Purpose: To determine the geometric accuracy of lung cancer radiotherapy using daily volumetric, cone-beam CT (CBCT) image guidance and online couch position adjustment.
Methods and materials: Initial setup accuracy using localization CBCT was analyzed in three lung cancer patient cohorts. The first (n = 19) involved patients with early-stage non-small-cell lung cancer (NSCLC) treated using stereotactic body radiotherapy (SBRT). The second (n = 48) and third groups (n = 20) involved patients with locally advanced NSCLC adjusted with manual and remote-controlled couch adjustment, respectively. For each group, the couch position was adjusted when positional discrepancies exceeded +/-3 mm in any direction, with the remote-controlled couch correcting all three directions simultaneously. Adjustment accuracy was verified with a second CBCT. Population-based setup margins were derived from systematic (Sigma) and random (sigma) positional errors for each group.
Results: Localization imaging demonstrates that 3D positioning errors exceeding 5 mm occur in 54.5% of all delivered fractions. CBCT reduces these errors; post-correction Sigma and sigma ranged from 1.2 to 1.9 mm for Group 1, with 82% of all fractions within +/-3 mm. For Group 2, Sigma and sigma ranged between 0.8 and 1.8 mm, with 76% of all treatment fractions within +/-3 mm. For Group 3, the remote-controlled couch raised this to 84%, and Sigma and sigma were reduced to 0.4 to 1.7 mm. For each group, the postcorrection setup margins were 4 to 6 mm, 3 to 4 mm, and 2 to 3 mm, respectively.
Conclusions: Using IGRT, high geometric accuracy is achievable for NSCLC patients, potentially leading to reduced PTV margins, improved outcomes and empowering adaptive radiation therapy for lung cancer.