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Surface Guided Radiotherapy (SGRT) in new, non-invasive technique for patient positioning and monitoring which uses visible light for position determination and helps reduce daily imaging. In this study, we assess the role SGRT in setup uncertainties and intrafraction motion with standard practices.

Between January 2021 and October 2021, a total of 25 patients with histopathologically proven breast cancer who were treated with radiation therapy were enrolled and planned for SGRT-based setup. The comparison was done with similar cohort of patients who were positioned by aligning skin markers to the room lasers (Laser-based setup - LBS). The surface-based setup (SBS) included an optical surface scanning system which was used for daily setup and the intrafraction movements were accounted. In initial setup, SGRT was compared to three‐point setup using tattoos on the patient and cone-beam computed tomography (CBCT). 

Among the 25 patients evaluated, median time for SBS and LBS was 265 seconds and 435 seconds respectively (p=0.012).  There was no difference in the treatment time duration in both groups. Keeping the clinical tolerance at 5 mm, a total of 96% of treatment sessions were within the tolerance in any direction (lateral, longitudinal or vertical) using SBS, compared to 89% for LBS (p=0.023). In translational directions, the difference in the two setup modalities was seen in the lateral direction (p<0.001) with no difference in the longitudinal and vertical directions. Similarly, there was a significant difference in the rotational error favouring SBS (p=0.031) over LBS. The median intrafraction movement was found to be 1.2 mm with SBS. 

Our study shows that the surface-based setup has definite advantage over the conventional laser-based setup in terms of setup time and positioning errors. The use of daily SGRT improves patient setup without additional imaging dose to breast cancer patients.