Interfraction displacement of primary tumor and involved lymph nodes relative to anatomic landmarks in image guided radiation therapy of locally advanced lung cancer.
OBJECTIVE
To analyze primary tumor (PT) and lymph node (LN) position changes relative to each other and relative to anatomic landmarks during conventionally fractionated radiation therapy for patients with locally advanced lung cancer.


METHODS
In 12 patients with locally advanced non-small cell lung cancer PT, LN, carina, and 1 thoracic vertebra were manually contoured on weekly 4-dimensional fan-beam CT scans. Systematic and random interfraction displacements of all contoured structures were identified in the 3 cardinal directions, and resulting setup margins were calculated. Time trends and the effect of volume changes on displacements were analyzed.


RESULTS
Three-dimensional displacement vectors and systematic/random interfraction displacements were smaller for carina than for vertebra both for PT and LN. For PT, mean (SD) 3-dimensional displacement vectors with carina-based alignment were 7 (4) mm versus 9 (5) mm with bony anatomy (P<.0001). For LN, smaller displacements were found with carina- (5 [3] mm, P<.0001) and vertebra-based (6 [3] mm, P=.002) alignment compared with using PT for setup (8 [5] mm). Primary tumor and LN displacements relative to bone and carina were independent (P>.05). Displacements between PT and bone (P=.04) and between PT and LN (P=.01) were significantly correlated with PT volume regression. Displacements between LN and carina were correlated with LN volume change (P=.03).


CONCLUSIONS
Carina-based setup results in a more reproducible PT and LN alignment than bony anatomy setup. Considering the independence of PT and LN displacement and the impact of volume regression on displacements over time, repeated CT imaging even with PT-based alignment is recommended in locally advanced disease.
Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia.
Nuzhat
N
Jan
Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia.
Salim
S
Balik
Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia.
Geoffrey D
GD
Hugo
Department of Biostatistics, Virginia Commonwealth University, Richmond, Virginia.
Nitai
N
Mukhopadhyay
Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia. Electronic address: eweiss@mcvh-vcu.edu.
Elisabeth
E
Weiss
D059925:Anatomic Landmarks / Q000000981:diagnostic imaging*; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy; D054893:Cone-Beam Computed Tomography / Q000379:methods; D019583:Dose Fractionation, Radiation; D056973:Four-Dimensional Computed Tomography / Q000379:methods; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy; D008198:Lymph Nodes / Q000000981:diagnostic imaging* / Q000473:pathology; D009068:Movement; D011446:Prospective Studies; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D015203:Reproducibility of Results; D012119:Respiration; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging*; D013997:Time Factors; D047368:Tumor Burden / Q000528:radiation effects