| Summary: | There have been developments in radiation therapy treatment techiques, which lead to an increase in the complexity of these treatments. The aim is to deliver highly conformal three-dimensional (3D) dose distributions, such as stereotactic radiosurgery (SRS). Polymer gel dosimetry offers three-dimensional (3D) dosimetry techniques for dose verification of dose distributions. Nisopropyl- acrylamide (NIP AM) polymer gel was the latest to develop and can be prepared under a normal atmospheric environment and has lower toxicity compared with the highly toxic polymer gels used earlier. NIPAM polymer gel using X-ray computed tomography (CT) was experimentally investigated in terms of its X-ray CT dose response, sensitivity and dose resolution. The effect of radiation beam type, radiation beam energy and radiation beam dose rate on X-ray CT dose response have also been studied. The temporal stability of NIP AM polymer gel has been examined over several days post-irradiation. The change in the polymer gel dosimeter's physical and electron densities as a function of absorbed dose was also investigated. In ,this study two new prototype phantoms were designed and constructed for imaging and irradiation of polymer gel dosimeters to provide simplicity and practicality for clinical dosimetry. The dosimetric and water equivalence properties of four NIP AM based polymer gel dosimeter formulations have been studied by examining their physical properties, interaction probability, radiation transport parameters and performing Monte Carlo modelling of depth doses. NIP AM polymer gel dosimeter irradiated at different doses using 6 Me V photon beam and 400 MU min-1 dose rate were found to have higher CT dose response (up to 37.8% at 10 Gy dose point) than results reported in the literature for NIP AM gel using similar concentration. The CT dose sensitivity of NIPAM polymer gel was found to be 0.405±0.014 H Gi1 , which is 26.2% higher than the reported sensitivity of 0.32l±0.008 H Gy-l with similar NIPAM gel concentration. The maximum change in physical density as a function of absorbed dose for polymer gel dosimeters was found to be up to ~1.0% for an absorbed dose of 20 Gy. 111
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