Evaluation of a new sealed reentrant well chamber for HDR and LDR brachytherapy calibrations.

A new reentrant ionization chamber SNC 1008 has been introduced for low dose rate (LDR) and high dose rate (HDR) brachytherapy source calibrations. There is no air density correction requirement for the chamber since it is hermetically sealed. In this study we evaluate its use for HDR as well as LDR source calibrations. The magnitude of the ionization current collected was found to be independent of the sign of the polarizing voltage within +/- 0.5%. The axial response curve of the well chamber reveals a "plateau region" (+/- 0.5% dose variation) of 4.2 cm, which is larger than the published values for other commercially available chambers. Long-term stability of the chamber was evaluated. Short-term response and source positioning reproducibility were tested using both LDR and HDR sources. Ion collection efficiency was found to be high, making the chamber suitable for HDR 192Ir sources.