the radiation field within the target volume since it compensates dose variations delivered to different regions of the tumour due to their changing distance to the seed the lamellae 20 and the compensator structure 36 can be printed by stereolithography methods wherein the lamellae are provided by highly gold doped polyimide while the compensator structure comprises less doting a polymethylmethacrylate pmma block having an overall base size of 30 mm u00d7 30 mm u00d7 10 mm was cut from a pmma block evonik r u00f6hm gmbh using a bandsaw a bore having a diameter of 0 9 mm was drilled through the length of the pmma block parallel to one 30 mm u00d7 30 mm surface using a twist drill bit the remaining wall thickness between the bore and the block surface was 0 4 mm an iodine 125 seed ibt bebig type i25 s16 was fixed in the bore the pmma block was covered with a shielding layer of gold foil goodfellow gmbh of 30 mm u00d7 30 mm and a thickness of 100 u03bcm which formed an opening of 5 mm u00d7 1 mm adapted to the size and the position of the seed a sandwich structure was set up of 25 u03bcm thick layers of gold foil and 100 u03bcm thick layers of polypropylene foil herlitz pbs ag the layers were fit into a slot with a size of 5 mm u00d7 1 mm u00d7 0.