New Techniques Help Doctors Precisely Target Cancer Cells

When it comes to treating cancer with radiation, the key to success is precision.

"You want to hit the tumor — the bulls-eye if you will — as precisely as possible and avoid the healthy tissue surrounding it," says Dr. Erik Assarsson, a radiation oncologist at Bryn Mawr Hospital. "With radiation therapy, the better your aim, the higher the dose of radiation you can give and the better the cure rate."

Hitting the bulls-eye has gotten a lot easier in recent years thanks to two relatively new techniques: Image Guided Radiation Therapy (IGRT) and Stereotactic Radiosurgery.

IGRT, which is often used to treat prostate cancer, delivers high doses of radiation directly to cancer cells in a very targeted way, much more precisely than is possible with conventional radiotherapy.

"In the past, radiation therapy took a 'shotgun' approach, radiating a larger area than necessary just to be sure we hit the whole tumor," says Dr. Assarsson. "IGRT takes a laser approach, honing in on a tumor while sparing healthy tissue around it."

IGRT is made possible thanks to the combination of advanced imaging techniques and improvements in how radiation is delivered. Taken together, doctors can now "paint" a precise radiation dose to the tumor — even irregularly shaped tumors — and adjust treatments to increase the chances of eradicating the tumor and minimizing side effects.

"Today we can produce high-resolution, three-dimensional images to pinpoint tumor sites," says Dr. Assarsson. "These images also allow us to track changes in tumor shape, size or position over a multi-week course of treatment."

In addition to IGRT, doctors at Bryn Mawr Hospital are using stereotactic radiosurgery, another highly precise form of radiation therapy used primarily to treat tumors and other abnormalities in the brain.

Despite its name, stereotactic radiosurgery does not involve any open surgery. Instead, it's a method of delivering a single high dose — or sometimes smaller, multiple doses — of radiation beams that converge on the specific area of the brain where the tumor or abnormality resides.

"What we're doing is using the radiation beam like a scalpel but without actually cutting into the patient," says Dr. Assarsson.

Stereotactic radiosurgery uses a helmet-like device to keep a patient's head completely still and three-dimensional computer-aided planning software to map the location of the tumor. This precision minimizes the amount of radiation to healthy brain tissue.

"If cancer cells came in a Petri dish these precision techniques wouldn't be needed because we could just radiate the entire dish," says Dr. Assarsson. "But cancer occurs in the human body, and we want to do everything possible to precisely hit the target and spare healthy tissue."