Biologically-guided and functional image-guided radiation therapy are changing how radiation oncologists treat cancer, said Theodore Lawrence, MD, PhD, during “Looking Beyond Anatomic-Based Treatment in Radiation Oncology,” the Annual Oration in Radiation Oncology at RSNA 2006 on Wednesday. Lawrence is chair of the radiation oncology department at the University of Michigan and professor in the department of environmental health at the university’s School of Public Health.
Advanced treatment planning and delivery systems allow radiation oncologists to treat tumors but save normal tissue with greater precision than could be imagined 20 years ago, Lawrence said.
Lawrence used intrahepatic cancer as an example since that has been the focus of his research. About 15,000 people die from primary and metastatic intrahepatic cancer every year, he said. Radiation hasn’t been used as a treatment therapy because of the liver’s low tolerance. However, certain parts of the liver can withstand high doses of radiation. So it becomes important to understand how much of the liver can be irradiated safely. The risks of liver radiation are overestimated, Lawrence said. He based a dose escalation trial on these ideas and found that increased doses of radiation to certain parts of the liver were “like surgery without a knife.” The survival rate at three years is about 25 percent which is much greater than the closer to zero percent survival rate before these trials, so they are showing progress, he said.
Lawrence said that tumors containing critical normal tissue do not respond well to high doses of radiation. A limited number of patients with tumors adjacent to normal tissue can benefit from high doses of radiation. With tumors inside critical structures, the goal is to ablate the tumor, Lawrence said. Stereotactic radiosurgery can treat brain metastases and small tumors can be approached with other therapies. No local treatment alone will address new metastases, he said.
To make the next leap, Lawrence said that we turn to biological and functional imaging both prior to and during treatment.
Lawrence discussed the results of hepatic perfusion and brain blood flow studies and how biomarkers can aid in treatment planning. For example, radiation-induced liver disease (RILD) occurs between two weeks and three months after treatment. It is caused by veno-occlusive disease. Dynamic contrast enhanced CT shows liver perfusion and can help clinicians gauge how occlusion and make adjustments in radiation treatment.
Research has shown that we can predict a patient’s response to treatment during treatment, rather than waiting weeks or months when it’s too late to make adjustments. Treatment based solely on anatomy means clinicians guess a dose based on hundreds of previous patients and base the risk of damage on the most sensitive five percent of the population. Now, treatment can be based on aberrant growth factor pathways and individual measurements. “Now we can adjust treatments during the course of treatment,” said Lawrence. A multimodality therapy approach keeps improving technology capabilities. Now we view cancer treatment in a much broader context, he said.
“Radiation oncology was born from radiology,” Lawrence said. The last 30 years were its adolescence, he added, and hopefully, over the next 30 years we will be working more closely together for further advances in cancer treatment.