بررسي تاثير ميدان الكتريكي خارجي بر دوز جذبي ناشي از اشعه كبالت 60

Evaluation of external electric field on the absorbed dose of cobalt 60 radiation

Objective: Localizing of radiation onto tumor volume is important in limits damage due to secondary radiation to surrounding normal tissues. The aim of the present study was to assess the effects of external electrical field on the absorbed secondary radiation using water phantom technique. Material and Methods: A water phantom (20x20x10 cm3) was positioned in an electric field with different intensity from 11.25 kV/m to 90 kV, dosimetry was measured at 5 cm of depth for treatment fields with 5x5 cm2 to 20 x20 cm2 and SSD(source - skin- distance) =80 cm with y radiation with cobalt 60. for estimating the enhancement of absorbed does due to the parameter of DER(Dose enhancement Reading of dosimeter in the presence of electric ratio) as the form DER=-----xl00 Reading of dosimeter in the absemco of electric feild Defined and calculated. Results: Variation of DER with respect to dimension of treatment fields and intensity of electric field showed that applying of electric field on radiation field caused the increment of absorbed dose and DER. With increasing rate between 5% -10% for fields 5x5 cm2 up 2 20x 20 cm2 in 90 kv/m intensity of electric field Conclusion: It seems that applying the electric field on water phantom in deferent photon fields prevent from recombination of produced ions in water phantom and caused 5% -10% enhancement in absorbed dose by transmitting more energy in the medium by this ions.