title: Comparison between infrared optical and stereoscopic X-ray technologies for patient setup in image guided stereotactic radiotherapy.
abstract: OBJECTIVE
  To compare infrared (IR) optical vs. stereoscopic X-ray technologies for patient setup in image-guided stereotactic radiotherapy.
  
  
  METHODS
  Retrospective data analysis of 233 fractions in 127 patients treated with hypofractionated stereotactic radiotherapy was performed. Patient setup at the linear accelerator was carried out by means of combined IR optical localization and stereoscopic X-ray image fusion in 6 degrees of freedom (6D). Data were analyzed to evaluate the geometric and dosimetric discrepancy between the two patient setup strategies.
  
  
  RESULTS
  Differences between IR optical localization and 6D X-ray image fusion parameters were on average within the expected localization accuracy, as limited by CT image resolution (3 mm). A disagreement between the two systems below 1 mm in all directions was measured in patients treated for cranial tumors. In extracranial sites, larger discrepancies and higher variability were observed as a function of the initial patient alignment. The compensation of IR-detected rotational errors resulted in a significantly improved agreement with 6D X-ray image fusion. On the basis of the bony anatomy registrations, the measured differences were found not to be sensitive to patient breathing. The related dosimetric analysis showed that IR-based patient setup caused limited variations in three cases, with 7% maximum dose reduction in the clinical target volume and no dose increase in organs at risk.
  
  
  CONCLUSIONS
  In conclusion, patient setup driven by IR external surrogates localization in 6D featured comparable accuracy with respect to procedures based on stereoscopic X-ray imaging.
authors: Division of Radiation Oncology, European Institute of Oncology, Milano, Italy. tagaste@cnao.it
authors: Barbara
authors: B
authors: Tagaste
authors: Marco
authors: M
authors: Riboldi
authors: Maria F
authors: MF
authors: Spadea
authors: Simone
authors: S
authors: Bellante
authors: Guido
authors: G
authors: Baroni
authors: Raffaella
authors: R
authors: Cambria
authors: Cristina
authors: C
authors: Garibaldi
authors: Mario
authors: M
authors: Ciocca
authors: Gianpiero
authors: G
authors: Catalano
authors: Daniela
authors: D
authors: Alterio
authors: Roberto
authors: R
authors: Orecchia