@Joseph *****
In my case, I had already undergone spinal surgery. When I applied for the DTV visa, my doctor confirmed that I would require another surgery in the future. The hospital prepared all the necessary supporting documents, including the doctor's medical letter, as well as a letter addressed to the Royal Thai Embassy in the country where I submitted my DTV visa application.
My follow-up appointments are usually six months, although I also visit the hospital whenever necessary. In addition to my spine condition, I have regular appointments for other minor medical issues as well, so I continue to have ongoing medical follow-ups.
I hope this information is helpful. Wishing you all the best with your application.