[en] Interstitial implants with I-125 seeds are generally carried out using a dosimetric system that is based on implanting a specified number of mCi, depending on the average dimension of the gland. It is not clear at the present time whether the dose delivered should vary with the volume of the implant and if so in what manner. In this paper, we describe a protocol in which the mCi and the number of seeds to be implanted are selected on the basis of delivering a prescribed dose in rad. Two specific doses within an implant have been identified and the one is the minimium periphera dose (MPD) and the other one is the maximum central dose. A simple and unique way of accurately assessing the glandular volume at surgery is also described