All I submitted for my DTV was a letter from my doctor I see in Bangkok. She said I was a patient of hers and the hospital, it had my passport number and my hospital ID number. It was on an official hospital letterhead and signed by her. I wasn't asked for any other documents and was approved in 5 days.
All I submitted was a letter from my doctor in Bkk that stated I am a patient of hers and that hospital. It was on official hospital letterhead and signed by the doctor. Was approved no problem with no additional documents requested.