Clinical Validation of two Surface Imaging Systems for Patient   Positioning in Percutaneous Radiotherapy
  Precise patient positioning and thus precise positioning of the planning target volume (PTV) is a prerequisite for effective treatment in percutaneous radiation therapy. Conventional imaging modalities used to ensure exact positioning for treatment typically involve additional radiation exposure of the patient. A different approach to patient alignment without additional exposure is provided by optical 3D surface scanning and registration systems.   We investigated two systems Catalyst and AlignRT, which allowed us to generate and validate surface images of 50 patients undergoing irradiation on a Tomotherapy system. We compared the positions proposed by these two surface imaging systems (SIS) with the actual adjustments in patient positions made on the basis of MVCT scans. With the two SIS, the surface of every single patient was repeatedly recorded throughout treatment. In addition, we performed a systematic analysis of both systems using a body phantom.   At least 10 surface images were available from each patient included in the analysis. The large number of patients allowed us to subdivide the study population into three groups by body region treated: head & neck, chest, and pelvic. The results for each of these three body regions were separately analyzed. Thus, the focus of our investigation is on body regions registered with the two systems rather than tumor entities. For AlignRT, for instance, we found an improvement in positioning for the Pelvic region of 0.9mm in 75% and 6.4mm in 95% of the collected data in comparison to conventional marker alignment.   The two systems were most accurate in the head & neck region, where conventional mask alignment is already sufficiently accurate. The other two body regions, pelvic and chest, might benefit from positioning by SIS. But for both systems there is still a need for improvement to reduce statistical variation. 
Manfred Wiencierz, Kathrin Kruppa, and Lutz L\"udemann
physics.med-ph