Doctors at the Sierra Nevada Memorial Hospital Cancer Center have been using scanners to produce 3-D images of the body for many years. But now they’ve entered the fourth dimension — imaging that is able to track the movement of tumors and surrounding organs as the body breathes.
Known as 4-D CT scanning, the technology is now in use and helps a doctor aim healing beams of radiation more accurately, according to Dr. David Kraus, medical director of the Department of Radiation Oncology at Dignity Health Sierra Nevada Memorial Hospital.
“Tumors are scanned in relation to how the patient breathes,” Dr. Kraus explained. “The radiation treatment is then delivered based on the pattern of the tumor motion as it varies with breathing. Our new linear accelerator has software to track this breathing motion and confirm the treatment is delivered as planned.”
As an example, a tumor in the lung moves as the lung expands and contracts with patient breathing. Before 4-D imaging was developed, radiation oncologists could only target that tumor where it would be at one moment during the breathing process. The beam only hit at that point and could miss if there was irregular breathing, possibly damaging surrounding healthy tissue. Lower doses were used to keep potential damage to a minimum.
By knowing and tracking the patient’s breathing pattern through 4-D scanning, the oncologist can design a treatment that will target the tumor and deliver the radiation in harmony with the breathing cycle. Thus, the tumor is being treated at all positions within that cycle. This makes delivery more accurate and reduces chances of harming surrounding tissue.
Thanks to 4-D imaging, Dr. Kraus said “high dose, highly focused treatments can be delivered in five treatments with higher cancer control and fewer side effects.”
“For medically inoperable early stage lung cancer patients, cure rates similar to surgery can be achieved,” he added.
The 4-D technology was introduced at the center in December, and has been used on three patients so far. In all three cases, Dr. Kraus said 4-D simulations were accurate and reproducible.
The 4-D simulations are an integral part of the center’s Stereotactic Ablative Body Radiotherapy (SABR) program, Dr. Kraus said. SABR is a radiation delivery system that employs smaller, thinner beams of radiation simultaneously from different angles. The effect is that the tumor receives the accumulated strong dose while the individual beams carry only low doses through surrounding tissue.
The center is now treating about a dozen lung cancer patients annually, Dr. Kraus said. But as experience is gained with these patients, Dr. Kraus predicted that in coming years it will also be used to treat patients with cancers in the liver, pancreas and spine.
Before the Cancer Center acquired the 4-D technology, patients from the Grass Valley/Nevada City area had to be referred to regional medical facilities.
“Our hospital has made a commitment to deliver the same quality of radiation care locally for which patients previously had to travel long distances,” Dr. Kraus explained. “Any small community like ours may possess the equipment, but they need to have the knowledge and willingness to use it. We do.”
Community support for new medical technology is a vital part of the equation, Dr. Kraus acknowledged.
“This new capability was made possible with the new linear accelerator we installed in 2011,” he said. “Without the hospital foundation’s fundraising efforts, and donations from our community, we would not have a new linear accelerator or a 4-D simulator.”
All physicians providing care for patients at SNMH are members of the medical staff and are independent practitioners, not employees of the hospital.