The accuracy of the Sentinel surface scanning system regarding stability and
reliability was shown earlier by Palotta et. al.. The group compared the performance
of Sentinel to CBCT and portal imaging based on rigid phantoms. They explicitly
mentioned, however, that their results were not meant to be an indication of the
clinical accuracy [4]. The clinical study of Moser et. al. analysed the Galaxy scanning
system (LAP Laser, Lüneburg, Germany) on a TomoTherapy unit (Tomotherapy,
Madison, WI) with megavoltage computed tomography (MVCT) based on 20 patients
and 200 fractions. Similar to our study, they compared the deviations between the
reference surface and the MVCT and found larger systematic shifts within 3-9 mm
which were explained with incomplete surface scans due to the single camera
system and breathing motion. In addition, they compared the deviation between a
optical reference scan and daily optical scans and they found no clinically relevant
shifts [9]. Gopan et. al. studied another surface scanning system (AlignRT) but mainly
focussing on head-and-neck targets. Our results for this scanning region are similar
to theirs (rotation 0.8°-2.2° and translation 2.4mm-4.5mm) with somewhat better
agreement in our series that very likely has a different population and fixation system
to start with. They found a larger discrepancy (rotation 1.9°-4.5° and translation
6.9mm-11.9mm) for non-rigid registration of head-and-neck targets which can not be
compared to our study due to a non-rigid registration algorithm not being available for
Sentinel at the time of the analysis [5]. The group of Kauweloa et. al. used their
surface tracking system (GateCT) for respiratory signal reconstruction in 4DCT
imaging based on phantom measurement. Their results are hardly comparable to our
study but they could show that their system provided consistent temporal/phase
tracking [6]. Placht et. al. developed a novel preregistration algorithm in conjunction
with a time of flight (ToF) camera. Based on unspecified phantom measurements,
they found a mean registration error for translations of 1.6±1.0 mm and for rotations
0.07±0.05° similar to our clinical results [7]. Our results show good agreements of the
surface scanning method for patient positioning.