Evaluation of dosimetry a performance parameter for a homemade farmer-type ionization chamber according to IEC60731

Document Type : Conference Proceedings


1 MSc in Medical Radiation Engineering, Department of Radiology, Faculty of Engineering, Islamic Azad University, Research Branch, Tehran, Iran. Tel: 09124688658, Fax: 02634257058, Email: z.saberi97@yahoo.com

2 Radiation Application Research School, Nuclear Science and Technology Research Institute (NSTRI), Atomic Energy Organization of Iran (AEOI), Secondary Standard Dosimetry Laboratory (SSDL), Pars Isotope Co., Karaj, Iran,


Introduction: Due to its simplicity, fast response and high reliability, ion chamber detectors
are one of the most suitable dosimetry instruments for X and gamma rays. The dosimeter
 of photon beams, which used in radiotherapy centers, requires high accuracy and should pass requirements of IEC 60731 standards. About 80 percent of the IEC 60731 standard tests such as stability, leakage current, the dose-response linearity, repeatability and resolution were assessed and the results were compared with the values reported by the standard. All tests were carried out on the PTW-30001 Farmer-type chamber and the response was compared with the manufactured chamber.
Materials and Methods: In this study, according to the IEC 60731, IAEA guidelines and standards, using Cobalt-60 gamma radiation, the dosimetric and functional parameters of an ionization cavity detector of a cylindrical Farmer-type with sensitive volume of 0.6 cc, (homemade 0.6 cc Cylindrical Ionization Chamber), compared and calibrated against the calibrated reference Farmer chamber response (PTW-30001).
Results: By applying minimum dose, leakage current was ±0.35 % and It was reduced by less than 1 % after radiation exposure. The percentage change in stability was ±0.3 %. Angular dependency in the chamber response was +0.2 %. Temperature effect on chamber reading was +0.2 % and the repeatability error was ±0.2 %.
Conclusion: Unlike a simple look, Farmer-type chambers have their own technical complexity and cannot easily be used as a dosimeter by doing a few simple tests. Therefore, the IEC 60731 has been developed to address these complexities and introduce them as requirements for the application of an ionization chamber. The present work was a part of the project of manufacturing and commercializing a Farmer-type ionization chamber at the Nuclear Science and Technology Research Institute (NSTRI) in order to face the ahead challenges and try to resolve them. Most of the challenges that come from the technical knowledge and experience can be solved. All of the tests performed well with the standard requirements, but at the same time, compared to the reference ion chamber performance. There was negligible difference between the PTW reference chamber and the criteria required in the standard which demonstrates well-designed PTW chamber.