The Study of Field Equivalence Determined by the Modeled Percentage Depth Dose in Electron Beam Radiation Therapy

Table 4

The comparison ofand, the minimum side lengths to remain the standard percent depth doses of 9 MeV and 15 MeV unchanged are 4.9 cm and 5.9 cm, respectively.

Energy (MeV) (nominal)	(MeV)			Slope (80%-20%)	tan^-1 (slope)			(mm, this study)	(mm)
6	5.41	90	3.1	-8.6593	-1.45582	0.001	-6.9077	38.13	36.75
9	8.66	210	6.2	-5.7176	-1.39765	0.0007	-7.2644	49.17	46.50
12	11.27	290	8.9	-4.5559	-1.35473	0.0005	-7.6009	53.98	53.04
15	14.04	400	12.3	-3.3749	-1.28273	0.0003	-8.1117	59.33	59.20
18	17.03	470	15.1	-2.6474	-1.20964	0.0002	-8.5171	62.10	65.20