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

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.

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.

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.

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.