I. INTRODUCTION
For 3D conformal and intensity modulated radiation therapy
techniques, patient repositioning is a critical issue in everyday
practice. Patient setup is performed by aligning room
localization lasers to tattoos marked on patients’ skin and
verified using portal images or cone beam computed tomography
(CBCT). Both of these techniques have improved the
accuracy of radiation delivery and are, nowadays, indispensable
tools for patient positioning and target localization verification.
Both CBCT and portal imaging carry a radiation
dose that must be clinically evaluated and on a case-by-case
basis, before deciding its daily use; several studies have in
fact been performed so as to measure the additional exposure
deriving from the verification procedure and optimize the
imaging acquisition protocol.1–3
An alternative approach consists in comparing a 3D model
of the patient’s external surface with the data acquired with an
optical system when the patient is on the treatment couch.
In this case, the system uses only a target surrogate (the
patient’s skin) instead of a more complete internal anatomy,
but the main advantage of such an approach is the absence
of additional radiation exposure.
Two commercial systems have been presented in the last
few years: AlignRT (VisionRT, London, United Kingdom),
using speckle projection photogrammetry approaches and,
later on, Sentinel
TM
, a laser camera system proposed by
C-RAD (Uppsala Sweden).
While several studies4–7 over the last 5 years were performed
on AlignRT to evaluate its applicability and technical
performance, little data have been presented on Sentinel8,9 or
similar apparatus.10