nuclear stress tests

I have recently been reading varying opinions on the long term risks of nuclear stress tests.  
Ten years ago I was diagnosed with a blocked artery.  A stent or by pass were not recommended.  I have done well since that time.
I am a private pilot, not for hire, and in order to maintain my medical certificate to fly the FAA has required periodic radionucleotide scintigraphy exercise stress tests.  In that time I have had 5 of the nuclear stress tests plus a CT coronary angiogram.  I am scheduled for another nuclear tests this summer.  I am currently 71 years old and will probably only take two more nuclear tests before I retire from flying.
Would this much testing still fall within the safe levels of exposure?

[heartfluttersflyawayplz]

wow and am scared to take one , do you walk the treadmill or shot,   they say very little to harm you so if you have had over the years i guess its not all at one time. hope someone can come on here and give you a the right answer