What is the process for applying for a DTV visa for health care in Thailand?

You first need to speak to the hospital where you will receive the treatment. They need to draw up a treatment plan for you of well over 6 months duration but they will likely want to examine you first. The treatment plan must be signed off by a recognised medical professional at a legitimate medical facility and be on official letterhead. Once you have this you can apply showing the 500k baht or equivalent in your bank account, but they may also want to see how you can support yourself for the duration of the visa.