Hi Maura, glad to hear Don is doing well.
Has he by any chance started any new medications recently? Ace Inhibitors such as Cilazopril are notorious for producing a dry cough. These are used for blood pressure control.
Maybe he should see your primary care physician in the meantime. A simple chest X-ray may help elucidate matters and set your mind at rest.
Tammy

Caregiver/advocate to Husband Kris age 59@ diagnosis
DX Dec '10 SCC BOT T4aN2bM0 HPV+ve.Cisplatin x3 35 IMRT.
PET 6/11 clear.
R) level 2-4 neck dissection 8/1/11 to remove residual node - necrotic with NED
Feb '12 Ca back.. 3/8/12 total glossectomy/laryngectomy/bilat neck dissection/partial pharyngectomy etc. clear margins. All nodes negative for disease. PEG in.
March 2017 - 5 years disease free. Woohoo!