Evaluation of Setup Errors in Patients with Head and Neck Cancer Treated with IMRT Techniques using Electronic Portal Imaging Devices

Abstract

       The systematic and random setup errors for patients with head and neck cancer are specific
for each hospital. These values are essential for defining the clinical target volume (CTV) to
planning target volume (PTV) margin. Therefore, the objective of this study was to evaluate the
systematic and random setup errors for patients with head and neck cancer treated with intensity
modulated radiation therapy (IMRT) at Sakon Nakhon hospital and the appropriate CTV to PTV
margins were calculated. Thirty patients with head and neck cancer were enrolled from October,
2019 to September, 2020. The data of setup errors in 3 directions, longitudinal, lateral, and
vertical directions, were retrospectively collected from the Elekta Synergy Platform. The setup
errors between the 420 electronic portal imaging device (EPID) and digitally reconstructed
radiographs (DRRs) images were compared and calculated for the population systematic and
random setup errors. Then the CTV to PTV margins for three directions were calculated by
using the Van Herk equation.
        The results showed that the population systematic errors in longitudinal, lateral and vertical
directions were 0.43, 0.36 and 0.48 millimeter, respectively. The population random errors in
longitudinal, lateral and vertical directions were 1.08, 1.30 and 1.04 millimeter, respectively.
The determined CTV to PTV margins in longitudinal, lateral and vertical directions were 1.83,
1.80 and 1.92 millimeter, respectively. In conclusion, the CTV to PTV margins were less than
2.00 millimeter which were within the setup errors used for patients with head and neck cancer
at Sakon Nakhon hospital.
       Keywords: Setup error, Head and neck cancer, EPID, CTV to PTV margin