Tese de mestrado integrado, Engenharia Biomédica e Biofísica (Radiações em Diagnóstico e Terapia), 2022Stereotactic Radiosurgery (SRS) has been consolidated in recent years as the treatment of
choice in selected central nervous system (CNS) tumors. With the introduction of stereotactic
approach in clinical practice, accurate immobilization and motion control during treatment becomes
fundamental. During SRS treatments, the common practice is to immobilize CNS patients in a cushion
molded head support, with specific open-face thermoplastic masks. To verify and correct internal
isocenter uncertainties before and during treatment, X-Ray volumetric imaging (XVI) is performed -
image guided radiation therapy (IGRT).
An alternative to mid‐treatment imaging is optical surface detection (OSD) imaging – a
non‐invasive, non‐radiographic form of image guidance – to monitor patient intra-fraction motion.
This imaging technique has shown to properly position, accurately monitor, and quantify patient
movements throughout the entirety of the treatment – surface guided radiation therapy (SGRT).
The aim of this investigation is to test the viability of the implementation of a maskless
immobilization approach, using only a vacuum mouthpiece suction system for head fixation in patients
with CNS tumors who will undergo SRS treatment under the guidance of an OSD system coupled with
6-Degree of Freedom (6-DOF) robotic couch for submillimeter position correction. This master thesis
addresses the five technical performance tests conducted on the Linear Accelerator components –
XVI, HexaPOD couch and OSD system in the Radiotherapy Department of Hospital CUF
Descobertas.
The results obtained lecture the best acquisition orientation to perform image verification; if
the HexaPOD couch is correctly calibrated to the XVI radiation isocenter to assure submillimeter
corrections; OSD system performance regarding phantom surface detection since some immobilization
components can block the signal reading; which coplanar and non-coplanar angles occur most signal
inconsistencies due to camera pod occlusion; what is the overall OSD system accuracy and what is the
best non-coplanar angle arrangement to perform an SRS treatment with OSD system monitoring
