SBRT2015

Dosimetry of Small Fields



Measurement of small photon beams is complicated by



loss of lateral electronic equilibrium,



volume averaging,



detector-interface artifacts,



collimator effects,



and detector position-orientation effects



Recommendation: use an appropriate dosimeter with a spatial resolution of

approximately 1 mm or better (stereotactic detectors)



Collimator with a diameter of 5 mm => dose falloff over a radius of 2.5 mm



Thickness of 1 euro coin is 2.3 mm!