How should radiation oncology departments prepare for significant resource depletion and/or staff shortages with the COVID-19 outbreak?

Resource depletion to the extreme would be analogous to having a non-operational clinic as some experienced during the Hurricane María disaster. I would suggest reading the paper:

Lessons Learned From Hurricane Maria in Puerto Rico: Practical Measures to Mitigate the Impact of a Catastrophic Natural ...

As per FAQ’s posted by ASTRO:

It is important to have clear protocols for COVID-19 and COVID-19-suspected (Patient Under Investigation (PUI) or screen positive patients) who are not undergoing aerosol-generating procedures (e.g., on a ventilator, receiving anesthesia that requires an airway, etc.). ...

As of March 24, 2020, there is a national and global supply shortage of both N95 and standard surgical masks. Standard surgical masks are currently recommended to be worn by therapists who are treating patients with any upper respiratory symptom at several radiation therapy centers. Resupply of mask...