Dependency of semiconductor dosimeter responses, used in MDR/LDR brachytherapy, on factors which are important in clinical conditions

Abstract

Aim

Dependence of diode dosimeters on variation of temperature, distance, dose rate and incident beam angle for MDR/LDR intracavitary brachytherapy was investigated.

Materials/Methods

Flexible probes from PTW/Germany were irradiated using Cs-137 sources. The rectum probe (type 9112) had five semiconductors and the bladder probe had one. Firstly, detectors' dependence on temperature was studied. The probes were immersed into a water tank and the temperature was slowly increased. To investigate the angular dependence of the diodes, the sources were placed at 5cm distance from diodes at four different angles. Probes were placed at 3cm distance from the centre of the source arrays and the responses for three different dose rates were evaluated. To assess the dependency of responses on distance, probes were placed at three different distances with constant dose rate.

Results

A slight linear increase of the diode signal with temperature was found. The diodes exhibited a variation in sensitivity with dose rate less than 0.15% and with distance less than 0.04% per mm. A linear decrease of the diode responses was also observed with increase of the radiation beam angle.

Conclusions

The current study showed that there is no significant variation in the response of diodes with temperature, dose rate and distance for MDR brachytherapy. However, the increase of radiation beam angle led to a significant decrease of diode response. In conclusion, the observed temperature, dose rate and distance effects are negligible but the diode correction factor as a function of the incidence beam angle must be applied to these diodes.