Physics in Medicine & Biology
Jun 25, 2012
Characterizing the influence of detector density on dosimeter response in non-equilibrium small photon fields
Alison J D Scott, Sudhir Kumar, Alan E Nahum and John D Fenwick 2012 Phys. Med. Biol. 57 4461
Modern radiotherapy increasingly uses photon beams with widths approaching that of the detectors used to characterise them, therefore perturbations of the dose distribution caused by the presence of non-water detectors become increasingly significant. Using Monte Carlo calculations we determined the dose that would be recorded by detectors of different sizes and compositions and compared these to the “true” dose-to-water. The ratio of the “true” dose to the dose that would be measured, Fdetector, was calculated under a wide range of conditions and shown to vary rapidly for small field sizes. By creating virtual voxels with a water-like atomic composition but a density equivalent to detector materials (silicon, diamond, air) we showed that this field-size dependent variation of Fdetector is due to the non-water-like densities of detectors, rather than differences in atomic number. Therefore ideal small-field relative dosimeters should have small active volumes and water-like density.
About the author
Alison J D Scott (Clatterbridge Centre for Oncology, Bebington, UK, and University of Liverpool, UK), Sudhir Kumar (Clatterbridge Centre for Oncology, Bebington, UK, University of Liverpool, UK, Bhabha Atomic Research Centre, Mumbai, India, and Homi Bhabha National Institute, Mumbai, India), Alan E Nahum (Clatterbridge Centre for Oncology, Bebington, UK, and University of Liverpool, UK) and John D Fenwick (Clatterbridge Centre for Oncology, Bebington, UK, University of Liverpool, UK, and University of Oxford, UK)