Here is some information about chemotherapy and the need for a dexascan....lack of estrogen is the culprit in the onset of osteoporosis.
This is from About.com:
"...Chemo that includes cyclophosphamide, methotrexate, and fluorouracil (CMF) is the combination which is most likely to cause estrogen suppression. Post-chemo medications, such as Tamoxifen and Raloxifene also help to lower estrogen levels, and are important as follow-up for patients who had estrogen-receptor positive (ER+) tumors.
Estrogen levels drop naturally during menopause, and during chemotherapy, many pre-menopausal women experience "chemo-pause" (monthly periods cease or become irregular). Regardless of whether your estrogen levels drop due to natural or chemical menopause, bone health becomes an important thing to discuss with your health care team..."
PS. Arimidex also affects estrogen levels.
Hopes this helps.