Three brachytherapy detectors to be compared in this paper are the following:
- Scintillation detector BrachyFOD;
- Diamond detector;
- Metal oxide semiconductor field effect transistor – MOSFET.
All of these detectors use a small active volume for accurate dosimetry (Woulfe et al. 2016). Because of small volumes, they can be calibrated using the in-air calibration technique or a solid phantom for calibration purposes. Calibration is done against national standards, which varies from one country to another. Calibration is done based on dose range, number of dose points, and calibration frequency. In emergency situations, the doses used in HDR therapy exceed 12 Gy·h-1.
Chosen detectors have their own distinct advantages and disadvantages. The diamond detector is known for having increased accuracy compared to the others, but has a larger physical size making it less usable for emergencies due to incumbrance. Thermoluminescent dosimeters do not offer real-time readings and have depth-dependent sensitivity, which is why they have been excluded from the analysis. MOSFET has the advantage of relatively decent accuracy of within 5% of error range in distances of 20 to 50 mm from the source of 192lr when used in water. However, beyond that distance, the error range increases dramatically (up to 30-40%) (Woulfe et al. 2016).
BrachyFOD is a scintillation dosimeter, which shows greater accuracy on longer distances (3% between 10-100 mm from an HDR source in water) (Woulfe et al. 2016). Its angular dependence is within 2%, while the Cerenkov radiation generates a background signal that is not significant enough to interrupt the signal generated by the scintillator (Woulfe et al. 2016). The plastic optical fiber also has a degree of fluorescence, which does not interfere with the dosimeter’s function. Out of the three compared detectors, BrachyFOD, and similar models of scintillation dosimeters, seem to have the ideal balance between size and versatility, resolution and sensitivity, energy range and accuracy, as well as linearity, in order to be used during HDR brachytherapy in the emergency rooms (Woulfe et al. 2016). Diamond detector is more cumbersome, though possessing higher accuracy, while MOSFET has a very low range, making it a suboptimal choice.
Reference List
Woulfe, P, Sullivan, FJ & O’Keeffe, S 2015, ‘Optical fibre sensors: their role in in vivo dosimetry for prostate cancer radiotherapy’, Cancer Nanotechnology, vol. 7, no. 1, pp. 7-23.