title: MAGIC-type polymer gel for three-dimensional dosimetry: intensity-modulated radiation therapy verification.
abstract: A new type of polymer gel dosimeter, which responds well to absorbed dose even when manufactured in the presence of normal levels of oxygen, was recently described by Fong et al. [Phys. Med. Biol. 46, 3105-3113 (2001)] and referred to by the acronym MAGIC. The aim of this study was to investigate the feasibility of using this new type of gel for intensity-modulated radiation therapy (IMRT) verification. Gel manufacturing was carried out in room atmosphere under normal levels of oxygen. IMRT inverse treatment planning was performed using the Helios software. The gel was irradiated using a linear accelerator equipped with a dynamic multileaf collimator, and intensity modulation was achieved using sliding window technique. The response to absorbed dose was evaluated using magnetic resonance imaging. Measured and calculated dose distributions were compared with regard to in-plane isodoses and dose volume histograms. In addition, the spatial and dosimetric accuracy was evaluated using the gamma formalism. Good agreement between calculated and measured data was obtained. In the isocenter plane, the 70% and 90% isodoses acquired using the different methods are mostly within 2 mm, with up to 3 mm disagreement at isolated points. For the planning target volume (PTV), the calculated mean relative dose was 96.8 +/- 2.5% (1 SD) and the measured relative mean dose was 98.6 +/- 2.2%. Corresponding data for an organ at risk was 34.4 +/- 0.9% and 32.7 +/- 0.7%, respectively. The gamma criterion (3 mm spatial/3% dose deviation) was fulfilled for 94% of the pixels in the target region. Discrepancies were found in hot spots the upper and lower parts of the PTV, where the measured dose was up to 11% higher than calculated. This was attributed to sub optimal scatter kernels used in the treatment planning system dose calculations. Our results indicate great potential for IMRT verification using MAGIC-type polymer gel.
authors.affiliation: Department of Radiation Physics, Land University, Malmö University Hospital, SE-205 02, Malmö, Sweden. helen.gustavsson@rfa.mas.lu.se
authors.forename: Helen
authors.initials: H
authors.lastname: Gustavsson
authors.forename: Anna
authors.initials: A
authors.lastname: Karlsson
authors.forename: Sven A J
authors.initials: SA
authors.lastname: Bäck
authors.forename: Lars E
authors.initials: LE
authors.lastname: Olsson
authors.forename: Pia
authors.initials: P
authors.lastname: Haraldsson
authors.forename: Per
authors.initials: P
authors.lastname: Engström
authors.forename: Håkan
authors.initials: H
authors.lastname: Nyström
mesh_terms: D001205:Ascorbic Acid / Q000528:radiation effects*; D019327:Copper Sulfate / Q000528:radiation effects*; D019544:Equipment Failure Analysis; D005240:Feasibility Studies; D005780:Gelatin / Q000528:radiation effects*; D006801:Humans; D006873:Hydroquinones / Q000528:radiation effects*; D018499:Linear Energy Transfer; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D008689:Methacrylates / Q000528:radiation effects*; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D011108:Polymers / Q000528:radiation effects*; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D006873:Hydroquinones; C476159:MAGIC polymer gel; D008689:Methacrylates; D011108:Polymers; D005780:Gelatin; D019327:Copper Sulfate; D001205:Ascorbic Acid