Room: AAPM ePoster Library
Purpose: Proof of product (POP) of a three-dimensional (3D) electronic detector array that can provide volumetric prescription dose quality assurance (QA) of an IMRT/VMAT plan within minutes after irradiation.
Methods: A 3D electronic detector array has been constructed. It consists of three concentric PMMA semi-spherical layers, 210 photodiodes in a semi-isotropic distribution and a farmer chamber in its central volume. The innermost layer has a 2 cm radius, 5 active matrices (AMs) and 3 AM pixels per matrix. Each AM pixel comprises a BPW34S photodiode, a 1 µF storage capacitor and a NX7002AK MOSFET. The central and outermost layers have radiuses of 4 cm and 6 cm, 5 active matrices (AMs) each and 12 and 27 AM pixels per matrix, respectively. A dose calibration that matched the TPS calculated dose to the voltage measured by each photodiode in a 20 x 20 cm^2 6 MV parallel-opposed SAD beams to a specific dose at isocenter, was applied to a QA measurement. Furthermore, the detector array design was converted to DICOM and exported to a TPS to be used for plan verification of a 3D conformal intracranial target treatment.
Results: Spherical coordinates were used to map the dose distribution from the calculated (TPS) and measured sources. A direct dose analysis for each diode was performed and a percent dose difference of = 4% was observed. Gamma value analysis is in progress and results are pending.
Conclusion: These preliminary results demonstrate the feasibility and mark the beginning of the development of 3D electronic detector array for IMRT/VMAT QA. The need for such a device is compelling due to advances in linac technology that have made high precision treatments routine.
Funding Support, Disclosures, and Conflict of Interest: Financial support for this project was provided by HRS Oncology International and the Universidad Nacional de Ingenieria in Lima, Peru.