A template, to be provided at some distance from the skin, provided with multiple guide holes for needles or catheters of which one or more can anchor in the prostate. The template is provided with a locking mechanism so that, after placement, the anchored needles keep all needles in their original places. The above-described method of fixedly positioning a treatment template prevents the needles from moving due to swelling of the tissue in the prostate, which causes the irradiation source, which is later provided in the needles, to improperly irradiate the area.