The semiconductor diode detector response as a function of field size and beam angle of high-energy photons

The measurements of semiconductor diode detector response as a function of field size and beam angle of high-energy photons.

In vivo dosimetry plays an important role in the therapeutic process of the patient. Because of the different orientation of the beam relative to the patient and different sizes of irradiation fields, it is extremely important to take into account the response of the detector depending on the angle and the size of the beam.

In this study we used a 30 cm × 30 cm × 25 cm PMMA slab phantom. On the surface of the phantom, various semiconductor detectors were placed sequentially in two configurations, angle and tilt.

For the measurements of the calibration factor based on the different value of the angle, the correction coefficient value was close to 1.00 for smaller values of the angle for all the detectors used in the energy range of 6-12 MV. For the measurements, the calibration factor based on the size of the field of irradiation to the value of the correction coefficient is 1.00 for the field of 8 cm × 8 cm and 10 cm × 10 cm. With the increase field size, the correction factor shows a linear relationship in the direction of value less than 1.00.

Flat Detectors - used for both photon beams generated by the accelerating potential of 6 MV and 20 MV show a greater angular dependence than the cylindrical detectors. Also, the repeatability of measurements made using the flat detector is less as evidenced by larger standard deviations for the results.