Some Final Concerns

Last Saturday, November 14, about 90 days after my surgery I had my first post-op MRI. Here is the shot most comparable to the initial MRI which I earlier posted on the upper right hand portion of this blog:
If you look closely enough you can still see the tumor but it is now much lighter in color.

When I first read the report accompanying the MRI, my heart sank. The report stated that the remnant was a 3.5 cm tumor measuring 3.5 x 2.5 x 3.1. While this was significantly smaller then the pre-op size (a 4.1 cm tumor measuring 3.8 x 4.1 x 3.7), a 3.5cm tumor would still be larger than the theoretical maximum of 3 cm which would make it "gamma knife-able".

A visit to Dr. Mercado provided some comfort. He explained that since the tumor was now irregularly shaped (no longer round or spherical), the normal convention of using the longest dimension to describe a tumor was no longer applicable. In short, this is not really a 3.5cm tumor. When we have a computer compute the actual volume of this irregular shape it would be smaller than 3.5 cm., he said.

Ok, that made sense. In their original and untouched form, tumors tend to be spherical, which would mean they measure roughly the same in all directions: (note my initial measurements of 3.8 x 4.1 x 3.7) No matter which direction we roll this sphere, we would get roughly the same measurement so it is reasonable to use the convention of using one side's measurement as the tumor size.

Once we cut away a portion of the tumor via surgery -
then things change because the tumor now becomes irregularly shaped or non-symmetrical. While one side might still be 4cm in length, we cannot reasonably refer to this as a 4cm tumor because it is undeniably smaller than the original one.

So like I said, the consultation with Dr. Mercado brought some measure of comfort. So I made some agreeable noises, put on a reasonably happy face and acted like everything was great. As Amarillo "Slim" Preston once said: "There is no need for me to be a hardship on my family the times I do lose."

Still, I had three worries -

1) While I was convinced that the volume of the remaining tumor was less than 3.5cm, when I looked at the measurements 3.5 x 2.5 x 3.1 I also realized that the actual volume would definitely be greater than 2.5 cm, which would make it very close to the theoretical 3cm maximum. How do I know this? Well, how do we find the volume of an irregularly shaped tumor? One way would be to make it a spherical one so that we could use the original measurement conventions. In making it spherical we make it symmetrical. To make it symmetrical we make the longer sides shorter and the shorter sides longer until all three sides are equal. As the shortest side, the 2.5cm side would inevitably become longer, and that's how I knew that the actual volume could not be smaller than 2.5cm. It would be somewhere between 2.5cm and 3.5cm, maybe 3cm, dangerously close to the theoretical maximum. Using only a calculator we can even figure out the length of an "equalized" side by adding up the three dimensions and dividing by three. The result = 3.0333cm!! Right on the maximum! Now I was really starting to worry.

I went so far as to test my theory using clay. I cut out a piece of clay which would measure 3.5cm on 1 side

2.5cm on another

and 3.1cm on the third and final side

Then I rolled it into a sphere and measured that sphere

I don't know if that's 3.033 but it's close enough for me. So this was my obvious worry: if we're on the maximum "gamma knife-able" size would this mean that there would be a significant chance of failure?

2) Even if we were okay on volume, is it okay for one side to be more than 3cm? This is a real issue. For instance, airlines not only put a limit on the weight of our baggage but also on the dimensions, because if one dimension is too long, it might not fit in the baggage hold. As an exaggerated example, I could not bring onto a plane a very light but long stick that is longer than the plane. I might be ok weight-wise but it could never fit into the plane. Fortunately the answer to this second concern is more easily and definitively determined.

3) My final concern was that Dr. Mercado might not give me straight answers to concerns 1 and 2. Don't get me wrong, I am not questioning his honesty and integrity, but I worry that since a second surgery on the same spot to further reduce the tumor is not advisable, then he might spare me any bad news on the two concerns if there were no definite way to "fix" any issues that might exist. Still, I went back to see him today one final time, wanting to ask him my nagging questions in person.

I came out of his clinic an infinitely happier man. I asked him two series of questions:

Q: Why does the tumor appear much lighter on the latest MRI?
A: (after explanations about blood supply and contrast dyes) Basically, there are much less living tumor cells within the tumor. The tumor is less dense.
Q: If it is less dense, given two tumors of identical sizes, one never-been-touched and the other already debulked via surgery, would it be fair to say that it will take less to kill the latter even though it is of the same volume as the former? Since it is less dense after having been "debulked".
A: That is absolutely correct.

This exchange pleased me no end, because it gives me some assurance that even if the volume of my remaining tumor is indeed right on the maximum of 3 cm, chances are very good that the radiosurgery will be successful because the tumor is now already easier to kill. Furthermore, even at 3cm, they will probably not even have to use maximum radiation dose. A "fresh" or "untouched" 3cm tumor is not the same as a 3cm tumor that resulted from debulking a larger tumor. Going back to our orange peel analogy, the peel left behind might still be 3cm in volume, but it is just peel, not strong and healthy orange.

Q: The 3cm theoretical maximum refers to total volume and doesn't mean that all sides must be smaller than 3cm, right?
A: Yes. We can tailor the beams to any size. The concern is that if the total volume is too large, then the required dose of radiation will be too high and will spill over to the healthy neural structures.

Another good answer!

Finally, I think Dr. Mercado saw through my questions to my actual concerns because he volunteered this statement: "With all credibility, honesty, and sincerity I say to you that your tumor is now ideal for gamma knife."

Here we go...