zapper

Could someone please make some recommendations to me about the zapper or another device I should consider? I bought a terminator II for the purpose of clearing Psoriasis on my 12 year old son. He has it quite extensively on his body. We started using the device approximately 4 months ago. He has had very little clearing of the Psoriasis plaques although the center of some of the plaques are clear skin. I would of thought by now that we would have seen more of an improvement. At this rate it could take years. Would anyone here have any advice to share on what I should do next? Thanks to all of you for your help.