Measurement of conversion coefficients beteen free-in-air kerma and personal dose equivalent for RQR spectra to be used in monitoring of the eye lens in nterventional radiology

Abstract

Introduction The recommended operational quantity to monitor eye lens exposure in interventional radiology is personal dose equivalent in 3 mm depth: H p (3). However, there are no conversion coefficients suggested in international standards. Purpose The aim of this study was to calculate the air kerma (K a ) to H p (3) conversion coefficients for a cylindrical phantom based on measurements with the radiation qualities RQR2 to RQR10 that provide better approximation of X-ray spectra used in interventional radiology, especially compared to narrow spectra applied for calibration of personal dosemeters. Materials and methods The conversion coefficients h p,k (3) were determined using the formula h p , k ( 3 ) = H p ( 3 ) K a = μ en ρ air mat BSF · PDD The backscatter factors, BSF, were measured using LiF:Mn,Ti thermoluminescent detectors on a homogeneous cylindrical phantom and free in air kerma. RQRs radiation qualities were reproduced in the Secondary Standards Dosimetry Laboratory – Sofia, Bulgaria. Data for dry air and ICRU soft tissue were taken from NIST. Results The Percentage Depth Dose, PDD, for RQR2 to RQR10 were calculated, BSFs were measured and conversion coefficients h pK (3, RQR,0°) were determined for the new cylindrical phantom. The results are in good agreement with those published by Principi et all. Conclusions The conversion coefficients from the air kerma (K a ) to H p (3) for radiation qualities RQR 2 to RQR 10 can be used in occupational dosimetry for interventional radiology.