Relationship of the risk of RILD to the nominal diameter of GTV. Prescribed doses of 60 Gy for IMRT (black diamond) and 60GyE for SSPT (open circle), delivered in 15 fractions, were normalized for all plans to 1.5 Gy b.i.d. assuming an α/β of 2.5, based on the LKB-NTCP model (n = 0.97, m = 0.12, TD
(1) = 39.8 Gy ). The difference of the risk of RILD between IMRT and SSPT plans clearly increased from 6–7 cm nominal diameter of GTV.