Calibration and Correction Factors of a Set of Semiconductor Diodes for its Use in External Radiation Therapy

摘要

The use of semiconductor diodes at the Instituto Nacional de Ciencias Medicas y Nutricion Salvador Zubiran has been essential for in-vivo dose verification of treatments in Radiation Therapy. Three types of semiconductor diodes, two for photons of low (6 and 10 MV) and high (15 MV) energies; one for electron beams were characterized. The entrance and exit calibration factors for photons and the entrance calibration factors for electrons were obtained under standard conditions in a phantom of solid water using cylindrical and plane parallel ionization chambers for photons and electrons, respectively. Also, the signal diode as a function of monitor units and the angular dependence for photon and electron beams were analyzed; and the source surface distance and field size dependences for photons were determined. The results show that the signal is linear with monitor units and depends on beam quality, increases as a function of angle of incidence and field size and decreases with source surface distance.