ESTRO course Dose Modelling and Verification 2017

Origin of peripheral dose contributions Anders A .

Patient scatter

– Unavoidable – Decrease from target essentially as:

r

  

e

n =1 column shaped scatter source n =2 “blob” shaped scatter source

n r

Head scatter 

Sources are all irradiated parts of the treatment head, main source the flattening filter  Limited by the collimating devices  Machine design dependent (FFF machines have less!)

Leakage, including scatter leakage 

Depends on collimator and shield thicknesses and material (density)  Collimator design dependent  Treatment technique dependent

Neutrons 

Mainly a high Z phenomena at photon energies above photonuclear threshold values  Avoidable by lower beam energy

Only one factor user controllable on a daily basis, all other once per decade (replacement)!