[用蒙特卡罗方法模拟I光子发射源在骨介质中的剂量分布]

[Simulation of dose distribution in bone medium of I photon emitting source with Monte Carlo method].

作者信息

Ye K Q, Huang M W, Li J L, Tang J T, Zhang J G

机构信息

Department of Oral and Maxillofacial Surgery, Peking University School and Hospital of Stomatology & National Engineering Laboratory for Digital and Material Technology of Stomatology & Beijing Key Laboratory of Digital Stomatology, Beijing 100081, China.

Department of Engineering Physics, Tsinghua University, Key Laboratory of Particle and Radiation Imaging, Ministry of Education, Key Laboratory of High Energy Radiation Imaging Fundamental Science,Beijing 100084, China.

出版信息

Beijing Da Xue Xue Bao Yi Xue Ban. 2018 Feb 18;50(1):131-135.

PMID:29483735

Abstract

OBJECTIVE

To present a theoretical analysis of how the presence of bone in interstitial brachytherapy affects dose rate distributions with MCNP4C Monte Carlo code and to prepare for the next clinical study on the dose distribution of interstitial brachytherapy in head and neck neoplasm.

METHODS

Type 6711,I brachytherapy source was simulated with MCNP4C Monte Carlo code whose cross section library was DLC-200. The dose distribution along the transverse axis in water and dose constant were compared with the American Association of Physicists in Medicine (AAPM) TG43UI update dosimetry formalism and current literature. The validated computer code was then applied to simple homogeneous bone tissue model to determine the affected different bone tissue had on dose distribution from I interstitial implant.

RESULTS

I brachytherapy source simulated with MCNP4C Monte Carlo code met the requirements of TG43UI report. Dose rate constant, 0.977 78 cGy/(h×U), was in agreement within 1.32% compared with the recommended value of TG43UI. There was a good agreement between TG43UI about the dosimetric parameters at distances of 1 to 10 cm along the transverse axis of the I source established by MCNP4C and current published data. And the dose distribution of I photon emitting source in different bone tissue was calculated. Dose-deposition capacity of photons was in decreasing order: cortical bone, spongy bone, cartilage, yellow bone marrow, red bone marrow in the same medium depth. Photons deposited significantly in traversal axis among the phantom material of cortical bone and sponge bone relevant to the dose to water. In the medium depth of 0.01 cm, 0.1 cm, and 1 cm, the dose in the cortical bone was 12.90 times, 9.72 times, and 0.30 times of water respectively.

CONCLUSION

This study build a I source model with MCNP4C Monte Carlo code, which is validated, and could be used in subsequent study. Dose distribution of photons in different bone medium is not the same as water, and its main energy deposits in bone medium surface, so we should consider the effect of bone medium when we design the target area adjacent to the bone tissue in I sources implantation plan.

摘要

目的

运用MCNP4C蒙特卡罗代码对组织间近距离治疗中骨的存在如何影响剂量率分布进行理论分析，为后续头颈部肿瘤组织间近距离治疗剂量分布的临床研究做准备。

方法

用MCNP4C蒙特卡罗代码模拟6711型I近距离治疗源，其截面库为DLC - 200。将水模中沿横轴的剂量分布和剂量常数与美国医学物理师协会（AAPM）TG43UI更新后的剂量学形式主义及当前文献进行比较。然后将经验证的计算机代码应用于简单的均匀骨组织模型，以确定不同骨组织对I组织间植入剂量分布的影响。

结果

用MCNP4C蒙特卡罗代码模拟的I近距离治疗源符合TG43UI报告的要求。剂量率常数为0.97778 cGy/(h×U)，与TG43UI推荐值相比，在1.32%的范围内一致。MCNP4C在I源横轴1至10 cm距离处建立的剂量学参数与TG43UI及当前已发表数据之间有良好的一致性。并且计算了I光子发射源在不同骨组织中的剂量分布。在相同介质深度下，光子的剂量沉积能力顺序为：皮质骨、松质骨、软骨、黄骨髓、红骨髓。与水的剂量相关，光子在穿过皮质骨和松质骨的体模材料时，在横轴上有显著沉积。在0.01 cm、0.1 cm和1 cm的介质深度处，皮质骨中的剂量分别是水的12.90倍、9.72倍和0.30倍。