As a patient, I believe very much in medical baselines when they serve a purpose of reassurance, yours or your specialists, in an otherwise slightly medical quandary. This might not be a view that is favoured by many on the medical side of the fence and that might be due in part because hypochondria walks hand in hand with medical paranoia. Nonetheless, when your livelihood is dependant upon that six monthly medical, it behoves one both to take care of the body and to be aware of any subtle internal changes of parameter that might presage something rotten this way coming.
The Mayo Clinic informs those interested that the risk of cancer caused by radiation from a CT coronary angiogram is small. There is of course no risk from radiation in a coronary angiogram but that might suit your requirements. The risk of death or life changing damage from a heart seizure or stroke might be greater?
There is one person on this forum who I am sure would be well able to answer your query. For my part, in the absence of specific medical advice, I'd take the non invasive procedure and have a definite answer to what seems to be a confused situation.