Calculation of conversion factor relating measured patient entrance skin dose and scanner registered computed tomography dose index during sinus examination

Abstract

Introduction Radiochromic films (RF) have successfully been used in measuring radiation doses in computed tomography (CT). The films were reported to have the ability to picture radiation dose profile, to measure entrance surface dose (ESD), and the peak surface dose (PSD). Purpose The objective of this work was to study the feasibility of using RF as in vivo dosimeters to measure ESD from patients undergoing routine CT examination of the sinus and relate the measurements to the scanner calculated computed tomography dose index ( CTDI vol ) available at the scanner console. Materials and methods Gafchromic XR-QA2 film strips were calibrated against the reading from a 300 mm long pencil type ionization chamber calibrated in terms of CT dose length product (DLP). The in vivo measured ESD and PSD from 12 patients using films were used to calculate the conversion factors: C S = ESD / CTDI vol and C PK = PSD / CTDI vol . Results The calculated conversion coefficients C S and C pk were 0.88 and 1.18 respectively. The films were easily and effectively implemented as In-vivo dosimeter during CT imaging of the sinus allowing for a more accurate estimate of typical surface doses found in CT imaging. Conclusion The films had the advantage of not interfering with the patient setup and did not produce any image artifacts. The method can be used to study other CT examinations specially the ones with larger beam width and high pitch factor, to predict the peak skin dose, to examine the CT dose profile and the radiation dose distribution during annual QA. Disclosure we have nothing to disclose in relation with the presented work.