A new device for the measurement of the absorbed dose to water for low energy x-ray sources used in brachytherapy

The Physikalisch-Technische Bundesanstalt (PTB) is developing a primary standard to determine the absorbed dose to water within a water phantom for X-ray brachytherapy sources such as I-125 and Pd-103. A candidate for the standard to be newly established is a water-equivalent parallel-plate ionization chamber with continuously adjustable electrode spacing, forming an extrapolation chamber in a phantom of water-equivalent material.