A Comprehensive Evaluation of NIPAM Polymer Gel Dosimeters on Three Orthogonal Planes and Temporal Stability Analysis

• Published in: PloS one Vol. 11; no. 5; p. e0155797
• Main Authors: Cheng, Kai-Yuan, Hsieh, Ling-Ling, Shih, Cheng-Ting
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 18.05.2016; Public Library of Science (PLoS)
• Subjects: Acrylic Resins - chemistry; Biology and Life Sciences; Calibration; Conversion; Dimensional stability; Dosimeters; Dosimetry; Evaluation; Feasibility studies; Gels; Image acquisition; Irradiated; Isopropylacrylamide; Magnetic resonance; Magnetic resonance imaging; Mathematical analysis; Medical imaging; Medicine and Health Sciences; NMR; Nuclear magnetic resonance; Orthogonality; Patient outcomes; Phantoms, Imaging; Physical Sciences; Physiological aspects; Planes; Polymer gels; Polymerization; Polymers; Radiation; Radiation dosage; Radiation Dosimeters - standards; Radiation therapy; Radiotherapy; Radiotherapy, Intensity-Modulated - instrumentation; Reaction time; Reproducibility of Results; Research and Analysis Methods; Science; Sensitivity and Specificity; Stability analysis; Ultrasonic imaging; Taiwan; China
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0155797

Polymer gel dosimeters have been proven useful for dose evaluation in radiotherapy treatments. Previous studies have demonstrated that using a polymer gel dosimeter requires a 24 h reaction time to stabilize and further evaluate the measured dose distribution in two-dimensional dosimetry. In this study, the short-term stability within 24 h and feasibility of N-isopropylacrylamide (NIPAM) polymer gel dosimeters for use in three-dimensional dosimetry were evaluated using magnetic resonance imaging (MRI). NIPAM gels were used to measure the dose volume in a clinical case of intensity-modulated radiation therapy (IMRT). For dose readouts, MR images of irradiated NIPAM gel phantoms were acquired at 2, 5, 12, and 24 h after dose delivery. The mean standard errors of dose conversion from using dose calibration curves (DRC) were calculated. The measured dose volumes at the four time points were compared with those calculated using a treatment planning system (TPS). The mean standard errors of the dose conversion from using the DRCs were lower than 1 Gy. Mean pass rates of 2, 5, 12, and 24 h axial dose maps calculated using gamma evaluation with 3% dose difference and 3 mm distance-to-agreement criteria were 83.5% ± 0.9%, 85.9% ± 0.6%, 98.7% ± 0.3%, and 98.5% ± 0.9%, respectively. Compared with the dose volume histogram of the TPS, the absolute mean relative volume differences of the 2, 5, 12, and 24 h measured dose volumes were lower than 1% for the irradiated region with an absorbed dose higher than 2.8 Gy. It was concluded that a 12 h reaction time was sufficient to acquire accurate dose volume using the NIPAM gels with MR readouts.