Wang R, Li X A
Department of Radiation Oncology, University of Maryland, Baltimore 21201, USA.
Med Phys. 2001 Feb;28(2):134-41. doi: 10.1118/1.1339880.
The dose parameters for the beta-particle emitting 90Sr/90Y source for intravascular brachytherapy (IVBT) have been calculated by different investigators. At a distant distance from the source, noticeable differences are seen in these parameters calculated using different Monte Carlo codes. The purpose of this work is to quantify as well as to understand these differences. We have compared a series of calculations using an EGS4, an EGSnrc, and the MCNP Monte Carlo codes. Data calculated and compared include the depth dose curve for a broad parallel beam of electrons, and radial dose distributions for point electron sources (monoenergetic or polyenergetic) and for a real 90Sr/90Y source. For the 90Sr/90Y source, the doses at the reference position (2 mm radial distance) calculated by the three code agree within 2%. However, the differences between the dose calculated by the three codes can be over 20% in the radial distance range interested in IVBT. The difference increases with radial distance from source, and reaches 30% at the tail of dose curve. These differences may be partially attributed to the different multiple scattering theories and Monte Carlo models for electron transport adopted in these three codes. Doses calculated by the EGSnrc code are more accurate than those by the EGS4. The two calculations agree within 5% for radial distance <6 mm.
不同研究人员已对用于血管内近距离放射治疗（IVBT）的发射β粒子的90Sr/90Y源的剂量参数进行了计算。在距源较远的距离处，使用不同蒙特卡罗代码计算出的这些参数存在明显差异。这项工作的目的是量化并理解这些差异。我们比较了使用EGS4、EGSnrc和MCNP蒙特卡罗代码进行的一系列计算。计算和比较的数据包括宽平行电子束的深度剂量曲线，以及点电子源（单能或多能）和真实90Sr/90Y源的径向剂量分布。对于90Sr/90Y源，由这三种代码计算出的参考位置（径向距离2mm）处的剂量在2%以内相符。然而，在IVBT感兴趣的径向距离范围内，这三种代码计算出的剂量之间的差异可能超过20%。差异随着距源径向距离的增加而增大，在剂量曲线尾部达到30%。这些差异可能部分归因于这三种代码中采用的不同多重散射理论和电子输运蒙特卡罗模型。由EGSnrc代码计算出的剂量比由EGS4计算出的更准确。对于径向距离<6mm，这两种计算结果在5%以内相符。
