Hello and thank you for your question. My name is ***** ***** I will be happy to assist you today!
You will not be able to bring just any letter from your doctor. Each airline has a specific form that you will need to have completed by your doctor in order to take that on the plane with you.
If you let me know which airline you will be traveling on I can get that form for you.
Let me know if you have further questions and I will be happy to help you with getting the right forms for you so that when you arrive at the airport you will not have any issues and will have the proper paperwork for international travel.