Development of a 2D array silicon detector magic plate for the dosimetric verification of IMRT treatment delivery

Full text: We have developed an IMRT and VMAT dosimetry system for pre-treatment and during treatment verification. The 'Magic Plate' (MP) diode array was designed and prototyped by the CMRP and ICCe. It is a 2D diode array that can be used for in phantom dose measurement and can also function as a transmission detector for in vivo measurements during patient treatment. The prototype MP comprises of II x 11 silicon diodes mounted on a 0.6 mm Kapton substrate. Detectors are spaced 1 cm apart with sensitive volumes of 0.5 x 0.5 x 0.05 mm'. Phantom measurements were performed using the MP located at isocentre in the cavity of an l'mRT phantom. For fluence measurements in transmission mode the MP was mounted on the linac accessory slot. The detector was characterized and a nine field head and neck IMRT test plan was delivered. Measurements were compared with EBT2 films and Pinnacle predicted dose distributions. The 3%/3 mm gamma criteria was used for comparison. Average pass rates for the MP versus Pinnacle and MP versus EBT2 were 82.9 and 88.1 % in the phantom. Gamma analysis of MP versus EBT2 when used as transmission detectors gave a pass rate of 94.8%. The prototype MP design shows promise as IMRT dosimetric system. Future work involves refining the acquisition system, further detailed characterization, Monte Carlo simulation of the detector and its application to VMAT.