DOSIMETRIC CHARACTERIZATION OF COLLIMATORS FOR SPATIALLY FRACTIONATED PROTON THERAPY OF THE EYE.

The aim of these studies was to investigate depth dose distribution of a 60 MeV proton beam formed by a set of dedicated mesh-formed collimators. The set of mini-beams formed by the mesh is scattered in the tissue and lead to uniform energy deposition in the target volume. The rationale is to protect the eyelid skin from complications after hypofractionated radiation therapy. The experimental verification of the depth dose distribution for collimators of 1-3 mm mesh size was performed in solid state and water phantoms on 60 MeV proton beam from the AIC-144 cyclotron. The measurements were accompanied by Monte Carlo calculations of proton transport using the FLUKA code. The result demonstrate that the smallest mesh diameter of 1 mm leads to fast broadening of the resulting mini-beams due to multiple proton scattering in the collimator. The effect is diminishing with growing collimator diameter.