For someone w/ thyroid cancer, the tsh is suppressed to <0.01. does one need to follow a dexa?

Yes: Hyperthyroidism, especially for long periods of time, can cause osteoporosis. You should at least have an initial DXA for baseline and then followed 1-2 years after that if your doctor is going to keep your tsh< 0.01 all that time.

Not usually: The TSH suppression to so make sure that thyroid gland tissue which may remain is not stimulated to grow. Growth hormone is much more involved in bone density, even though thyroid hormone can affect it. Dexa scans can be performed as they normally would for a patient of appropriate age and other risk factors for osteoporosis.

Yes: Long term suppression of TSH (hyperthyroidism) can induce osteoprosis. A baseline DEXA scan is appropriate.