ESTRO course Dose Modelling and Verification 2017

The physics of small MV photon fields

The conditions that determine whether a field is classified as small are:

1. Loss of lateral charged particle equilibrium (CPE)

2. Partial occlusion of the primary photon source by the collimating device

3. The detector perturbs particle fluence because of its size (too large in

comparison to the field size) and/or its composition