Constancy checks of HDR well-type ionization chambers in the linac era: Potential use of a ⁹⁰Sr source

A methodology using a⁹⁰Sr source, originally designed for constancy checks of parallel-plate ionization chambers, was proposed for constancy checks of HDR brachytherapy well-type ionization chamber (WTIC). The ⁹⁰Sr source was positioned on the top of the WTIC, a reference reading value was established, and the constancy variation was calculated by the difference between each subsequent measurement and the reference value. This methodology was validated by calibrated ¹⁹²Ir sources measurements and an acceptable tolerance limit for constancy variation of 1.5% was suggested.