterloading system. The purpose of this study is to characterize this HDR source for clinical application by obtaining a complete set of Monte Carlo calculated dosimetric parameters for the M-15, as recommended by AAPM and ESTRO, for isotopes with average energies greater than 50 keV. This was accomplished by using the MCNP6 Monte Carlo code to simulate the resulting source dosimetry at various points within a pseudoinfinite water phantom. These dosimetric values next were converted into the AAPM and ESTRO dosimetry parameters and the respective statistical uncertainty in each parameter also calculated and presented. The M-15 source was modeled in an MCNP6 Monte Carlo environment using the physical source specifications provided by the manufacturer. Iridium-192 photons were uniformly generated inside the iridium core of the model M-15 with photon and secondary electron transport replicated using photoatomic cross-sectional tables supplied with MCNP6. Simulations were performed for both water and air/vacuum computer models with a total of 4 × 109 sources photon history for each simulation and the in-air photon spectrum filtered to remove low-energy photons belowδ = 10 keV. Dosimetric data, including D·(r,θ), gL(r), F(r,θ), φan(r), and φ-an, and their statistical uncertainty were calculated from the output of an MCNP model consisting of an M-15 source placed at the center of a spherical water phantom of 100 cm diameter. The air kerma strength in free space, SK, and dose rate constant, Λ, also was computed from a MCNP model with M-15 Iridium-192 source, was centered at the origin of an evacuated phantom in which a critical volume containing air at STP was added 100 cm from the source center. The reference dose rate, D·(r0,θ0) ≡ D· (1cm,π/2), is found to be 4.038 ± 0.064 cGy mCi-1 h-1. The air kerma strength, SK, is reported to be 3.632 ± 0.086 cGy cm2 mCi-1 g-1, and the dose rate constant, Λ, is calculated to be 1.112 ± 0.029 cGy h-1 U-1. The normalized dose rate, radial dose function, and anisotropy function with their uncertainties were computed and are represented in both tabular and graphical format in the report. A dosimetric study was performed of the new M-15 Iridium-192 HDR brachytherapy source using the MCNP6 radiation transport code. Dosimetric parameters, including the dose-rate constant, radial dose function, and anisotropy function, were calculated in accordance with the updated AAPM and ESTRO dosimetric parameters for brachytherapy sources of average energy greater than 50 keV. These data therefore may be applied toward the development of a treatment planning program and for clinical use of the source.
源生产与设备公司（SPEC）的M-15型是一种新型铱-192近距离放射治疗源型号，旨在用作Nucletron microSelectron Classic后装系统的临时高剂量率（HDR）近距离放射治疗源。本研究的目的是按照美国医学物理学家协会（AAPM）和欧洲放射肿瘤学会（ESTRO）针对平均能量大于50 keV的同位素所推荐的方法，通过获取M-15的一整套蒙特卡罗计算剂量学参数，来对这种HDR源进行临床应用特性描述。这是通过使用MCNP6蒙特卡罗代码来模拟在一个虚拟无限水模体中各个点处产生的源剂量学来实现的。接下来，将这些剂量学值转换为AAPM和ESTRO剂量学参数，并计算并给出每个参数各自的统计不确定度。M-15源在MCNP6蒙特卡罗环境中根据制造商提供的物理源规格进行建模。铱-192光子在M-15型号的铱芯内部均匀产生，光子和二次电子传输使用MCNP6附带的光原子截面表进行复制。对水和空气/真空计算机模型都进行了模拟，每次模拟共有4×10⁹个源光子历史，并且对空气中的光子能谱进行滤波以去除低于δ = 1 keV的低能光子。剂量学数据，包括D·(r,θ)、gL(r)、F(r,θ)、φan(r)和φ - an，以及它们的统计不确定度，是从一个MCNP模型的输出中计算得到的，该模型由放置在直径为100 cm的球形水模体中心的一个M-15源组成。自由空间中的空气比释动能强度SK和剂量率常数Λ，也从一个带有M-15铱-192源的MCNP模型中计算得到，该模型位于一个抽空模体的原点处，在距源中心100 cm处添加了一个包含标准温度和压力下空气的临界体积。参考剂量率D·(r0,θ0)≡D·(1 cm,π/2)被发现为4.038±0.064 cGy mCi⁻¹ h⁻¹。空气比释动能强度SK据报道为3.632±0.086 cGy cm² mCi⁻¹ g⁻¹，剂量率常数Λ经计算为1.112±0.029 cGy h⁻¹ U⁻¹。归一化剂量率、径向剂量函数和各向异性函数及其不确定度已计算出来，并在报告中以表格和图形形式呈现。使用MCNP6辐射传输代码对新型M-15铱-192 HDR近距离放射治疗源进行了剂量学研究。根据针对平均能量大于50 keV的近距离放射治疗源的更新后的AAPM和ESTRO剂量学参数，计算了剂量学参数，包括剂量率常数、径向剂量函数和各向异性函数。因此，这些数据可用于治疗计划程序的开发以及该源的临床应用。
