Reproducibility is the biggest difference when comparing systems. As seen in the chart, which uses information from the manufacturer’s literature, the MOSFET detectors are much less reproducible than an ISORAD™ or QED™ diode detector. Reproducibility is defined as the percentage difference between consecutive measurements for the same radiation dose under the same conditions. The data in the following table was at 1 σ (32% of the readings will have worse reproducibility). If the reproducibility is calculated at 3 σ, it will be much worse for MOSFET detectors, but the same for Isorad and QED diodes. 

Furthermore, certain MOSFET characteristics are voided if the detector is used for dmax measurements, which is usually the method of choice. For MOSFETs, buildup must be added in different amounts depending on energy to provide a reading at dmax. (DIODES do not require this.) Once buildup is added to a MOSFET, certain advantages, such as low attenuation, low energy dependence, and “one” detector for multiple energies evaporate.

It is important to note that the QED and ISORAD-3™ detector is available without buildup if so desired. Also, the ISORAD-3™ is isotropic, meaning it can be irradiated from any angle along the x-axis with less than a 1% variation in response.

The MOSFETs also suffer from a very short lifetime, creep-up effect, signal fading, and a lack of real time reading.


Comparative Table