MAGIC-type polymer gel for three-dimensional dosimetry: Intensity-modulated radiation therapy verification

• Published in: Medical physics (Lancaster) 2003-06, Vol.30 (6), p.1264-1271
• Main Authors: Gustavsson, Helen, Karlsson, Anna, Bäck, Sven Å. J., Olsson, Lars E., Haraldsson, Pia, Engström, Per, Nyström, Håkan
• Format: Article
• Language: English
• Subjects: 3D verification; Accelerators; Ascorbic Acid; Ascorbic Acid - radiation effects; Biofysiks; Biologi; Biological Sciences; biomedical MRI; Biophysics; Collimation; collimators; Comparative Study; Computer software; Copper Sulfate; Copper Sulfate - radiation effects; dosimetry; Dosimetry/exposure assessment; Equipment Failure Analysis; Evaluation Studies; Feasibility Studies; Gelatin; Gelatin - radiation effects; Gels; Gels and sols; Humans; Hydroquinones; Hydroquinones - radiation effects; IMRT; Intensity modulated radiation therapy; intensity modulation; linear accelerators; Linear Energy Transfer; Magnetic Resonance Imaging; Magnetic Resonance Imaging - instrumentation; Magnetic Resonance Imaging - methods; Manufacturing; Medical treatment planning; Methacrylates; Methacrylates - radiation effects; Models, Theoretical; MRI; Multileaf collimators; Natural Sciences; Naturvetenskap; Phantoms, Imaging; polymer gel dosimetry; polymer gels; Polymers; Polymers - radiation effects; radiation protection; radiation therapy; Radiation therapy equipment; Radiometry; Radiometry - instrumentation; Radiometry - methods; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Radiotherapy Planning, Computer-Assisted - methods; Radiotherapy, Conformal; Radiotherapy, Conformal - methods; Reproducibility of Results; Research Support, Non-U.S. Gov't; Sensitivity and Specificity; Treatment strategy; Validation Studies; Wedges and compensators
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.1576392

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.