title: Does nitrogen gas bubbled through a low density polymer gel dosimeter solution affect the polymerization process?
abstract: BACKGROUND
  On account of the lower electron density in the lung tissue, the dose distribution in the lung cannot be verified with the existing polymer gel dosimeters. Thus, the aims of this study are to make a low density polymer gel dosimeter and investigate the effect of nitrogen gas bubbles on the R2 responses and its homogeneity.
  
  
  METHODS
  Two different types of low density polymer gel dosimeters were prepared according to a composition proposed by De Deene, with some modifications. In the first type, no nitrogen gas was perfused through the gel solution and water. In the second type, to expel the dissolved oxygen, nitrogen gas was perfused through the water and gel solution. The post-irradiation times in the gels were 24 and 5 hours, respectively, with and without perfusion of nitrogen gas through the water and gel solution.
  
  
  RESULTS
  In the first type of gel, there was a linear correlation between the doses and R2 responses from 0 to 12 Gy. The fabricated gel had a higher dynamic range than the other low density polymer gel dosimeter; but its background R2 response was higher. In the second type, no difference in R2 response was seen in the dose ranges from 0 to 18 Gy. Both gels had a mass density between 0.35 and 0.45 g.cm(-3) and CT values of about -650 to -750 Hounsfield units.
  
  
  CONCLUSIONS
  It appeared that reactions between gelatin-free radicals and monomers, due to an increase in the gel temperature during rotation in the household mixer, led to a higher R2-background response. In the second type of gel, it seemed that the collapse of the nitrogen bubbles was the main factor that affected the R2-responses.
authors.affiliation: Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Daryoush
authors.initials: D
authors.lastname: Shahbazi-Gahrouei
authors.affiliation: Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Mehrdad
authors.initials: M
authors.lastname: Gholami
authors.affiliation: Department of Biophysics and Biochemistry, School of Medicine, Mazandaran University of Medical Sciences, Sari, Iran.
authors.forename: Tayyeb Allahverdi
authors.initials: TA
authors.lastname: Pourfallah
authors.affiliation: Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Keshtkar
keywords: Low density polymer gel dosimetry; magnetic resonance imaging; nitrogen gas; radiation therapy