IMRT 2017

By collimating a beam from a source of finite width, it is clear that below a certain field size, only a part of the source area can be viewed from a detector’s point of view. The output will then be lower than compared to field sizes at which the entire source can be viewed from the detector’s field of view. IMRT CONCERNS ON SMALL FIELD DOSIMETRY AND BEAM MODELLING

complete view of the source • absorbed dose from primary radiation fully received • penumbra defined from source perimeter to collimating edges without overlapping

partial blocking of the source • absorbed dose reduction from primary radiation • penumbra overlapping from opposing collimating edges

( Aspradakis et al ., Med Dosim. 2005 )