Mass-energy absorption coefficient and backscatter factor ratios for kilovoltage x-ray beams.
Mass-energy absorption coefficient and backscatter factor ratios for kilovoltage x-ray beams.
复制标题
千伏 X 射线束的质能吸收系数和反向散射系数比。
DOI：
10.1088/0031-9155/44/1/011
复制
发表时间：
1999
影响因子：
3.5
通讯作者：
Seuntjens,JP
中科院分区：
文献类型：
--
作者：
Ma,CM;Seuntjens,JP
对于低能量（高达150千伏）x射线，水与空气的质能吸收系数之比和后向散射系数B用于将空气中自由测量的空气克玛转换为水幻影表面上的水克玛。对于临床放射治疗，需要类似的转换因子来确定人体表面（或附近）生物组织的吸收剂量。我们计算了不同生物组织（包括肌肉、软组织、肺、皮肤和骨骼）相对于水的比率和B因子比率。比值是通过对空气中初级光子光谱的质能吸收系数进行积分得到的。我们还计算了水模体中不同深度的比值，以便将在水模体中测量到的水分转化为对各种生物组织的吸收剂量。利用EGS4/DOSIMETER蒙特卡罗编码系统，模拟了千伏x射线光束在变光束质量（HVL: 0.1 mm Al-5 mm Cu）、场大小和源面距离（SSD）下辐照水影不同深度的能量影响。同样的代码也用于计算B因子比率，软组织与水和骨骼与水。结果表明，在100场的100 kV束流（HVL: 2.65 mm Al）中，骨的B因子与水的B因子相差高达20%。另一方面，水和软组织之间B因子的差异是微不足道的（通常在1%以内）。这意味着水的B因子可以直接用于将空气中的水角质转化为人体软组织的表面角质。
For low-energy (up to 150 kV) x-rays, the ratio of mass-energy absorption coefficients for water to air,, and the backscatter factor B are used in the conversion of air kerma, measured free-in-air, to water kerma on the surface of a water phantom. For clinical radiotherapy, similar conversion factors are needed for the determination of the absorbed dose to biological tissues on (or near) the surface of a human body. We have computed the ratios and B factor ratios for different biological tissues including muscle, soft tissue, lung, skin and bone relative to water. The ratios were obtained by integrating the respective mass-energy absorption coefficients over the in-air primary photon spectra. We have also calculated the ratios at different depths in a water phantom in order to convert the measured in-phantom water kerma to the absorbed dose to various biological tissues. The EGS4/DOSIMETER Monte Carlo code system has been used for the simulation of the energy fluence at different depths in a water phantom irradiated by a kilovoltage x-ray beam of variable beam quality (HVL: 0.1 mm Al-5 mm Cu), field size and source-surface distance (SSD). The same code was also used in the calculation of the B factor ratios, soft tissue to water and bone to water. The results show that the B factor for bone differs from the B factor for water by up to 20% for a 100 kV beam (HVL: 2.65 mm Al) with a 100 field. On the other hand, the difference in the B factor between water and soft tissue is insignificant (well within 1% generally). This means that the B factors for water may be directly used to convert thein-air'water kerma to surface kerma for human soft tissues.