Strontium Citrate vs Risedronate

Is strontium citrate an acceptable substitute for calcium supplements? Does it have undesirable risks/side effects. I am a female over 70 with Dx invasive ductal breast cancer, osteoporosis, taking Letrozole?
My Endocrinologist is recommending Risedronate, I am currently taking Calcium & Vitamin D supplements. Although I have a history of kidney stones I have not had any for 5 or so years.