Question of Engaging in Parkruns While Under Cancer Treatment

As far as my ongoing condition as a brain cancer patient is concerned, I recognize that I do not have extensive specialized technical schooling and training as a medical student or resident physician.  But I am fluent in my own language and can reason things out, given a reasonably simple explanation of my condition and the available options at my disposal to improve it. It looks as if I will soon be driven often to receive oncological treatment, either in the form of chemotherapy or radiation.  That's bound to cause some adverse side effect reactions from me, so I could use help with loved ones encouraging my activity and physical fitness in the face of what may look to be a grueling, extended period of time. My hope is to return to a fitness level in which I can effectively participate in the weekly Parkrun events, two of which are held in the Gainesville area. I just don't need anyone trying to talk me out of a swath of my remaining life here on Earth with overly technical scare-language.  Neither am I interested in following hyper-competitive elitists who just don't understand the larger issues in these events.  If you're a fast boy between 11 and 14, you have your whole life ahead of you...go ahead, run fast and be happy. I just turned 69 and am generally considered "beyond employment".  Let the competitors in these Parkruns try to beat each other (and me) out: just dispense with your sarcasm and move on if you haven't anything positive to contribute...