Radiation oncology has witnessed rapid progress in recent decades, as technological advances have made it possible for physicians to deliver increasingly targeted and powerful doses of radiation to treat cancers.

But one challenge remained — knowing precisely where the tumor stops and healthy tissue starts during radiation treatment. On Dec. 3, a crane carefully dropped a 9,000-pound solution to this problem through the roof of the UC Davis Cancer Center's Radiation Oncology Clinic. The $3 million tomotherapy unit represents a new generation in radiation therapy technology.

Only unit in Northern California

Since first reaching the market in 2002, seven tomotherapy systems have been acquired on the West Coast: one in Bellingham, Wash., and five in Southern California. UC Davis has the only tomotherapy unit between Los Angeles and Seattle. Only 43 of the machines are in use worldwide. UC Davis Cancer Center hopes to begin offering tomotherapy to patients this spring.

"We can now offer our patients more treatment options than any other cancer center in our region," said Srinivasan Vijayakumar, professor and chair of radiation oncology at UC Davis.

Reduced margin of error

Traditionally, a radiation oncologist obtains sophisticated CT images of a tumor days or weeks before radiation therapy starts. These images are used to guide development of a detailed treatment plan. But by the day of treatment, the cancer may have grown or changed shape, or the patient's weight may have changed, causing a shift in tumor position. Some linear accelerators are equipped with an X-ray, but one-dimensional X-rays can't provide the same level of detail as a three-dimensional CT study.

"This uncertainty about the tumor's exact position has always meant calculating a 'margin of error' and treating a zone around the tumor that is likely to include some healthy tissue. To avoid applying excessive radiation doses to this surrounding tissue, radiation oncologists have had to use lower-than-desired doses to treat the tumor," Vijayakumar said.

Higher doses

Tomotherapy solves this problem by marrying a high-resolution CT scanner to a sophisticated linear accelerator, allowing doctors to visualize a tumor and apply radiation at the same time, with pinpoint accuracy. This enhanced precision enables doctors to use tighter margins and higher, more effective radiation doses.

In addition, tomotherapy employs a linear accelerator that rotates in a 360-degree spiral around the patient, delivering radiation to the tumor from all directions. Traditional linear accelerators deliver radiation beams from just a handful of angles. Tomotherapy systems are marketed by TomoTherapy, Inc., in Madison, Wis.

$6 million expansion

The new technology is part of an ambitious, three-year expansion of the Radiation Oncology Clinic and Department of Radiation Oncology spearheaded by Vijayakumar, who joined UC Davis from the University of Chicago in 2002. The expansion includes the recruitment of five new radiation oncology faculty physicians and physicists, along with the completion last year of a $6.1 million, 7,000-square-foot addition to the Radiation Oncology Clinic, located at 4501 X Street on the UC Davis Medical Center campus.

In addition to the tomotherapy system, UC Davis Cancer Center last summer acquired another system, a $1.9 million Elekta Synergy that combines an advanced linear accelerator with three-dimensional X-ray technology. The linear accelerator in the Synergy system doesn't rotate around the patient. But unlike tomotherapy, the Synergy machine can tailor radiation energy levels to a tumor's location and shape.

Cranial radiosurgery

UC Davis Cancer Center also offers patients two technologies for cranial radiosurgery: a Leksell gamma knife and a BrainLab micro multileaf collimator. The BrainLAB system can treat larger, irregular lesions, while the gamma knife can treat smaller tumors. UC Davis is the only institution in the Sacramento region and one of a small number in the country to offer both cranial radiosurgery options.

"No single technology is best for every patient," Vijayakumar said. "But by having more of the latest tools at our disposal, we are able to offer patients more choices to fight their disease."