Table 2. Relative risks for malignant induction (protons vs X-rays), as defined in Equation 8, for a centrally located planning target volume with 10% beam penumbra treated by one, two opposed (2 op), two orthogonal (2 or), three-field or four-field plans. Values greater than unity mean that protons have higher malignant induction probability than X-rays.

	Protons
X-rays	1	2 op	2 or	3	4
1	0.69	1.92	1.77	2.85	3.54
2 op	0.86	2.38	2.19	3.54	4.40
2 or	0.40	1.11	1.02	1.65	2.05
3	0.44	1.22	1.12	1.81	2.25
4	0.62	1.73	1.60	2.58	3.20