Does nitrogen gas bubbled through a low density polymer gel dosimeter solution affect the polymerization process?

Authors

1 Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran

2 Department of Biophysics and Biochemistry, School of Medicine, Mazandaran University of Medical Sciences, Sari, Iran

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 R 2 responses and its homogeneity.
Materials and 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 R 2 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 R 2 response was higher. In the second type, no difference in R 2 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.
Conclusion: 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 R 2 -background response. In the second type of gel, it seemed that the collapse of the nitrogen bubbles was the main factor that affected the R 2 -responses.

Keywords

1.
Baldock C, De Deene Y, Doran S, Ibbott G, Jirasek A, Lepage M, et al. Polymer gel dosimetry. Phys Med Biol 2010;55:R1-63.  Back to cited text no. 1
    
2.
Yoshioka M, Hayashi S, Usui S, Haneda K, Numasaki H, Teshima T, et al. A new polymer gel dosimeter composed of methacrylic acid, agarose gel and THPC with gelatin. 5 th International Conference on Radiotherapy Gel Dosimetry (DOSGEL 2008). J Phys Conf Ser 2009;164:66-9.  Back to cited text no. 2
    
3.
McAuley KB. Fundamentals of polymer gel dosimeters. 4 th International Conference on Radiotherapy Gel Dosimetry. J Phys Conf Ser 2006;56:35-44.  Back to cited text no. 3
    
4.
Oldham M, Siewerdsen JH, Shetty A, Jaffray DA. High resolution gel-dosimetry by optical-CT and MR scanning. Med Phys 2001;28:1436-45.  Back to cited text no. 4
    
5.
Akhlaghpoor S, Zahmatkesh MH, Pourbeigi H. 3D MRI gel dosimetry based on image intensity (A new approach). Iran J Radiat Res 2003;1:45-50.  Back to cited text no. 5
    
6.
Karlsson A, Smulders B, Gustavsson H, Bäck SÅ. IMRT prostate dosimetry using a normoxic polymer gel and MRI. Third International Conference on Radiotherapy Gel Dosimetry. J Phys Conf Ser 2004;3:284-7.  Back to cited text no. 6
    
7.
Nazir A, Afzal M, Buzdar SA. Effects of variation of MRI parameters on signal homogeneity: A qualitative analysis for ferrous benzoic xylenon orange gel. J Pak Med Assoc 2010; 60:470-3.  Back to cited text no. 7
    
8.
Crescenti RA, Bamber JC, Oberai AA, Barbone PE, Richter JP, Rivas C, et al. Quantitative ultrasonic elastography for gel dosimetry. Ultrasound Med Biol 2010;36:268-75.  Back to cited text no. 8
    
9.
Pourfallah TA, Allahverdi M, Alam NR, Ay MR, Zahmatkesh MH. Verifying the accuracy of dose distribution in Gamma Knife unit in presence of inhomogeneities using PAGAT polymer gel dosimeter and MC simulation. Iran J Radiat Res 2009;7:49-56.  Back to cited text no. 9
    
10.
AAPM Report of Task Group No. 85 of the radiation therapy committee, 2004. Tissue Inhomogeneity Corrections for Megavoltage Photon Beams.  Back to cited text no. 10
    
11.
Gum F, Scherer J, Bogner L, Solleder M, Rhein B, Bock M. Preliminary study on the use of an inhomogeneous anthropomorphic Fricke gel phantom and 3D magnetic resonance dosimetry for verification of IMRT treatment plans. Phys Med Biol 2002;47:N67-77.  Back to cited text no. 11
    
12.
Olberg S, Skretting A, Bruland O, Olson DR. Dose distribution measurements by MRI of a phantom containing lung tissue equivalent compartments made of ferrous sulfate gel. Phys Med Biol 2000;45:2761-70.  Back to cited text no. 12
    
13.
Balcom BJ, Lees TJ, Sharp AR, Kulkarni NS, Wagner GS. Diffusion in Fe (II/III) radiation dosimetry gels measured by magnetic resonance imaging. Phys Med Biol 1995;40:1665-76.  Back to cited text no. 13
    
14.
Baldock C. Historical overview of the development of gel dosimetry: Another personal perspective. J Phys Conf Ser 2009;164:012002.  Back to cited text no. 14
    
15.
Sedaghat M, Bujold R, Lepage M. Impact of oxygen on the accuracy and precision of normoxic polymer gel dosimeters. IC3DDose: The 6 th International Conference on 3D Radiation Dosimetry. J Phys Conf Ser 2010;250:012017.  Back to cited text no. 15
    
16.
De Deene Y. How to scan polymer gels with MRI? IC3DDose-The 6 th International Conference on 3D Radiation Dosimetry J Phys Conf Ser 2010;50:68-78.  Back to cited text no. 16
    
17.
De Deene Y, Vergote K, Claeys C, De Wagter C. Three dimensional radiation dosimetry in lung-equivalent regions by use of a radiation sensitive gel foam: Proof of principle. Med Phys 2006;33:2586-97.  Back to cited text no. 17
    
18.
Haraldsson P, Karlsson A, Wieslander E, Gustavsson H, Bäck SA. Dose response evaluation of a low-density normoxic polymer gel dosimeter using MRI. Phys Med Biol 2006;51:919-28.  Back to cited text no. 18
    
19.
De Deene Y, Vandecasteele J, Vercauteren T. Low-density polymer gel dosimeters for 3D radiation dosimetry in the thoracic region: A preliminary study. IC3DDose 2012; 7 th International Conference on 3D Radiation Dosimetry. J Phys Conf Ser 2012;444:204.  Back to cited text no. 19
    
20.
Salomons GJ, Park YS, McAuley KB, Schreiner LJ. Temperature increases associated with polymerization of irradiated PAG dosimeters. Phys Med Biol 2002;47:1435-48.  Back to cited text no. 20
    
21.
Lepage M, Jordan K. 3D dosimetry fundamentals: Gels and plastics. IC3DDose- The 6 th International Conference on 3D Radiation Dosimetry 2010;250:253-61.  Back to cited text no. 21