Your calcium score indicates some advancement of coronary artery disease. The score represents plaque buildup within the coronary 3 layers. The 40 to 50% stenosis can be remodeling of the veessel that is is 40 to 50% narrower than normal (negative remodeling of the vessel) or it can be the plaque buildup in the lumen (channel) of the vessel.
Regardless almost always there are no symptoms with 40-50% narrowing of the vessel channel, and no interventional treatment is recommended. Your doctor probaly want you to keep your cholesterol within limits with proper diet, exercise, etc. That is about all that an individual can do as there is no reversing of plaque buildup. My score in all 4 arteries is over 250 individually and a total score over 1000 as I remember.
Hope this provides a perspective, and thanks for sharing. Take care.
Ken