Purpose: Knowledge of changes in gross tumor volume (GTV) and of GTV motion during a course of radiotherapy is necessary for accurate treatment delivery. This study describes the time trends in nodal computed tomography (CT) volume and motion for patients with locally advanced non-small-cell lung cancer (NSCLC).
Patients and methods: In a prospective clinical trial, 12 patients with a total of 22 positive nodes underwent a CT-positron emission tomography scan before treatment, as well as in the first and second week following start of radiotherapy. Volume changes could be measured for all nodes. For 21 nodes, the motion was measured on the basis of a respiration correlated CT (RCCT) scan. Repeated RCCT scans were available for 11 nodes to evaluate the change in motion.
Results: In 6 of 22 (27%) patients, the nodal volume increased >30%, whereas in 3 of 22 (14%) the volume decreased >30%. On average, the nodal volume did not change significantly (from 4.9 to 5.1 to 4.6 cm(3)). The average motion of the nodal areas was initially 5.6 +/- 2.8 mm. This motion decreased slightly during therapy but not statistically significant. However, large interpatient and internodal motion differences were observed.
Conclusion: A large variability of changes in nodal volume between patients was observed. However, this had limited clinical impact because volumes and hence volume changes were small. The nodal motion did not change significantly during therapy. However, because of the large interpatient variability of nodal motion before treatment, internal margins for nodal areas should be calculated before radiotherapy using RCCT, such that the margins can be applied for individual patients. Repeated imaging of the nodes seems however to be of limited use because the observed individual changes in nodal volume and motion tend to fall within the commonly applied margins.