Wednesday, September 12, 2012

Battle of the hippocampus

“You have brains in your head. You have feet in your shoes. You can steer yourself any direction you choose. You're on your own. And you know what you know. And YOU are the one who'll decide where to go...”  --Dr. Seuss, “Oh, the Places You’ll Go!”

The hippocampus is the elongated
structure in the center of the brain.
If you don’t know what the hippocampus is or where it’s located, permit me to be your guide. If you once knew this but forgot, then I hope to show you the irony of your situation. I didn’t know or care about this part of my brain until recently, but I've become quite attached to it and am now insisting that my radiation oncologist go easy on it during my impending course of whole-brain radiotherapy.

Let me explain why this small structure looms so large to me.
The hippocampus is found in the depths of the temporal lobe—roughly in the center of the brain. It’s part of the limbic system and is integral to how we consolidate information from short-term to long-term memory and to spatial navigation (think of it as your internal GPS). We each have two hippocampi, one on either side of the brain. When they’re damaged, as they can be by therapeutic radiation, loss of memories and disorientation are among the first symptoms. Because most of us are left brain dominant, the left hippocampus plays an especially key role in cognitive function.

This should explain why I’ve taken a sudden interest in this scorpion-shaped part of my brain. It’s bad enough to be told you need radiation therapy, but worse to have one’s brain in the gun sights of a linear accelerator. Worst of all is to know that had I not spoken up, my radiation oncologist was prepared to irradiate my whole brain—hippocampi be damned.
I’m not sure exactly how this will play out in coming weeks, but Dr. Curti, who is directing my care, agrees that the radiation plan that is being designed for me this week should spare the hippocampus. “Although not yet 100% proven, it is plausible that cognitive function would be better preserved with this plan,” he told me by email. Let me emphasize: Radiation will likely knock my thinking down a peg or two regardless of how the field is contoured, but avoiding the hippocampus should minimize its impact. I'm convinced this is the best approach for me.

This strategy can be accomplished by using something called intensity-modulated radiotherapy (IMRT). This advanced mode of high-precision RT uses computer-controlled x-ray generators to modulate the intensity of the radiation beam in multiple small volumes. Using data from a CT scan I got yesterday, a radiation map can be prepared that spatially carves out my hippocampi. While the rest of my brain receives a uniform dose of 40 gray over 20 fractions (sessions), I’m counting on my hippocampi being exposed to very few photons.
Radiation therapy in general stops cancer cells from dividing and growing, thus slowing or stopping tumor growth. In some cases, it’s capable of killing all cancer cells in a region of interest, which is the ambitious goal in my situation. There are undoubtedly millions of cancer cells scattered through my brain right now, some unknown portion of them distant from where my tumor was resected. Because of probable side-effects, which include some degree of cognitive decline, whole-brain RT is not entered into lightly. I have become an ardent student of the subject and know only too well the downside risks. I’m committed to seeing them mitigated to the best of my ability.

It’s worth noting that when I had RT after lymph nodes were dissected from the left side of my groin in 2008, there was no recurrence of cancer in that region. I also experienced no sexual dysfunction or urinary incontinence that I was warned could result from scattered radiation. There is extensive fibrosis in my left thigh that was caused by the radiation, but it hasn’t kept me from running. Lymphedema, which plagues many patients, has not been a problem for me.
I’m using the same radiation oncology group this time around that I did then because I was so pleased with the outcome. We also went 20 rounds (fractions) of radiation over four weeks back then, so I’m attracted to that schedule as a secondary means of minimizing long-term effects in my brain.

The brain is not the groin, however—in case you haven't noticed. The radiation oncologist with whom I met yesterday understands, as I do, that a second round of cancer in the brain could be even more disastrous than my first. We both want to avoid that. But I’m willing to draw the line on how far I’ll go in that battle. I’m prepared to trade off a slightly higher risk of recurrence for what appears to be a much lower risk of short-term memory loss. We can do this by fudging on making whole-brain radiation slightly less than the whole brain (by about 3% of its volume).
When I mentioned to Dr. S yesterday my expectation that we spare the hippocampus, she pushed back. She believes that because my brain tumor had grown into the dura mater, it wasn’t wise to exclude any portion of the brain from the radiation field her team is charged with designing. She added that the dura “wraps around” the hippocampus. I then mentioned the published research that shows how the risk of neurocognitive deficit can be reduced by using IMRT and asked that she look into this and speak with Dr. Curti about it. I expect to find out this week where that takes us exactly.

Dr. S was on the faculty at the University of Washington Medical Center for 18 years, including a stint as director of the radiation oncology program. I respect her clinical judgment overall, but I believe this is a good example of how being an informed patient and seeking to have a dialog about your treatment with a physician can sometimes result in better quality care. As Dr. Seuss might have said, you're on your own in wending your way through the cancer care labyrinth. You are your best advocate.
The fact remains that the cancer in my brain could recur regardless of how it’s treated. The statistics are daunting (see “My brain trust”). It’s also true that even if we use IMRT and my hippocampus is not exposed to radiation, I could still experience cognitive decline. While it’s understood that other areas of the brain are fairly resilient to low radiation doses and experience little or no injury, there are no guarantees—as almost every doctor throughout this process has reminded me. Lastly, and not insignificantly, whether my insurance provider will pay the higher cost of IMRT remains unresolved.

I’m taking a break from all these head-splitting complexities the next couple of days by driving with my son, Nick, to Ashland for a couple of days. We’ll visit friends, drink hand-crafted beer and enjoy outdoor theater at the Shakespeare Festival. I’m counting on my hippocampus to file away the good memories we accumulate on this trip so I can savor them for years to come.

2 comments:

Thandi said...

Enjoy your time away...

Ada said...

This post is a joy to read - thanks! I've heard Ashland is a wonderful place. I'm pretty sure you'll enjoy that trip.