P056] Dose distribution from computed tomograghy in anthropomorphic phantom using gafchromic XR-QA2 AND TLD100H

Abstract

Purpose The Directive 2013/59/Euratom, in the transposition phase, pays particular attention to the radioprotection of the patients and therefore to the absorbed doses evaluation by diagnostic phases. In Computed Tomography (CT), this evaluation is closely linked to the CTDI calculation in homogeneous phantom. Aim of this work is to make an assessment of the dose distribution inside the organs with an anthropomorphic Rando phantom in CT, through the use of Gafchromic™XR-QA2 and TLD100H. Methods Dose mapping were obtained by using Gafchromic™XR-QA2 film and individual TLD100H dosimeters included in RANDO® Woman anthropomorphic phantom by Computed Tomography. Luminescence emissions from TLD100H, were carried out with low constant heating rate of 1 K/s and 513.15 K maximum temperature using a Riso TL/OSL-DA-10 reader. For thermoluminescence intensity evaluation a theoretical glow curve fitting, using the General-Order kinetics (GOK) expressions was applied to experimental glow curves. Gafchromic™XR-QA2 film dosimetry were digitized with Epson 10000 XL with the pixel-to-pixel veil subtraction method. For calibration curve, both for the film and for the TLD, irradiation was delivered with an X-ray tube (Samsung GC 80) in following experimental conditions: ΔV = 140 kVp, source-detector distance (SDD) = 60 cm, 10 × 10 cm2 open field. The dosimeters was placed on 30 × 30 × 10 cm3 of RW3. Calibration of the X-ray tube was done in terms of radiation output (mGy/mAs), using a Multi-Purpose Detector (MPD). Delivered doses were in the range between 0 and 100 mGy. Results A dose distribution between about 10 mGy and 30 mGy was obtained both with gafcromic film and TLDs. While in the pulmonary areas a good homogeneity of dose distribution was found. Along the sagittal sternal axis, a dose gradient was observed, especially in the area of the medulla, where dose distribution reached minimum levels. TLD and Gafchromic dose measured discrepancy was of 5% −20%. Conclusion Dose gradients found in the particular area such as the sternal/ mammary area and the medullary area are the starting point for a deepening and a critical treatment to the CDTI index until now used.