Chen F S
Department of Radiation Oncology, Saint John Regional Hospital, New Brunswick, Canada.
Med Phys. 1988 May-Jun;15(3):348-50. doi: 10.1118/1.596229.
A polynomial formula, deduced from the data published by Mills et al. [Med. Phys. 12, 473 (1985)], in predicting the relative electron beam output factors, is presented in this report. This formula contains four parameters. By choosing four measured output factors, from four field sizes normalized at the field size of (10,10), the values of these parameters can be determined. A comparison of the factors predicted with this formula and the values measured by Mills et al. shows that the differences between the field sizes of (4,4) to (30,30) are 0.5% or less in 31 out of 35 field sizes. All the 35 field sizes are within 1% for an electron beam of 20 MeV. With 6-MeV electron beams, the differences are 0.5% or less in 26 out of 35 field sizes, and 1% or less in 31 out of 35 field sizes. Those having differences greater than 1% have either a small field size (5 cm) or a large field size (20 cm). Considering that this formula requires only four accurately measured relative output factors, one can predict the factors of any field within an acceptable accuracy. The calculation is easy with a scientific hand calculator. This formula provides major improvement over the other methods which require many measurements to be taken in order to interpolate with acceptable accuracy.
本报告给出了一个根据米尔斯等人[《医学物理》12, 473 (1985)]发表的数据推导出来的用于预测相对电子束输出因子的多项式公式。该公式包含四个参数。通过选择在(10,10)场尺寸下归一化的四个场尺寸的四个测量输出因子，可以确定这些参数的值。将用此公式预测的因子与米尔斯等人测量的值进行比较表明，在35个场尺寸中的31个中，(4,4)至(30,30)场尺寸之间的差异为0.5%或更小。对于20 MeV的电子束，所有35个场尺寸的差异都在1%以内。对于6 MeV的电子束，35个场尺寸中的26个差异为0.5%或更小，35个场尺寸中的31个差异为1%或更小。差异大于1%的情况要么是小场尺寸(5 cm)，要么是大场尺寸(20 cm)。考虑到该公式只需要四个精确测量的相对输出因子，就可以在可接受的精度内预测任何场的因子。用科学计算器计算很容易。与其他需要进行许多测量才能以可接受的精度进行插值的方法相比，这个公式有了很大的改进。
