The effect of gel homogeneity on dose response in a low-density polymer gel dosimeter for radiation therapy

Background: The human body consists of a variety of tissues and cavities with different physical and radiological properties. The most important among these are tissues and cavities including lungs, oral cavities, teeth, nasal passages, sinuses, and bones. Thus, the dose distribution in these tissues cannot be verified with soft tissue equivalent polymer gel dosimeters. This study is conducted to evaluate the effect of homogeneity on dose response of an anoxic low-density polymer gel dosimeter for radiation therapy. Materials and Methods: The low-density polymer gel dosimeter is composed of 12% gelatin, 5% methacrylic acid, 0.15% sodium dodecyl sulfate, 10 mm tetrakis (hydroxymethyl) phosphonium chloride, and 83% ultrapure deionized water. The time between irradiation and scanning for all gels experiments was 18 h. The gel dosimeters were imaged using a 1.5 T clinical magnetic resonance imaging scanner in a transmitter/receiver head coil. Results: The low-density gels had a mass density between 0.35 g/cm(3) and 0.45 g/cm(3) and the computed tomography (CT) values varied from approximately -650 to -750 Hounsfield units. It is clear that the CT numbers of the fabricated gel are close to those of the normal human lung tissue, which ranges from -770 to -875 Hounsfield units. Conclusion: Findings of the present study showed that if the density and homogeneity of the low-density polymer gel dosimeters are equal to those of the normal lung tissue, it may be used to measure the three dimensional dose distributions in lung tissue during radiation therapy.