Introduction: Rectal cancer is among the most common forms of cancer. Due to anatomical
characteristics and the proximity of critical organs, precise patient positioning during
irradiation is essential. The use of advanced technologies, such as surface-guided
radiotherapy, helps minimise the need for repeated patient repositioning into the correct
treatment position. Purpose: The aim of this master’s thesis was to evaluate the impact of
surface-guided radiotherapy systems on the accuracy of translational shifts in patients with
rectal cancer and on the number of additional cone-beam computed tomography verifications
during irradiation of patients with the Varian TrueBeam and Varian Halcyon linear
accelerators. The objective was to determine whether the use of these systems reduces
patient movement and consequently improves the overall quality of radiotherapy treatment.
Methods: A retrospective study with a descriptive research method was conducted. Data
from 100 patients with rectal cancer, irradiated at the Institute of Oncology Ljubljana
between April 2019 and April 2025, were analysed. The magnitude of translational shifts in
the lateral, longitudinal, and vertical directions was compared. Additionally, the number of
additional cone-beam computed tomography verifications was compared between 50
patients treated with surface-guided radiotherapy on the Varian TrueBeam linear accelerator
and 50 patients treated on the Varian Halcyon linear accelerator without these systems.
Results: The results showed that translational shifts in patients treated on the TrueBeam
linear accelerator with surface-guided radiotherapy were smaller in all directions compared
with patients treated on the Halcyon linear accelerator. In addition, fewer additional cone
beam computed tomography verifications were required in the TrueBeam group, indicating
more accurate patient positioning during radiotherapy. Discussion and Conclusion: The
findings confirm that surface-guided radiotherapy systems significantly improve the patient
positioning process prior to irradiation. The use of surface-guided radiotherapy systems is
therefore also recommended for Varian Halcyon linear accelerators, as this would further
enhance the quality of radiotherapy procedures in patients with rectal cancer.
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