Thanks for the background information. Since you will already have a BS, I wouldn't be as opposed to a certificate program. In my opinion, I would be inclined to go the degree route over the certificate in a perfect world. But I doubt you'd benefit much from a second BS, so in the end it might just be a wash anyway.
To be honest, I didnt even know that Jefferson had a medical dosimetry program. The website indicates that the program was started in 2004, so its still a young program. I think it would be wise to speak with the program director prior to applying. Some things you should inquire about would be: CMD board pass rates, number of students per year, program requirements, and student responsibilities. Ask if you will have exposure to IMRT planning, brachytherapy, radiosurgery, etc. Ideally, the key is to be well rounded in all things dosimetry. When you call and talk to the program director see if they'd let you shadow a dosimetrist for a day or two just to get a feel for the job.
There are a few reasons why there are only two accredited degree programs in the US. First, class sizes are so small that its hard for schools to fund programs. Second, even fewer schools/centers have the infrastructure to support a dosimetry program. You need a program director, instructors, and hands on time on treatment planning equipment. This is not to say that non-accredited programs aren't as good as accredited ones, just that they dont meet the standards of the JRCERT.
The MDCB is going trying to eliminate on the job training positions eventually, especially since they are so few and far between these days. Also with the fact that there is only two accredited degree programs, job demand/salary is going to be high for many years to come.
Feel free to drop me a line if you have any other questions