Paul J M, Koch R F, Khan F R, Devi B S
Med Phys. 1983 Mar-Apr;10(2):237-42. doi: 10.1118/1.595242.
The characteristics of 15-MV photon beam of Mevatron 77 have been examined with respect to clinical parameters. Some of the characteristics of this 15-MV photon beam are different from those of similar machines used in radiotherapy. The tissue-maximum ratio values have been determined experimentally for SAD 100 cm and percentage depth dose values have been determined from tissue-maximum ratio data. It is found that the experimentally determined PDD values for SSD 80, 100, and 120 cm are within +/- 1% of the calculated data. The scatter-maximum ratio data have been calculated from the experimentally determined zero area attenuation coefficient and tissue-maximum ratio data and are presented as function of depth and radii of circular fields. The relative dose factors have been determined both for square and rectangular fields. The relative dose factor for rectangular fields depends on the two pairs of jaws differently and the maximum difference is about 1.5%. The flatness and symmetry are within the specifications set by the manufacturer.
已针对临床参数对医用直线加速器77型的15兆伏光子束的特性进行了研究。该15兆伏光子束的一些特性与放射治疗中使用的类似机器的特性不同。已通过实验确定了源轴距（SAD）为100厘米时的组织最大剂量比数值，并根据组织最大剂量比数据确定了百分深度剂量数值。结果发现，对于源皮距（SSD）为80、100和120厘米时，实验测定的百分深度剂量（PDD）数值在计算数据的±1%范围内。散射最大剂量比数据已根据实验测定的零面积衰减系数和组织最大剂量比数据计算得出，并表示为圆形野深度和半径的函数。已确定了方形野和矩形野的相对剂量因子。矩形野的相对剂量因子对两对准直器的依赖方式不同，最大差异约为1.5%。平坦度和对称性在制造商设定的规格范围内。
