CT Scan vs. MRI: Which is safer for those with cancer?

When I learned in January 2017 that my colon cancer had metastasized to my liver, my oncologist, Dr. G, suggested (in addition to 4 rounds of chemo, surgery, and up to 8 more rounds of chemo) a series of scans to monitor the status of my cancer. CT scans of my abdomen and lungs were immediately taken to determine the location of any tumor(s). One tumor was detected on my liver; no other tumors were seen.

Dr. G then referred me for a PET Scan. I'd never had a PET scan and knew nothing about the procedure or possible risks. I was still in a state of shock over my Stage IV-A metastatic diagnosis (and end-of-year death sentence if I did not submit to the chemo / surgery regimen). So, I compliantly agreed to the PET scan. There was a caveat, through. Badger Care (my insurance) would have to approve the scan. A week later I was told that Badger Care refused to pay for the scan because of its cost.

That's when I decided to do some research. What I discovered shocked and upset me!

Fighting Cancer in the Philippines

Map of the Philippines
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This morning I received an e-mail from Mark, a colon cancer patient in the Philippines. His colon cancer is not going away, despite aggressive chemotherapy, surgery, and other procedures.  Just look at what this poor man has endured! Heartbreaking! He's worried, and asked for my advice. 

First, Mark's e-mail:

I was diagnosed with cancer last December 2015, Stage III-B. My CEA at that time was 8.7. I had surgery January 9, 2016. I underwent a very aggressive chemotheraphy twice a month intervals of every two weeks. I was given 5FU, Irenotican, Loucoverin, Oxaliplatin and a booster Avastin. I finished my session July 2016.

My CEA went down to 4.2. The result of my PET scan is very good as well.