Verification of the Accuracy of the Delivered Dose in Brain Tumors by in Vivo Dosimetry Using Diode Detectors

Introduction: During radiotherapy, high accuracy in the dose delivery is required because there is a strong  relationship between the absorbed dose, local tumor control and particularly the normal tissue damage. In  many institutions, in vivo dosimetry using diodes is performed to check the actual dose delivered. In general,  the uncertainty in the dose delivered should fall within  ± 5% of the prescribed dose as recommended by the  International Commission on Radiation Units and Measurements (ICRU).  Materials and Methods: The combined entrance and exit dose measurements have been performed for brain  tumors by diode detectors. In vivo detectors used in this study were P-type semiconductor diodes used for  determination of absorbed dose and exit transmission (T ex ). A Perspex water phantom (30×30 cm3 area and  thickness  ranging  from  5  to  30  cm)  and  a  farmer  type  ionization  chamber  (0.6  cm3)  were  used  for  the  measurements.  The  calibration  and  correction  factor  are  calculated  and  the  relevant  curves  have  been  obtained. The SSD correction factor (SSD = 80 cm for all set-up), directional dependence and temperature  dependence (0.1) was observed.  Discussion and Conclusion: In vivo measurements have been shown to be very useful as a check of the dose  delivered to a given patient.