The Impact of Evolving Image-Guidance Processes on Initial Patient Setup for Lung Radiotherapy

Purpose: The purpose of this study was to investigate whether the implementation of three different daily image-guidance processes has altered initial (pre-imaging) patient setup practice for thoracic radiotherapy patients. Methods: A total of 1 997 daily cone-beam computed tomography (CBCT) images from 72 thoracic patients undergoing radical radiotherapy were retrospectively reviewed under ethics approval. Patients were analyzed in three consecutive cohorts grouped according to the image-guidance process used during radiotherapy. After initial alignment of skin marks and lasers: Process A (24 patients spanning 6 months), CBCT alignment with an action level of 3 mm, correction applied via manual couch adjustment, followed by a verification CBCT; Process B (22 patients, 5 months), CBCT alignment with an action level of 3 mm, correction applied via remote couch adjustment, followed by a verification CBCT; Process C (26 patients, 5 months), CBCT alignment with correction applied for all displacements via remote couch adjustment, with no verification scans required. Initial patient setup displacements from skin marks were determined by re-registering the initial alignment CBCT to the planning CT using automated spine matching. Patient setup displacements were compared between the three processes in the left-right (LR), cranial-caudal (CC), and anterior-posterior (AP) directions. Results: The mean +/- 1 standard deviation of initial patient setup displacements were calculated for each cohort: Process A, 1.2 +/- 2.4 mm (LR), 0.6 +/- 3.5mm(CC), and -0.8 +/- 2.0 mm(AP); Process B, 0.5 +/- 2.7 mm (LR), 1.2 +/- 3.4 mm (CC) and -1.7 +/- 2.0 mm (AP); Process C, 1.0 +/- 2.5mm(LR), 0.1 +/- 3.5 mm(CC), and -2.3 +/- 2.2 mm(AP). The means systematic and random uncertainties were comparable between the processes, showing similar setup error distributions. Conclusion: Initial skin setup practices for thoracic radiotherapy patients remain unaffected across the three image-guidance processes. Pre-imaging alignment principles and performance by radiation therapists at our center remain consistent amid technological advances.