Page 49 - Fisica In Medicina n° 1/2017

^Äëíê~Åí=cáëáÅá= =TPRs and OCRs beam data, measured using the diode detector, are in good agreement with multi- site data provided by Accuray (Δmax<2%), for both the collimation systems. The greatest discrepancy between measured and the averaged data occurred for TPRs surface measurement where the dependence by thedetector and set-up becomessignificant. OCRsmeasurement of the smallestaperture of fixed collimator,repeated with the diamonddetector, generate a slightly higher signal in the penumbra region because of a greater volume averaging effect (r=1.1mm).OFs measured with the diode were found to be in good agreement with multi-site data (Δ<0,1% for φ ≥10 mm and Δmax<1.7% for φ =5mm). Diode OFs values, corrected by Monte Carlo factors, and raw diamond OFs values are in agreement within 1,2%.ConclusionThe high agreement between measured diode and multi-site data leads to consider the diode as an ideal detector for stereotactic radiation fields. Moreover the negligible deviation between corrected diode and raw diamond OFs confirm the latter as a free correction detector, very useful too in small field dosimetry.Figure 1. OCRs, TPRs and OFs comparisons40