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

Abstract

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 ± 3.5 mm (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 ± 2.5 mm (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.