Dose 2016

Origin of peripheral dose contributions Anders A .

Patient scatter

– Unavoidable – Decrease from target essentially as:

µ − ⋅

r

n =1 column shaped scatter source

e

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)!