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

Abstract

Aim

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

Background

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.

Materials and methods

In this study we used a 30[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]30[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]25[[ce:hsp sp="0.25"/]]cm PMMA slab phantom. On the surface of the phantom, various semiconductor detectors were placed sequentially in two configurations, angle and tilt.

Results

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[[ce:hsp sp="0.25"/]]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[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]8[[ce:hsp sp="0.25"/]]cm and 10[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]10[[ce:hsp sp="0.25"/]]cm. With the increase field size, the correction factor shows a linear relationship in the direction of value less than 1.00.

Conclusion

Flat Detectors – used for both photon beams generated by the accelerating potential of 6[[ce:hsp sp="0.25"/]]MV and 20[[ce:hsp sp="0.25"/]]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.