TABLE OF CONTENTS It is strongly recommended to perform a separate calibration for each radiation beam quality. If the TLDs can be identified, a calibration factor could be given to each dosimeter and it is necessary to monitor the individual factors from time to time.
In practice, having a large number of dosimeters is possible to save a part of them for the purpose of calibration. The readings of the patient dosimeters can then be converted in dose by comparing their response to the ones of the calibrated dosimeters.
The entrance dose calibration factor, F IN , is defined as the factor with which the TL signal, TL IN, of the TLD, positioned on the skin of the patient at the entrance surface, with the right built-up cap, must be multiplied to obtain the entrance dose, D IN :
F IN is determined by positioning the TLD on the surface of a flat phantom, at the entrance side of the beam. The TLD response ( TL IN) is then compared with the response of a calibrated ionization chamber ( D IN), positioned at depth d IN ,max.
The exit dose calibration factor, F OUT, is determined in a very similar way. The TLD is positioned on the exit surface of the beam and its signal is compared to the response of the calibrated ionization chamber positioned in the phantom at d OUT, max
