Evaluation of the geometric accuracy of anatomic landmarks as surrogates for intrapulmonary tumors in image-guided radiotherapy.
OBJECTIVE
The purpose of this study was to evaluate the geometric accuracy of thoracic anatomic landmarks as target surrogates of intrapulmonary tumors for manual rigid registration during image-guided radiotherapy (IGRT).


METHODS
Kilovolt cone-beam computed tomography (CBCT) images acquired during IGRT for 29 lung cancer patients with 33 tumors, including 16 central and 17 peripheral lesions, were analyzed. We selected the "vertebrae", "carina", and "large bronchi" as the candidate surrogates for central targets, and the "vertebrae", "carina", and "ribs" as the candidate surrogates for peripheral lesions. Three to six pairs of small identifiable markers were noted in the tumors for the planning CT and Day 1 CBCT. The accuracy of the candidate surrogates was evaluated by comparing the distances of the corresponding markers after manual rigid matching based on the "tumor" and a particular surrogate. Differences between the surrogates were assessed using 1-way analysis of variance and post hoc least-significant-difference tests.


RESULTS
For central targets, the residual errors increased in the following ascending order: "tumor", "bronchi", "carina", and "vertebrae"; there was a significant difference between "tumor" and "vertebrae" (p=0.010). For peripheral diseases, the residual errors increased in the following ascending order: "tumor", "ribs", "vertebrae", and "carina". There was a significant difference between "tumor" and "carina" (p=0.005).


CONCLUSIONS
The "bronchi" and "carina" are the optimal surrogates for central lung targets, while "ribs" and "vertebrae" are the optimal surrogates for peripheral lung targets for manual matching of online and planned tumors.
Department of Radiation Oncology, Cancer Hospital and Institute, Tianjin Medical University, Tianjin, China.
Hong-Sheng
HS
Li
Ling-Ling
LL
Kong
Jian
J
Zhang
Bao-Sheng
BS
Li
Jin-Hu
JH
Chen
Jian
J
Zhu
Tong-Hai
TH
Liu
Yong
Y
Yin
D000230:Adenocarcinoma / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D059925:Anatomic Landmarks; D001980:Bronchi / Q000473:pathology; D018287:Carcinoma, Large Cell / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography; D005500:Follow-Up Studies; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D009367:Neoplasm Staging; D011379:Prognosis; D011880:Radiotherapy Planning, Computer-Assisted; D061089:Radiotherapy, Image-Guided; D012189:Retrospective Studies; D055752:Small Cell Lung Carcinoma / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*