Notes on the construction of solid-state detectors.

BACKGROUND AND PURPOSE Solid-state detectors such as diodes and diamonds are useful radiation detectors, particularly for small field measurements, such as in stereotactic dosimetry or in the small sub-field measurements required for intensity modulated radiotherapy (IMRT) . In all small field measurements, positioning of the detector is critical. Generally it is assumed that the center of the sensitive volume of each solid-state detector is coincident with the geometric center of the outer casing. PATIENTS AND METHODS X-rays were taken of four detectors (diamond, three types of diode) to determine the physical characteristics of each, particularly the position of the centre of the sensitive volume. RESULTS The results showed that the position of the centre of the sensitive volume is not always coincident with the geometric centre of a solid-state detector. CONCLUSIONS The construction of a detector used for precise measurements should be investigated prior to use, by taking high resolution x-ray images.