Characterization of a novel two dimensional diode array the “magic plate” as a radiation detector for radiation therapy treatment

• Published in: Medical physics (Lancaster) 2012-05, Vol.39 (5), p.2544-2558
• Main Authors: Wong, J. H. D., Fuduli, I., Carolan, M., Petasecca, M., Lerch, M. L. F., Perevertaylo, V. L., Metcalfe, P., Rosenfeld, A. B.
• Format: Article
• Language: English
• Subjects: 2D diode array; Air; biomedical equipment; COLLIMATORS; DEPTH DOSE DISTRIBUTIONS; DOSE RATES; DOSEMETERS; dosimeters; dosimetry; Dosimetry/exposure assessment; Epitaxy; Field size; FILM DOSIMETRY; IMRT; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; IONIZATION CHAMBERS; Junction diodes; Linear accelerators; Linear Models; magic plate; Measurement of nuclear or x‐radiation; Multileaf collimators; PERTURBATION THEORY; PHANTOMS; Phantoms, Imaging; Photons; PHYSICAL RADIATION EFFECTS; Radiation detectors; RADIATION DOSES; radiation therapy; RADIOLOGY AND NUCLEAR MEDICINE; Radiometry - instrumentation; RADIOTHERAPY; Radiotherapy Dosage; Radiotherapy, Computer-Assisted - adverse effects; Radiotherapy, Computer-Assisted - instrumentation; semiconductor counters; SEMICONDUCTOR DETECTORS; Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having at least one potential‐jump barrier or surface barrier; Capacitors or resistors with at least one potential‐jump barrier or surface barrier, e.g. pn‐junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof; semiconductor diodes; SI SEMICONDUCTOR DETECTORS; Silicon; Silicon detectors; SILICON DIODES; Solid‐state detectors; Surface Properties; SURFACES; Therapeutic applications, including brachytherapy; transmission detector; Tubes for determining the presence, intensity, density or energy of radiation or particles; TWO-DIMENSIONAL CALCULATIONS; Water
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.3700234

Purpose: Intensity modulated radiation therapy (IMRT) utilizes the technology of multileaf collimators to deliver highly modulated and complex radiation treatment. Dosimetric verification of the IMRT treatment requires the verification of the delivered dose distribution. Two dimensional ion chamber or diode arrays are gaining popularity as a dosimeter of choice due to their real time feedback compared to film dosimetry. This paper describes the characterization of a novel 2D diode array, which has been named the “magic plate” (MP). It was designed to function as a 2D transmission detector as well as a planar detector for dose distribution measurements in a solid water phantom for the dosimetric verification of IMRT treatment delivery. Methods: The prototype MP is an 11 × 11 detector array based on thin (50μm) epitaxial diode technology mounted on a 0.6 mm thick Kapton substrate using a proprietary “drop-in” technology developed by the Centre for Medical Radiation Physics, University of Wollongong. A full characterization of the detector was performed, including radiation damage study, dose per pulse effect, percent depth dose comparison with CC13 ion chamber and build up characteristics with a parallel plane ion chamber measurements, dose linearity, energy response and angular response. Results: Postirradiated magic plate diodes showed a reproducibility of 2.1%. The MP dose per pulse response decreased at higher dose rates while at lower dose rates the MP appears to be dose rate independent. The depth dose measurement of the MP agrees with ion chamber depth dose measurements to within 0.7% while dose linearity was excellent. MP showed angular response dependency due to the anisotropy of the silicon diode with the maximum variation in angular response of 10.8% at gantry angle 180°. Angular dependence was within 3.5% for the gantry angles ± 75°. The field size dependence of the MP at isocenter agrees with ion chamber measurement to within 1.1%. In the beam perturbation study, the surface dose increased by 12.1% for a 30 × 30 cm2 field size at the source to detector distance (SDD) of 80 cm whilst the transmission for the MP was 99%. Conclusions: The radiation response of the magic plate was successfully characterized. The array of epitaxial silicon based detectors with “drop-in” packaging showed properties suitable to be used as a simplified multipurpose and nonperturbing 2D radiation detector for radiation therapy dosimetric verification.