Motion Analysis of 100 Mediastinal Lymph Nodes: Potential Pitfalls in Treatment Planning and Adaptive Strategies
Received 15 May 2008; received in revised form 27 July 2008; accepted 28 September 2008. published online 18 December 2008.
Purpose
The motion of mediastinal lymph nodes may undermine local control with involved-field radiotherapy. We studied patterns of nodal and tumor motion in 41 patients with lung cancer.
Methods and Materials
Four-dimensional (4D) computed tomography planning scans were retrospectively evaluated to identify patients with clearly visible mediastinal lymph nodes. One hundred nodes from 14 patients with Stage I and 27 patients with Stage III were manually contoured in all 4D computed tomography respiratory phases. Motion was derived from changes in the nodal center-of-mass position. Primary tumors were also delineated in all phases for 16 patients with Stage III disease. Statistical analysis included a multivariate mixed-effects model of grouped data.
Results
Average 3D nodal motion during quiet breathing was 0.68 cm (range, 0.17–1.64 cm); 77% moved greater than 0.5 cm, and 10% moved greater than 1.0 cm. Motion was greatest in the lower mediastinum (p = 0.002), and nodes measuring 2 cm or greater in diameter showed motion similar to that in smaller nodes. In 11 of 16 patients studied, at least one node moved more than the corresponding primary tumor. No association between 3D primary tumor motion and nodal motion was observed. For mobile primary tumors, phase offsets between the primary tumor and nodes of two or more and three or more phases were observed for 33% and 12% of nodes, respectively.
Conclusions
Mediastinal nodal motion is common, with phase offsets seen between the primary tumor and different nodes in the same patient. Patient-specific information is needed to ensure geometric coverage, and adaptive strategies based solely on the primary tumor may be misleading.
∗Department of Radiation Oncology, VU University Medical Center, Amsterdam, The Netherlands
†Biometrics Department, Netherlands Cancer Institute, Amsterdam, The Netherlands
Reprint requests to: Suresh Senan, M.R.C.P., F.R.C.R., Ph.D., Department of Radiation Oncology, VU University Medical Center, De Boelelaan 1117, 1007 MB, Amsterdam, The Netherlands. Tel: (+31) 20-444-0414; Fax: (+3) 20-444-0497
Research funding for J.R.P. has been provided by the Canadian Association of Radiation Oncology in partnership with Elekta and the University of Ottawa.
Accepted for presentation at the 50th Annual Meeting of the American Society for Therapeutic Radiology and Oncology (ASTRO), September 21–25, 2008, Boston, MA.
ABSTRACT