title: Dosimetric characteristics of a new polymer gel and their dependence on post-preparation and post-irradiation time: effect on X-ray beam profile measurements.
abstract: The aim of this study is to dosimetrically characterize a new MRI based polymer gel system and to evaluate its usefulness in clinical practice just in terms of beam profile measurements. Normoxic N-vinylpyrrolidone based polymer gel (VIPET) phantoms were produced and used in order to perform three main sets of experiments: a) dose-response evaluation and reproducibility experiments, b) experiments for the evaluation of sensitivity of dose characteristics on 'gel manufacture - irradiation' time interval and c) experiments for the evaluation of sensitivity of dose characteristics on 'irradiation - MRscanning' time interval. It has been shown that this gel system can be used in a wide dose-range of 0-60 Gy. It exhibits a linear dose-response in the dose-range of 2-35 Gy. Following the proposed manufacturing method the dose-response characteristics are reproducible. Moreover, it seems that the optimum 'gel manufacturing - irradiation' time interval is 1 day. However, a 'gel manufacturing - irradiation' time interval up to ∼1 week can be safely used. The optimum 'irradiation - MRscanning' time interval in terms of dose-response sensitivity and dose resolution can be reliably ranged from 1 day to 3 weeks. Finally, X-ray beam profile gel-measurements were performed and found to be in satisfying agreement with corresponding small sensitive volume ion chamber measurements. VIPET gel dosimeters preserved the spatial integrity of the dose distribution during a time period of 50 days post-irradiation. The studied gel system can be safely used in clinical practice within the practical limitations found and described in this work.
authors: Department of Medical Physics, MRI Unit, University of Crete, Stavrakia 71201, Crete, Greece. vasp3479@yahoo.gr
authors: Marianthi-Vasiliki
authors: MV
authors: Papoutsaki
authors: Thomas G
authors: TG
authors: Maris
authors: Evangelos
authors: E
authors: Pappas
authors: Antonios E
authors: AE
authors: Papadakis
authors: John
authors: J
authors: Damilakis
mesh_terms: D002138:Calibration; D005782:Gels; D008279:Magnetic Resonance Imaging; D019047:Phantoms, Imaging; D011205:Povidone / Q000737:chemistry*; D011874:Radiometry / Q000295:instrumentation*; D015203:Reproducibility of Results; D062211:Spatio-Temporal Analysis; D014965:X-Rays
chemical_list: D005782:Gels; D011205:Povidone
keywords: Beam profile; MRI; Normoxic polymer gel dosimetry; Radiotherapy