Pain in Nick's A**: Radiation Therapy

So lets talk about radiation therapy. Why radiation therapy? Because I think it's kind of cool. Well the radiation portion isn't that cool, it's pretty straight forward. Shoot tumor with radiation, tumor starts to die. Simple right. The trick is how to deliver the radiation dose to the tumor while trying to spare the surrounding tissue as much as possible. There are some things that's you'd rather not shoot with radiation if you don't have to. Those of us of child bearing age, would prefer to keep the family jewels intact. The bladder and prostate seem to be important things, shooting them with radiation is probably not a good idea. With that said, the cancer will kill you dead, so maybe a little radiation damage to the prostate is acceptable. But how do you minimize the damage to the surrounding tissues, while providing enough of a kill shot to the tumor?

Radiation therapy it the medical use of ionizing radiation to damage the DNA of the cancer cells so that they die and/or slow the reproduction. In the old days, the machines typically shot radiation in 4 directions. They'd shoot you from A (anterior) to P (posterior) (front to back). Then they moved the machine 90 degrees and shoot laterally across your body. Then move the machine 90 more degrees and shoot P to A (back to front) and finally move another 90 degrees and shoot you laterally the other direction. The problem with this is you only distribute the radiation dose across 4 different shots, so a higher radiation dose is delivered to healthy tissue. The dose distribution map for this older method, below.

Conformal Radiotherapy dose distribution field

The next advance seems to have come from IMRT (Intensity Modulated Radiation Therapy) The idea here is not only does a patient get shot at from more angles, but the beam is also modulated in shape to more precisely target the tumor. The dose distribution map for this method, below.

 IMRT dose distribution field

As you can see from the above two fields the IMRT targets the tumor more precisely and while more healthy tissue gets radiated, it is getting a much smaller percentage of the total dose. The below video does a good job explaining IMRT and how the 'shutters' shape the dose.

IMRT Video

They have now taken it a step further. If multiple beams are better why not just shoot radiation at the tumor while the 'gun' is dynamically moving around the patient. This is a technology developed by a local Bay Area company called Varian Medical Systems and they call the technology Rapid Arc. It basically allows more precise targeting with more healthy tissue being spared. Below is a quick video describing it.

Rapid Arc Video

I'm being treated on a Varian Clinac 21EX with all of the upgrades. The upgrades include Rapid Arc as well as an on-board imaging system capable of both x-rays and CT scans. Below is a picture of the machine that's doing the work.

Varian Clinac 21EX at the Stanford Cancer Center

My treatments start out by me lying on the couch (bed with the sheet), then the techs position me by moving both me and the couch (couch is capable of moving in 3 directions and rotation in one) to align the tattoos on my torso (yes, I have some tats now cause I'm hard core...actually just three <1mm dots) with lasers. Below is a pic of me in position.

Positioned and ready to go

Once positioned on the couch everyone except me leaves the room. The techs proceed to take both an A-P and a lateral x-ray. On Mondays they also include a CT scan. After the scans are taken they make some final adjustments (adjustments are made to 0.1cm or 1mm) to my location and the treatment starts. The treatment lasts about 2 minutes as the 'gun' encircles me twice (I don't feel a thing as they're shooting me), then I'm done. The daily radiation dose is 2 Gy for a total of 50 Gy for all 25 days. The whole appointment from when I'm called back to finished is probably less than 10 minutes.