chelation and parkinson's

My husband just started seeing a new Dr. last week. He's a D.O. who practices alternative treatments. He is having my husband undergo chelation.... after reading some of the postings on here I'm becoming very concerned because my husband is 65 and has a lot of Amalgam fillings. Please advise..... are there different types of chelation? I dont dare mention this to my husband because he's been under so much emotional stress lately. Last year he was diagnosed with Prostate cancer ... the year before he tore his achillles, I think you get the picture. Someone please tell me this treatment won't hurt him.
Thanks