2 questions: Interpretation of CA19-9. SBRT methods.

Hi. I was diagnosed with inoperable pancreatic cancer stage 4. Locally advanced. I am in my 16th session if folfirinox. After session 3-4, irinotecan was removed due to slurred speech and leg shakes. But it was reintroduced for sessions 14 and beyond at a slower rate and so far so good. But the oxilaplatin was removed after session 13 due to neuropathy. Right before session 13 my CA19-9 started to slowly increase. Originally over 2500, then dropped to 65 after session 12. Now it’s creeping back up. Today it was 222. One doctor says it’s cuz cancer is active. Another said this fluctuation is not unusual. I know some docs are very black and white and some sugar coat things. These blood tests are the only thing we have between the two months scans to “see what’s going on” and the increase is scaring me. Scans right before session 13 showed stable disease and no evidence in liver at all. MRI last week showed the same. Waiting for pet scan which was ordered for re staging and possibly adding radiation (SBRT) treatments.

Has anyone had this happen with the CA-19-9??

Also SBRT was suggested by local docs using the standard 5 treatments but I read an article from memorial Sloan Kettering where it’s done in several sessions during an MRI in order to do less damage to near by organs. Has anyone done this??

Below is article in case it helps someone else:
https://urldefense.com/v3/__https:/www.mskcc.org/news/high-dose-radiation-offers-hope-people-inoperable-pancreatic__;!!KGKeukY!zaJIRXFrpB6huZCIYcARFzB0I5fttlwHf9uZG6KLcGnUxGc0FMjEA4pxXzKyW9dJeVzUc8sSoyyreT46EPq-JTLFeebqGQ$
Thanks for your input for both questions.