[Scope and method of image registration and clinical target volume margin for central-type non-small cell lung cancer in image-guided radiotherapy].

OBJECTIVE: To determine the influence of different registration scopes and methods on kilo-voltage cone beam CT (kVCBCT) image and CT image and to estimate the appropriate clinical target volume (CTV)-to-planned target volume (PTV) margin for central-type non-small cell lung cancer in image-guided radiation therapy (IGRT). METHODS: Twenty-six patients with central-type non-small cell lung cancer (NSCLC) who received IGRT were enrolled in this study and totally 104 flames of kVCBCT scanning acquired before radiotherapy were analyzed. First, registrations were performed by gray plus manual match and were compared among different registration scopes of tumor and tumor plus vertebra. Then, the results of registration as well as time cost using tumor plus vertebra as registration scope were compared among different registration methods of gray plus manual match and bone plus manual match. At last, 200 registrations using tumor plus vertebra as the registration scope performed by bone plus manual match were recorded and the CTV-to-PTV margin was calculated. RESULTS: There was no significant difference in X, Y and Z translational and rotational movements between the registration scopes of tumor and tumor plus vertebra when gray plus manual match was used as the registration method (P>0.05). The registration results of gray plus manual match and bone plus manual match were equal when tumor plus vertebra was used as the registration scope (P>0.05), but the time cost of bone plus manual match [(1.9±0.3) min] was shorter than that of gray plus manual match [(3.1±0.2) min]. The CTV-to-PTV margins were 5.3, 4.9 and 5.7 mm in X, Y, and Z directions respectively. CONCLUSION: For central-type NSCLC, tumor and vertebra can be used as registration scope and the bone plus manual match is suggested in IGRT. To avoid errors, we suggest a CTV-to-PTV margin of 6 mm.