Taking aim at cancer

A UVic physicist seeks to improve the accuracy of radiation therapy

by Shannon McCallum

Jirasek, with a linear accelerator used for radiation therapy.

Anyone who has had radiation therapy for cancer, or has seen relatives or friends go through it, knows how unpleasant the side effects can be.

UVic's Dr. Andrew Jirasek wants to change that. As a medical physicist he studies how radiation interacts with biological materials, and his goal is to make radiation therapy a more accurate, effective and less debilitating tool for treating cancer patients.

Radiation therapy is used in about half of all cancer cases. It works by destroying the genetic material of tumour cells, preventing them from replicating and causing the tumour to shrink or disappear. Side effects—such as fatigue, nausea, hair loss and skin irritation—occur when the radiation damages surrounding healthy cells and tissue.

The goal of improved radiation therapies is to maximize damage to cancer cells while minimizing damage to the surrounding healthy cells and, consequently, limiting the side effects.

"This is easier said than done," says Jirasek. "We know that different organs and tissues tolerate different amounts of radiation. Add to this that tumours tend to be oddly shaped, and the task of targeting cancerous tissue with the proper dose while avoiding healthy tissue can be a challenge."

Modern radiation techniques are now sophisticated enough to deliver radiation that conforms to the complex, three-dimensional shape of tumours. This helps reduce the dose to healthy tissue and minimize side effects.

"What we can't do as well is confirm, by measurement, how well the radiation doses have hit their intended mark," says Jirasek. "This creates some uncertainty about exactly where the radiation has been deposited."

To reduce this uncertainty, Jirasek is collaborating with researchers at the BC Cancer Agency's Vancouver Island Centre, where he recently set up one of his two new research labs. Their project uses jelly-like substances that absorb radiation in the same way as human tissue.

These "gel dosimeters" also include special materials that form distinctive molecules when hit by radiation. By counting the number of molecules formed after a dose of radiation, Jirasek and his colleagues can measure the exact amount of radiation absorbed.

"The therapeutic benefit is that treatment plans and doses can be verified more quantitatively," says Jirasek. "It will allow us to say with more confidence that the dose we think we're giving is actually what the patient is receiving".

Jirasek's lab is also working on research to personalize radiation doses. "Two people of the same age and gender with the same type of cancer and similar-sized tumours can respond very differently to the same dose of radiation," he explains.

Since DNA is what makes individuals unique, it could help explain these variations. To find out, Jirasek has developed a method that monitors changes in the molecular structure of DNA as it's bombarded with varying doses of radiation.

"We've taken radiation therapy to a point where it is very effective, but the doses we use are conservative ones based on population statistics," says Jirasek. "Now we want to personalize treatments for individual patients, organs and tissues. That's where the next wave of radiation therapy research is headed."