NEW YORK (MedscapeWire) Jan 08 — When people with lung cancer are treated with radiation therapy, the size of their tumor may be the best predictor of the treatment's success, rather than how far the tumor has spread within the lung.

This finding by researchers at Washington University School of Medicine in St. Louis, Missouri, is published in the January issue of the International Journal of Radiation Oncology, Biology and Physics.

The study sought to identify the best predictor of therapeutic outcome for patients treated with 3-dimensional conformal radiation therapy (3D-CRT), the state-of-the-art in radiation therapy for lung cancer. Three-dimensional conformal radiation therapy uses computers to shape the radiation beam so that as little healthy tissue as possible is damaged during the treatment.

Physicians typically try to gauge the likely success of radiation therapy for lung cancer based on whether the cancer has spread to lymph nodes or other tissues. Such factors determine the tumor's stage.

"Cancer staging has been used to predict treatment outcome for patients with every kind of cancer and is useful for people undergoing surgery," says Jeffrey D. Bradley, MD, associate radiation oncologist at Washington University's Mallinckrodt Institute of Radiology and the study's lead author. "But for a lung cancer patient whose tumor isn't treated with surgery, the traditional staging system may not be the right approach. Our findings suggest tumor volume is more important."

The retrospective study looked at data from 207 patients with an average age of 66 years who were treated at Washington University for inoperable non-small cell lung cancer between March 1991 and December 1998. All patients had undergone treatment with 3D-CRT, which requires careful visualization of the tumor in 3 dimensions prior to treatment.

The investigators identified a variety of factors thought important for predicting treatment outcome after radiation therapy. Their analysis included patient characteristics such as age, sex, and race; tumor characteristics such as clinical stage, tumor stage, and tumor type; and treatment parameters such as radiation dose, whether a patient was treated with chemotherapy, and the gross tumor volume as determined by computed tomography (CT) scans using 3D-CRT treatment planning technology. Gross tumor volume refers to the total size of the tumor, which includes the lung tumor itself plus the affected lymph nodes.

"When we analyzed the data," says Bradley, "characteristics such as age, tumor stage and whether or not the patient got chemotherapy all dropped out. The most important factor was gross tumor volume."

The average survival for all 207 cases, or all tumor sizes combined, was 59% after 1 year and 41% after 2 years.

When the researchers looked at survival according to tumor size, they found that patients with small tumors — tumors equivalent to 3 cubic centimeters or smaller — did much better than those with larger tumors: 68% of patients with small tumors survived after 1 year and 61% survived after 2 years, whereas only 44% of patients with large tumors survived more than 1 year and 25% survived more than 2 years.

Many of these patients also suffered from other serious illnesses such as heart disease, lung disease, and diabetes. When the researchers looked at people who died because of their tumors and not from other causes, survival rates for patients with the smallest tumors were 78% at both year 1 and 2. Tumor-specific survival rates for those with the largest tumors were 51% after the first year and 29% after the second year.

The findings suggest that 3D-CRT may be an alternative for patients with small tumors who ordinarily would be treated with surgery but for whom surgery is hazardous. For example, an elderly lung cancer patient whose advanced age or additional chronic illness would make surgery difficult to tolerate might be a good candidate for 3D-CRT.

The findings also suggest that patients with large tumors should be treated less aggressively, according to Bradley. "These patients may be better treated with lower doses of radiation to help control their symptoms rather than large doses that try to eliminate the tumor."

But before such recommendations can be made, Bradley cautions, "our findings must be confirmed in a large multi-institutional study."