Adaptive MV portal imaging for head and neck cancer, a model for countries with limited resources

Background: Setup error had a considerable effect on treatment-related
uncertainty in head and neck cancer. Through this study, we examine adaptive
setup verification protocol using MV portal imaging in these patients.
Methods: A prospective phase 2 trial was conducted on 55 patients with
advanced head and neck cancer from 2018 till 2021. Patients received intensitymodulated radiotherapy using Varian© RapidArc. Online verification was done,
and setup error data were used to direct the frequencies of verification events.
One-year local failure representing geometrical miss and overall local control
were calculated. Patients’ setup accuracy data were collected, analysed and used
for calculation of the overall mean displacement (M), the population systematic
(∑), random (σ) errors and the van Herk formula (2.5 ∑ + 0.7 σ) for PTV
margin estimation. Local control where explored based on the frequency of
setup events.
Results: A total of 55 patients between 2018 and 2020, with 678 setup events
and 1356 Portal Vision verifications, were included in this study. Half of the
patients experienced reduced frequency of setup verifications, while 25.4%
required increased setup frequency. The 12-month RT field border failure rate
was 3.6%. The 12-month control rate of all patients was 74.5%; it was 69.2%,
76%, 76.9% for patients with increased, reduced and non-changed setup
frequency. The PTV margins were 3.5, 4.6, and 3.8 mm for vertical, lateral, and
longitudinal axes, respectively.
Conclusion: Despite the lack of CBCT imaging, adaptive megavoltage
PortalVision™ verification was effective in evaluation setup accuracy in head
and neck cancer patients.