Use of surface tracking recordings to identify pitfalls during surface-guided radiotherapy

The precise daily positioning of patients during radiation therapy determines the quality of the entire treatment. To avoid additional radiation exposure from regular cone-beam CT (CBCT) scans, surface-guided radiotherapy systems (SGRT) are increasingly used. The aim of this prospective clinical study was to evaluate the advantages, feasibility, and pitfalls of SGRT using the surface tracking recorder prototype of the camera component of ExacTrac Dynamic (Brainlab AG, Munich, Germany). This system combines both surface-based imaging technology and a thermographic camera that records patients via thermal imaging to accurately measure patient geometry.

The surfaces of patients with various tumor entities and therefore different regions of interest (ROIs) were recorded with the surface camera during positioning and throughout treatment. Subsequently, these surface camera datasets were analyzed to compare the accuracy of patient positioning with the current treatment standard (X-ray-based IGRT). The camera components were used only as an imaging tool and not to correct any deviations. For evaluation of typical pitfalls, errors > 5 mm for extracranial indications and > 2 mm for cranial indications were analyzed using parameters extracted from the surface recordings and the corresponding CBCT shifts.

In total, 162 displacement vector datasets for 130 patients were generated and evaluated. The smallest deviations were found in the head and neck regions (mean deviation 1.9 mm/0.8°). The largest mean translational deviation (4.8 mm) and mean rotational deviation (1.1°) were found in the pelvic area. In all regions, most datasets showed clinically acceptable deviations; however, large outliers were observed in some measurements, particularly longitudinally. These outliers are of special interest because they may indicate mistakes in the use of SGRT, and they were therefore analyzed separately in detail. Several reasons for the outliers were identified, and potential solutions to avoid these pitfalls are presented.

This observational study demonstrated the advantages and pitfalls of SGRT by using the surface tracking recorder prototype of the camera component of ExacTrac Dynamic. These pitfalls can be avoided through thorough application of SGRT. This study may serve as a practical guide for clinicians already using or introducing SGRT for patient positioning.