@djbaril If I am not mistaken it is NavDx® test . I had the test 3 months after radiation, then 6 month, then 1 year and the next should be 1 year from that test.
Here is information on it.:
Test Name(s): NavDx® test (commercial name), or generally referred to as a test for circulating tumor HPV DNA (ctHPVDNA or TTMV-HPV DNA).
Purpose: To monitor the effectiveness of cancer treatment, confirm remission, and detect recurrence early in patients with HPV-driven cancers, such as oropharyngeal (head and neck) and anal cancers.
Method: It is a blood test, making it minimally invasive compared to tissue biopsies.
Clinical Use: Medicare covers serial NavDx testing for surveillance of recurrence in patients with a history of documented HPV-driven oropharyngeal cancer.
Regular follow-up for HPV-related cancer after treatment typically involves a combination of physical exams, imaging scans (like PET/CT scans), and these specialized blood tests to ensure any potential recurrence is caught as early as possible.
ASTRO: Blood test confirms HPV-related cancer remission

Also, my understanding of the HPV virus is that most people's immune system hold it at bay, and then after a period of time 1-2 years, they no longer have it at all. A few of us just weren't
lucky enough to clear it. Thus cancer! YAY! us. There are many common strains of the virus but the ones that cause cancer are HPV 16 and HPV 18.
It is my understanding that your immune system should be back in about 3 months after radiation (shorter with proton usually because it doesn't effect as much of the bone marrow ) but may take longer if you had chemo. That is the norm. some people may take several months or years depending.
please note that I am not a doctor so I prefaced this with "It is my understanding"
Hope this helps