Background Laser scanning-based patient surface positioning and surveillance may complement image-guided radiotherapy (IGRT) as a nonradiation-based approach. We investigated the performance of an optical system compared to standard kilovoltage cone-beam computed tomography (CBCT) and its potential to reduce the number of daily CBCTs. Patients and methods We analyzed the patient positioning of 153 treatment fractions in 21 patients applied to three different treatment regions. Patients were first scanned with CBCT, shifted to the optimal isocenter position, and an optical scan was performed to verify the matching in relation to CBCT. Results For the head-and-neck region, the lateral/longitudinal/vertical/rotational/roll and pitch shift was 0.9 ± 1.8 mm/−2.7± 3.8 mm/−0.8± 3.6 mm/0.0± 1.1°/−0.5± 2.1°/0.2± 1.6°. For the thorax, the lateral/longitudinal/vertical/roll and pitch shift was −1.2± 3.6 mm/0.8± 5.1 mm/0.8± 4.3 mm/0.6± 1.4°/0.1± 0.9°/0.3± 1.0°. For the pelvis, the respective values were −2.5± 4.1 mm/4.6± 7.3 mm/−5.1± 7.4 mm/0.3± 1.1°/-0.5± 1.0°/0.3± 2.1°. In total, the recorded disagreement was −1.0± 3.6 mm/1.0± 6.3 mm/−1.8± 5.9 mm/0.3± 1.2°/−0.3± 1.5°/0.2± 1.7°. Conclusion This analysis showed good agreement between the optical scanner approach and CBCT. The optical system holds potential to ensure precise patient positioning and reduced CBCT frequency in tumor locations with fixed relation to surface structures.