Saturday, July 6, 2013

Can't Help But Teach

For the past several years I have volunteered as a mentor for the high school robotics team in my town. I'm always trying to find examples of engineering and robotics-related careers to describe to the students to see if something sparks their interest. As I lay in the radiation treatment machine the other day it occurred to me that designing machines like that one would be cool and rewarding. I sent the following message to the team.

There's some repetition here from previous posts, but told a little differently.

The Engineers Who Are Saving My Life

Hi iRaiders Students,

A couple of months ago I was diagnosed with tongue cancer. It turns out the kind I have has a a very high cure rate so I'm confident that I'm going to be fine. Just some unpleasant treatment to go through to get there. Please don't worry. My family and I are being well taken care of by neighbors and family and I'm receiving excellent care at the Dana Farber Cancer Institute, one of the five best cancer centers in the country.

Part of my treatment is IMRT: Intensity-modulated Radiotherapy (commonly just called "radiation"). I will received a total of 35 radiation treatments. As I've watched the machine deliver the first few treatments, I thought it would be a great way to show students an example of how robotics and engineering skills can put you in a career where the products you design and build have a direct impact on people's lives.

First a little bit of biology. You probably know that every cell in your body contains your DNA. For cells to divide, they need to synthesize new DNA for the new copy (one cell is becoming two - each needs its own complete copy of your DNA). We all accumulate mutations in our DNA via several processes. Some mutations come from natural errors during replication. Other damage can come from chemicals in your diet or environment (e.g. cigarette smoke) and yet other damage can come from external sources like UV light from the sun. Cells can deal with a certain amount of DNA damage. For most types of simple damage, the cell has mechanisms that can repair the damage directly. If a cell accumulates too much damage to repair, then the cell will normally kill itself via a process called apoptosis.

Cancer is really a disease of the DNA. If the natural random mutations in a particular cell happen to occur within specific genes, the cell can become a cancer cell. The primary characteristic of cancer cells is that they grow and divide very quickly. That means even with a normal mutation rate of N mutations per cell division cancer cells accumulate more mutations at an accelerating rate. Some cancer cells also manage to turn off the "cell suicide" mechanism that would normally cause them to kill themselves when their DNA becomes so damaged.

Cancer treatments, both chemotherapy and radiation, work by inducing even more DNA damage. Chemotherapy induces DNA damage in all rapidly dividing cells, both normal and cancer. In my treatment, chemotherapy serves as a primer for radiation. Radiation, which is focused right on the tumor, amplifies the DNA damage inflicted by the chemotherapy. The cancer cells are overwhelmed by this double hit of DNA damage and they finally do kill themselves. It turns out normal cells can repair their radiation-induced DNA damage in about 6 hours but cancer cells cannot. That's why radiation is delivered every day for weeks (5 days per week for 7 weeks in my case). You keep kicking those cancer cells while they're down and eventually you kill all of them.

OK, enough of the biology, let's get to the technology.

I mentioned above that the radiation is focused on the tumor. That's important because doctors don't want to deliver radiation to healthy tissues that are adjacent to the tumor. That will damage those tissues, and in fact could lead to a future cancer. So engineers have developed ingenious ways to deliver radiation just to the desired areas.

The first step is to obtain calibration CT scans of the patient. This is a normal CT scan, but it is taken with the patient's body in a known position. The general classification for my type of cancer is "head and neck" (there are specialists in "head and neck cancer".) For a head and neck patient, they make a thermoplastic mask by pressing pliant plastic down over my head and shoulders and molding it to my anatomy. Once cured, this mask fastens to a plate that lies under my head and shoulders. When fastened, I cannot move my head. This helps ensure that the radiation is delivered to the same position in my body during every one of those 35 treatments.

Once they have made the mask and taken a CT scan of me in it, the doctors can perform "radiation planning". The first step is to do some CAD-like work. A CT scan is like a stack of x-rays that are slices through the patient. Think of my neck and head as a stack of plates where each plate is an x-ray image of the part of my head the plate passes through. The doctors can use a digital pen to draw outlines of anatomical structures on each layer of the image (each plate). In my case they outlined the tumor, the nearby lymph nodes, the esophagus, carotid arteries, important nerves, my spine, my jaws and teeth, etc. Once you have those outlines in each layer, you can connect the outlines to create 3D volumes that represent those structures. Now you have what looks like a 3D CAD drawing of the inside of my head and neck. Here is an example of what that might look like:

Now the doctors (called Radiation Oncologists - cancer doctors who treat with radiation) perform the real planning. They design a series of x-ray beam angles and shapes to "paint" the tumor with high radiation doses while delivering very low doses to healthy tissues very nearby. They use special software to design a treatment program, and it includes a simulator that will compute the dose delivered to any given area. They can tweak the plan until the have exactly the dose delivery pattern they want.

This is where the technology comes in that is similar to robotics. The Radiation Oncologists have to design the treatment program within the contraints of the machines that will deliver the radiation. Those machines provide several clever ways to shape the x-ray beam. There are interchangeable lenses that shape the beam as a cone, cylinder, etc. But the coolest part is called the collimator. Here's a brief video of a collimator in action:

In the video the radiation is passing through the hole. Notice how the shape of the hole can be infinitely customized. In fact, in real treatment, the hole "moves" across the beam and changes shape as it does so. By watching the collimator, I can see the shape of the target area in my neck.

Here's a picture of the machine I am being treated on, a Novalis Tx:

The linear accelerator that produces the x-rays is in the top part. The yellow ring holds the focusing lenses and the collimator (which is visible through the glass window). As you can see, the entire machine rotates on a horizontal axis. The yellow head also rotates so that the collimator can be oriented differently to the beam. And finally the patient table can rotate and tilt to customize the patient position.

Once the treatment planning is done at the beginning of treatment, the actual treatment delivery is completely automatic. When I go in for daily treatment, the technicians position me with my mask. The machine then takes a normal x-ray which is used to make sure my position is aligned with the reference position used for planning. Then the treatment program is started by the technicians and it runs through all of the positions automatically. I keep losing count, but my program has about 15 different positions and exposures. It lasts about 15 minutes.

So why did I write this long message to you? If you are interested in engineering, this is a type of work you could do. It was engineers who designed that machine. One set of engineers designed the overall chassis and the big rotational system. Another group designed the x-ray source and path. And yet another group designed the focusing and beam-shaping system. All of them had to work within very exact tolerances and with some extremely stringent safety constraints - the last thing you want this machine to do is deliver too much radiation to a patient, or to the wrong location.

I work for a company that makes medicines. I can speak from experience that working for a company that has a direct impact on peoples' health provides an extra measure of motivation and reward. The engineers who designed this machine can take pride in the fact that their work is literally saving my life.

A similar machine is made by Varian, the company Mr. Holden works for.

P.S. If you have the patience to listen to the narrator speak very slowly for 5 minutes, this video (about the Varian machine) is even more informative about how IMRT works.


  1. Awesome idea! I would bet money that this email will shape more than one of their life paths

  2. Being a teacher myself, I think you did great in focussing your message on the target audience. It is clear that you love explaining things to people, and you appear to be good at it!