IMRT

Lyman model (1985, Rad Res 104, 13-19) Basic assumptions : • Dose dependence : cumulative normal distribution resulting in a sigmoid-shape dose response curve (error function)/dose-NTCP plane

t ∫

2 1

(

) dt t 2/ 2

exp

NTCP

=

−

π

∞−

)( * )( vDm vDD t

−

=

50

50

• Volume dependence : power law relationship for tolerance doses/dose-volume plane

( ) n v vD D *

)1(

=

Parameters : D 50 dose to the whole organ giving 50% NTCP m steepness (variation in radiosensitivity across patient population) n volume exponent (volume effect : n=1 large, n=0 small) (n descríbes the magnitude of the volume effect)

50

50

extension to non-uniform irradiation through an algorithm (“DHV reduction”) LKB model Parameters for 28 complications: Burman et al, IJROBP 21, 123 (1991)