Calibration of the LNMRI Secondary Standard Ionization Chamber for 131I capsules used in nuclear medicine

The radionuclide ¹³¹I has been increasingly used in nuclear medicine therapy procedures. Nowadays, the ¹³¹I source administered to the patient is manufactured in two different geometries: solution and capsules. The purpose of this study is the accurate measurement of the activity present in a ¹³¹I capsule without destroys it. The methodology to determine the capsules activity is to obtain the calibration factor of an IG12 secondary standard activity measurement system based on the IG12 well-type ionization chamber set up at Brazilian national metrology laboratory for ionizing radiation (LNMRI) of institute of radiation protection and dosimetry (IRD).The result obtained, 6.4670?±?0.0381?×?10^?18?A?Bq^?1, is quite similar to the calibration factor of the ¹³¹I solution contained in the standard ampoule geometry, 6.4515?±?0.0368?×?10^?18?A?Bq^?1. After obtaining the calibration factor it was used to measure ¹³¹I therapy capsules in order to check the performance of radionuclide calibrators of some Brazilian nuclear medicine centers.