Is there a risk of increased skin toxicity with combined radiation and doxycycline?

No reports that I am aware of. Tetracyclines have an absorption wavelength of ~300-350 nm and can be pushed into an excited energy state by primarily UVA (320-400 nm) waves. Relaxation back to base state leads to chemical reactions that generate photoproducts that serve as antigens in a cutaneous allergic reaction. High-energy X-rays would not activate these pathways. I do encourage patients who are getting significant skin dose to avoid sun exposure and would counsel increased caution for patie...