3D optoelectronic analysis of interfractional patient setup variability in frameless extracranial stereotactic radiotherapy.
OBJECTIVE
To investigate size and frequency of interfractional patient setup variability in hypofractionated stereotactic extracranial radiotherapy.


METHODS
Infrared optical 3D tracking of surface markers was applied to quantify setup variability on 51 patients. Isocenter position repeatability was assessed by means of frameless anatomic calibration and was compared with portal image evaluation. Specific data analysis allowed for compensation of patients' breathing movements and for separation of the effects of operator-dependent misalignments and respiration-induced displacements. Effects of patient position (supine vs. prone) and treatment table configuration were investigated.


RESULTS
Patient positioning assisted by the optical tracking device allowed reducing displacements of surface control points within the 3-mm range. Errors in isocenter localization were in the range of a few millimeters. This was in agreement with the portal image evaluation. Breathing motion introduced appreciable errors, which increased control points and isocenter 3D variability. This effect was significantly higher than those related to other investigated factors.


CONCLUSIONS
The role of infrared optical tracking devices for patient positioning is assessed on a large patient population. Their use in the frame of high-precision radiotherapy is emphasized by the application of related methodologies for breathing phase detection and frameless isocenter localization.
Baroni
Guido
G
Department of Bioengineering, Politecnico di Milano University, Milan, Italy. guido.baroni@polimi.it
Garibaldi
Cristina
C
Riboldi
Marco
M
Spadea
Maria F
MF
Catalano
Gianpiero
G
Tagaste
Barbara
B
Tosi
Giampiero
G
Orecchia
Roberto
R
Pedotti
Antonio
A
D000008:Abdominal Neoplasms / Q000532:radiotherapy*; D002138:Calibration; D019583:Dose Fractionation, Radiation; D006801:Humans; D007259:Infrared Rays; D010386:Pelvic Neoplasms / Q000532:radiotherapy*; D016684:Prone Position; D015203:Reproducibility of Results; D012119:Respiration; D013238:Stereotaxic Techniques; D016683:Supine Position; D013899:Thoracic Neoplasms / Q000532:radiotherapy*