A three-dimensional electronic detector array for radiotherapy based on active matrices

A three-dimensional electronic detector array consisting of an active matrix readout configuration has been designed. The array comprises 31,560 submillimeter size photodiodes isotropically distributed within a 20 cm diameter semi-spherical volume of water equivalent material. The number of photodiodes in an active matrix varies from 27 to 972, and 80 active matrices with 4200 channels are connected to a data acquisition unit for readout. A low resolution 20 cm diameter semi-spherical electronic detector array was constructed to test the active matrix readout configuration response. The array consists of 135 BPW34S photodiodes distributed in a 12 cm diameter layer and one ionization chamber at the center of the semi-spherical volume. Furthermore, a quality assurance plan for a 6-field 6-MV intracranial treatment was generated to check the array’s response. The array was dose calibrated using 20 x 20 cm² parallel-opposed 6 MV photon beams from a Varian 2100 C/D linear accelerator and the integrated voltage from each photodiode was matched to the calculated dose from a treatment planning software for that photodiode location. Data analysis resulted in a percent dose difference between the measured and calculated dose of = 5%.