Air density dependence of the response of the PTW SourceCheck 4pi ionization chamber for I-125 brachytherapy seeds

Autors de IIS La Fe

• Luis Guirado Perich

  Autor

• José Pérez Calatayud

  Autor

Autors aliens a IIS La Fe

• Torres del Rio, J.
• Tornero-Lopez, AM
• Lallena, AM

Grups d'Investigació

• Unidad Mixta de Investigación en Radiofísica e Instrumentación nuclear en medicina

  Leader

  Facundo Ballester Pallares

Abstract

Purpose: To analyze the air density dependence of the response of the new SourceCheck 4pi ionization chamber, manufactured by PTW. Methods: The air density dependence of three different SourceCheck 4pi chambers was studied by measuring I-125 sources. Measurements were taken by varying the pressure from 746.6 to 986.6 hPa in a pressure chamber. Three different HDR 1000 Plus ionization chambers were also analyzed under similar conditions. A linear and a potential-like function of the air density were fitted to experimental data and their achievement in describing them was analyzed. Results: SourceCheck 4pi chamber response showed a residual dependence on the air density once the standard pressure and temperature factor was applied. The chamber response was overestimated when the air density was below that under normal atmospheric conditions. A similar dependence was found for the HDR 1000 Plus chambers analyzed. A linear function of the air density permitted a very good description of this residual dependence, better than with a potential function. No significant variability between the different specimens of the same chamber model studied was found. Conclusion: The effect of overestimation observed in the chamber responses once they are corrected for the standard pressure and temperature may represent a non-negligible similar to 4% overestimation in high altitude cities as ours (700 m AMSL). This overestimation behaves linearly with the air density in all cases analyzed. (C) 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Keywords

• Brachytherapy; Low-energy sources; Ionization chamber; Air density dependence; PTW SourceCheck 4pi