Symposium builds consensus for advanced radiotherapy

October 17, 2006

Varian Medical Systems is trying to build clinical consensus for image-guided radiotherapy as a tool for developing treatment regimens that increase the ratio of radiation dose to cancer as needed.

Varian Medical Systems is trying to build clinical consensus for image-guided radiotherapy as a tool for developing treatment regimens that increase the ratio of radiation dose to cancer as needed.

Globally, the company has installed more than 250 linear accelerators outfitted with the capability to perform image-guided radiotherapy. These IGRT systems are the means to implement dynamic adaptive treatment regimens that account for changes in the position of tumors moment to moment. Such changes can occur due to respiration and, over the course of the protocol, weight loss.

"Improvements in imaging technologies have enabled dramatic increases in the precision of radiotherapy treatments in recent years, allowing oncologists to adjust treatment plans based on daily imaging," said Rolf Staehelin, head of Varian's Oncology Systems marketing organization in Europe. "This has allowed them to boost doses, because they are more confident of being able to spare healthy tissue surrounding the tumor from any residual damage."

Varian is encouraging sites to gather research results to illustrate how its new technologies enable advances in patient care. During a symposium hosted by Varian Oct. 7 at the annual European Society for Therapeutic Radiology and Oncology meeting in Leipzig, Germany, oncologists from leading European research institutions bolstered this effort.

Dr. Robin Garcia, head of physics at Clinique Sainte Catherine in Avignon, France, presented the initial results of his team's project on the use of IGRT as dynamic adaptive radiotherapy for head and neck cancers. Daily imaging using the 3D kV conebeam CT mode on the Varian On-Board Imager enables automated repositioning of the treatment couch based on alterations between the image used to develop the plan and the newly acquired image, according to Garcia.

The ability to dynamically adapt treatment plans on a daily basis is vital because of variations in patient weight during the course of treatment. In the case of head and neck cancer patients, weight loss up to 20 kg may occur, resulting in the need to alter treatment plans. The technology has enabled new investigations in head and neck radiotherapy, he said.

Angela Heaton, a research radiographer at Clatterbridge Centre for Oncology in the U.K., outlined work using the radiographic, fluoroscopic, and kV conebeam CT imaging modes of the On-Board Imager. Among the new techniques initiated at Clatterbridge are a supine patient position for spinal and head and neck treatments, kV conebeam CT for verifying stereotactic radiotherapy treatments, and fluoroscopic imaging with Varian's RPM gating system to account for respiratory motion. IGRT has also proved useful in combination with seed markers for more tightly focused prostate treatments.

Staff at Rigshospitalet Copenhagen in Denmark have expanded the use of respiratory gating techniques beyond head and neck cancers. The Danish hospital uses respiratory gating to help treat breast cancer patients and is hatching plans to introduce similar treatments for lung patients. The patient is taught to breathe deeply using audio coaching. Physicians then time the radiotherapy to occur during maximum inspiration.

"This inflation of the lung anatomically separates the heart from the target tumor and reduces the amount of lung tissue in the fields," said Stine Korreman, Ph.D., of the radiation oncology department of the hospital's Finsen Center.

Using this method can reduce radiation dose to collateral lung tissue by 30% to 40%. The dose to the heart can be reduced by 80% to 90%, she said, with a corresponding decrease in the risk of complications such as pneumonitis and cardiac mortality.