My orthopedic doc and urologist/oncologist now accept the below:
Ortho advised only needing Ca in the normal range but taking large supplements of C and D3. Both at least 6,000 IU per day.
Reason is, the D3 and C activate the body's ability to use the Ca for bones. Excess Ca just gets washed out by the kidneys - which can also raise risk of kidney stones.
I'm also on Prolia twice a year for life due to osteoporosis.
At first, onco kept advising Ca but after the above explanation he ok'ed moderate/normal Ca if any and encouraged D3 in particular.
This was all triggered by 5 compression fractured Thoracic vertebrae (those were a "12" pain on the 1 - 10 scale) a year and 1/2 after finishing 2 years of Lupron.
Be sure to consult a orthopedic surgeon of high repute if using any ADT.

PS: my hospital has a "protocol" that DEXA bone scans don't evaluate the spine; only one leg and on arm. So my osteoporosis was a nasty surprise. If I ever get another DEXA it will be at another provider.