A technique using a new form of surface imaging available at only one site in South Texas—the Cancer Therapy & Research Center (CTRC)—is expected to reduce women’s risk of long-term cardiac side effects from radiation therapy when treating left-sided breast cancer. The CTRC, part of the Health Science Center, is one of the state’s four National Cancer Institute-designated Cancer Centers.
The technique, called Deep Inspiration Breath Hold (DIBH), is performed in other Texas cities, but those centers do not offer the surface image-guided DIBH radiation delivery available at the CTRC, said radiation oncology physicist Alonso N. Gutiérrez, Ph.D., associate professor in the School of Medicine of the Health Science Center. The CTRC technique provides real-time verification of the breast position, ensuring proper separation between the breast and the heart. By only delivering the radiation when the breast is distanced away from heart with the expansion of the lung during a breath hold, the radiation dose to the heart may be minimized or eliminated.
“Conventional techniques of radiation therapy for left breast cancer give a dose of radiation close to the surface of the heart,” said CTRC radiation oncologist Richard L. Crownover, M.D., Ph.D., professor in the School of Medicine. “This is significant because coronary arteries are on the surface of the heart. The exposure may lead to small effects, basically acceleration of atherosclerosis or ‘hardening of the arteries.’ This becomes a small risk factor for heart attacks years later, especially for younger women.”
Deep Inspiration Breath Hold delivers a dose only when the lung is inflated and the heart is displaced. “This reduces radiation exposure to the coronary arteries, which is expected to reduce the risk of problems down the road,” Dr. Gutiérrez said.
“Increasing the margin of space between the coronary arteries and the radiation beam by even a fraction of an inch can greatly reduce this arterial exposure,” Dr. Gutiérrez said.
Only a handful of centers nationwide are starting to use the system that CTRC purchased. The CTRC’s configuration includes a positioning system that enables the treatment team to very accurately position the patient each time a treatment is done. They can position the patient into the same exact spot, to within a few millimeters, each day during a course of treatment.
“This is equivalent to lying down in your bed in the exact same position every night, to within a few millimeters,” Dr. Gutiérrez said.
The radiation is “gated”—the system does not allow the radiation beam except when the patient is in the correct deep breath hold position, Dr. Crownover said.
The patient wears goggles that visually indicate when to breathe. The patient sees a bar and a box in her field of vision, and when she breathes the bar goes up and down. The care team practices this with the patient at a “simulation” session prior to the start of treatment, Dr. Crownover said.