My husband is 3 1/2 months out of treatment now. How many times per week are recommended for doing the trays?

From what others have discussed on here, flouride trays should be continued to be used daily.

My prosthodontist told me early on that after radiation, I should use my fluoride trays DAILY for the rest of my life, if I want to keep my teeth. If that was not the advice your husband received from his dental professional, my recommendation would be that he ask his medical team for a referral to a dentist who has experience in dealing with the specialized problems that occur after radiation for a consultation. Just like you would not expect your family's general practitioner doctor to be a specialist in oncology or cancer treatment, it could not hurt to have one visit with a dental specialist.
I've been using my fluoride trays daily now for 5 years.
Dental health is a serious concern after radiation TX due to decreased saliva, dry mouth, and radiation damage to the teeth roots and jaw tissues. For example, Extractions are a big No No without Hyperbaric Oxygen treatment.

Daily and make it the last thing he does before he goes to sleep.

His dentist and radiation oncologist both seem to think 3 times a week is ok.

Both my dentist and RO told me to use the flouride everyday. I started using it before I even started radiation. My dentist said I will probably be using the trays for the rest of my life. My RO even told me I could use them twice a day, but most people do not.

Every day is best, but effectiveness is also time-dependent, so if you miss a day do it longer for the next day.

I started using my trays 1 month pre rad and I used them throughout my Tx (well almost every night) and I used them for 5 years post Tx, again almost every night. I was told after 5 years that I didn't need to use them anymore. My rountine... I would floss, brush and then I wore them for 30 mins, took them out and went to bed without drinking anything.

Terrib

I think it's more of risk reduction vs inconvenience issue. IMO, it's not worth the risk of losing my teeth over using a flouride tray since I've seen zero studies suggesting it would be safe to quit using them..
A quick search turned up that the National Cancer Institute at NIH recommends daily use of fluoride trays until such time as full saliva returns. There were some studies on oral cancer patients purporting to show that patients who skipped fluoride trays got cavities and some lost their teeth. But they were not clinical trials, double blind or anything so not proof positive (or else I'd have linked to one of them). If a dental college web site or dental hygienist web site mentioned it,they advocated daily use for life for head and neck cancer patients who had received radiation.
But who knows, maybe three times a week is plenty, it's just that your post is the very first one I've seen since joining OCF that does not say their dentist or RO told them daily use.
Hey, you can let us know in a few years how 3x worked out for your husband
Charm

Terrib, I think you have gotten a comprehensive response. My oral surgeon / dental team who removed my molars prior to rad/chemo advised to fluoride every day...for the rest of my life to keep the remaining teeth. Rather stark advise, but since my saliva is mostly gone, and it is what in the past kept the teeth clean or washed, I get it. Sometimes if I feel ill I skip. The fluoride paste seems to upset my tummy some.

Good Luck and my prayers will be with your hubby and your family.

Ken