4 research outputs found
Recommended from our members
Lowâcost flexible thinâfilm detector for medical dosimetry applications
The purpose of this study is to characterize dosimetric properties of thin film photovoltaic sensors as a platform for development of prototype dose verification equipment in radiotherapy. Towards this goal, flexible thinâfilm sensors of dose with embedded data acquisition electronics and wireless data transmission are prototyped and tested in kV and MV photon beams. Fundamental dosimetric properties are determined in view of a specific application to dose verification in multiple planes or curved surfaces inside a phantom. Uniqueness of the new thinâfilm sensors consists in their mechanical properties, lowâpower operation, and lowâcost. They are thinner and more flexible than dosimetric films. In principle, each thinâfilm sensor can be fabricated in any size (mm2 â cm2 areas) and shape. Individual sensors can be put together in an array of sensors spreading over large areas and yet being light. Photovoltaic mode of charge collection (of electrons and holes) does not require external electric field applied to the sensor, and this implies simplicity of data acquisition electronics and low power operation. The prototype device use for testing consists of several thin film dose sensors, each of about 1.5 cmĂ5 cm area, connected to simple readout electronics. Sensitivity of the sensors is determined per unit area and compared to EPID sensitivity, as well as other standard photodiodes. Each sensor independently measures dose and is based on commercially available flexible thinâfilm aSi photodiodes. Readout electronics consists of an ultra lowâpower microcontroller, radio frequency transmitter, and a lowânoise amplification circuit implemented on a flexible printed circuit board. Detector output is digitized and transmitted wirelessly to an external host computer where it is integrated and processed. A megavoltage medical linear accelerator (Varian Tx) equipped with kilovoltage online imaging system and a Cobalt source are use to irradiate different thinâfilm detector sensors in a Solid Water phantom under various irradiation conditions. Different factors are considered in characterization of the device attributes: energies (80 kVp, 130 kVp, 6 MV, 15 MV), dose rates (different ms Ă mA, 100â600 MU/min), total doses (0.1 cGyâ500 cGy), depths (0.5 cmâ20 cm), irradiation angles with respect to the detector surface (0°â180°), and IMRT tests (closed MLC, sweeping gap). The detector response to MV radiation is both linear with total dose (~1â400 cGy) and independent of dose rate (100â600 Mu/min). The sensitivity per unit area of thinâfilm sensors is lower than for aSi flatâpanel detectors, but sufficient to acquire stable and accurate signals during irradiations. The proposed thinâfilm photodiode system has properties which make it promising for clinical dosimetry. Due to the mechanical flexibility of each sensor and readout electronics, lowâcost, and wireless data acquisition, it could be considered for quality assurance (e.g., IMRT, mechanical linac QA), as well as realâtime dose monitoring in challenging setup configurations, including large area and 3D detection (multiple planes or curved surfaces). PACS number: 87.56.F