Contribution to optimizing in vivo measurements using semiconductor detectors

Despite the important growth in the power of computers, incomplete software development means that it is not always possible to have available beforehand dosimetric information for some treatment protocols. Real-time irradiation monitoring, dose control and dose assessment for some parts of the anatomy can be carried out only by making supplementary use of in vivo detectors. The study evaluates semiconductor detectors exposed to beams of electrons at 7 to 22 MeV and to 25 MV photons from a linear accelerator, and is in two parts: an experimental study of the sensor characteristics as affected by the size of the received dose, dose rate, energy, incidence of the beam and temperature; and an in vivo study of their use in treatment protocols, with the modelling done beforehand or correlation effected with the results from other measurement or calculation techniques. The experimental study on the 'electron' sensors showed that these detectors were rather anisotropic, with a major loss of signal on tangential irradiation; certain irradiation positions must be corrected for in order to make these detectors acceptable in use. They are temperature-sensitive and their response is energy-dependent, and corrections must therefore be made as necessary. The 'photon' detectors give a nominal response to within about 2% when inside a cone with an angle of less than 60 deg.; otherwise, the response increases to as much as +8%, which is a major drawback given the degree of precision required. Nevertheless, the attractive features of these detectors and their high performance in the other parameters studied make it evident that these sensors are useful in carrying out the treatment plan in the proper manner. This point of view is further developed. (author). 10 refs