Well, after a Sports Medicine Doctor's assessment, it looks like the only thing I can do to help with the calf cramping I am getting at about 15 miles is to continue what I am doing. Running, stretching, ART (Active Release Therapy), yoga, and maybe add some massage.
After my 19.25 mile run ended in a long walk after cramps/pain set in at 15.5 miles I scheduled a visit to a Sports Medicine Doctor at PSI Sports Medicine, at the Palladium (home of the Senators). I had the appointment yesterday and it went well enough. My symptoms do not show signs of Lower Extermity, Compartment Syndrome, a blood clot, or a stress fracture.
The Doctor did warn me that if the pain moved from the entire calf region to the front of my leg and became acute then I need to stop as this could be a sign of a stress fracture. A broken bone while running is not cool he informed me (ya, I could guess that).
In general he said it is probably just a cramp brought on by muscle exhaustion or any number of other items that could cause a cramp. The pain and radiating into my knee does not sound like a problem since it goes away once I rest the leg for a while or if I walk it off.
So, plan for the next two weeks. More ART, more stretching, more yoga, and maybe a massage or two.
After the marathon, it is back to the drawing board as I work on a new training schedule and strengthening regime to improve the endurance and length of my calfs (length equating to less tight calf muscles). It's stay on track and continue training since that is part of my overall healthy living plan and I don't intend this first marathon to be the last.