Modern Bt Techniques - Florence 2016

The Natural Dose Volume Histogram (NDVH)

Differential DVH of “ideal point source” The values of the differential DVH for an ideal point source can be calculated directly because the isodose surfaces are spheres with the source as center,

of which the volumes are easily calculated: V = (4/3) π r 3 . source with D = S / r 2 , V can be written as a function of D:

For an ideal point

V = (4/3) π S 3/2 D –3/2

Then, analytically the differential DVH for an ideal point source with D = S / r 2 is given by:

dV / dD = –2 π S 3/2 D –5/2

It is then clear that, as the dose decreases, dV / dD increases more than quadratically.