Jim Humble's book can explain it better than me, but Chlorine is a loose ion molecule, very reactive and potentially fatal if ingested in high amounts. Chlorine dioxide is a composite molecule ClO2, chemically VERY different in potential variance and degradation pathways, and PROVEN (not by me, but others) to be very safe for ingestion and far more powerful oxidizer that chlorine.
ClO2 has been studied a lot in health trials for human safety.
Honestly, if a Dr. tells you ClO2 is just chlorine he doesn't know about basic chemistry, nor I think I will schedule with such a guy.
Look for someone who works in the chemistry industry, they will be challenged to learn and will be able to better explain you about Miracle-Mineral-Supplement .
I have such a friend and I also took some chemistry classes on college, as part of my career path.
But again, don't take my word for it, go ask. If that Dr. still says it's just chlorine, at least ask him to explain you why, say you're interested to know the details. You'll be amazed at how quickly he'll become overwhelmed in his own mess (I recently did that here, the guy hates me now :) )