Q: A 0.2 kilogram softball is thrown with a momentum of 3.1 kilogram- meters per second. What is the velocity of the softball?

It was in high school physics, solving these kinds of problems, that Charles Coffey, Ph.D., first found his calling. He remembers being thrilled to learn how the laws of physics explain the behavior of the world around us.

“I started problem solving in that class,” he says. “And I’m just as excited today about solving problems as I was then.”
The problems have gotten a bit trickier. Today, Coffey is the director of Medical Physics at the Vanderbilt Center for Radiation Oncology.

Medical physicists play a key, behind-the-scenes role in any diagnostic procedure or treatment that involves radiation, whether it’s conventional X-ray, CT imaging, or radiation therapy for cancer. Diagnostic physicists work with radiologists to capture the best images; therapy physicists, like Coffey, are the “pharmacists” of the radiation oncology team.

“The physician decides on a course of treatment and relies on medical physicists to help deliver that radiation prescription,” Coffey explains. “The physicist’s role is to determine – using everything from simple logic to very complicated calculations – how best to treat the tumor and spare the normal tissue.”

Coffey points to a computer screen showing a CT image of a tumor and nearby tissues. The tumor has a series of colorful lines around it that look like elevation lines on a topographic map and indicate the radiation dose. Getting these lines to match the tumor, “by varying the size and energy of the field, the radiation angles, and a lot of other things,” is part of treatment planning, Coffey explains.

Therapy physicists spend about 60 percent of their time involved in treatment planning. They spend the rest of their time assuring that every step of the process – “from A to Z,” Coffey says – is accurate.

They ask questions: Is the imaging study correct? Is the treatment planning algorithm correct? Are the machines (that deliver the radiation) calibrated? Is the delivery of the dose correct?

“Everywhere along the road there are quality assurance issues that we check routinely – some daily, some monthly, some annually,” he says.

While Coffey loves solving complex problems, he is perhaps even more excited about his role in training the next generations of medical physicists.

When Coffey came to Vanderbilt in 1993, the health and medical physics program that had been in place in earlier decades was inactive. With support from other faculty members, he helped revive the two-year master’s degree program, which now boasts 21 students. Plans to add a professional doctorate program await university approval. Vanderbilt would be the first institution to offer such a degree, which may be the way the field moves for training board-certified therapy physicists, Coffey says.

Another of Coffey’s joys – softball – has found its way into the medical physics program. Two teams with physics-inspired names – Accelerators and Electrons – are among the more competitive in Vanderbilt’s intramural system, and Coffey’s office has the framed championship shirts to prove it.

“The second question we ask students interviewing for the master’s program is whether they can play softball,” he says, laughing. He’s quick to add that softball skills are not a requirement for admission – just a penchant for solving problems (and the math and science background to go with it).

Having a homerun swing and a strong arm wouldn’t hurt though.

A: 15.5 meters per second – about 35 miles per hour – pretty fast for slow-pitch softball.

– by Leigh MacMillan

More information about the Vanderbilt medical physics master’s program at: www.vanderbilt.edu/msmp.