Prasad S C, Bassano D A, Ames T E
Med Phys. 1984 Mar-Apr;11(2):204-6. doi: 10.1118/1.595602.
Accuracy of dose calculation for regular fields in off-central axis planes was investigated on a RAD-8 treatment planning computer for 4- and 10-MV x-ray beams produced by Varian Clinac -4 and Clinac -18 linear accelerators. These calculations, which are based on central axis depth dose and off-axis ratios in the principal planes, can be in error by as much as 25%-30% at locations well within the irradiated volume for the 4-MV x-ray beam. These large errors for the Clinac -4 beam result from the falloff in dose beyond the peak dose along a diagonal of a large field at distances greater than 14 cm from the central axis due to the lead flattening filter. The profile data stored in the computer along the principal planes cannot be used to calculate the dose accurately in such a situation. Computed doses for the 10-MV x-ray beam agreed with the measured doses within 4%-6% at all locations.
在一台RAD - 8治疗计划计算机上，针对Varian Clinac - 4和Clinac - 18直线加速器产生的4兆伏和10兆伏X射线束，研究了离轴平面中规则射野剂量计算的准确性。这些基于中心轴深度剂量和主平面离轴比的计算，对于4兆伏X射线束，在照射野内的位置处误差可能高达25% - 30%。Clinac - 4射线束出现这些大误差是由于铅扁平滤过器导致在距中心轴大于14厘米处，大射野对角线上剂量在峰值剂量之外出现下降。在这种情况下，计算机中沿主平面存储的轮廓数据无法用于准确计算剂量。对于10兆伏X射线束，在所有位置计算得到的剂量与测量剂量的偏差在4% - 6%以内。
