The Catalyst HD (C‐RAD Positioning AB, Uppsala, Sweden) optical surface imaging (OSI) system is able to manage interfractional patient positioning, intrafractional motion monitoring, and non‐contact respiratory gating without x‐ray exposure for radiation therapy. In recent years, a novel high‐precision surface registration algorithm for stereotactic radiosurgery (SRS algorithm) has been released. This study aimed to evaluate the technical performance of the OSI system using rigid phantoms, by comparing the conventional and SRS algorithms. To determine the system’s technical performance, isocenter displacements were calculated by surface image registration via the OSI system using head, thorax, and pelvis rigid phantoms. The reproducibility of positioning was evaluated by the mean value calculated by repeating the registration 10 times, without moving each phantom. The accuracy of positioning was evaluated by the mean value of the residual error, where the 10 offset values given to each phantom were subtracted from the isocenter displacement values. The stability of motion monitoring was evaluated by measuring isocenter drift during 20 min and averaging it over 10 measurements. For the head phantom, all tests were compared with the mask types and algorithms. As a result, for all sites and both algorithms, the reproducibility, accuracy, and stability for translation and rotation were <0.1 mm and <0.1°, <1.0 mm and <1.0°, and <0.1 mm and <0.1°, respectively. In particular, the SRS algorithm had a small absolute error and standard deviation of calculated isocenter displacement, and a significantly higher reproducibility and accuracy than the conventional algorithm (P < 0.01). There was no difference in the stability between the algorithms (P = 0.0280). The SRS algorithm was found to be suitable for the treatment of rigid body sites with less deformation and small area, such as the head and face.
PurposeTo investigate the effect of an integral quality monitor (IQM; iRT Systems GmbH, Koblenz, Germany) on 4, 6, 10, and 6‐MV flattening filter‐free (FFF) photon beams.MethodsWe assessed surface dose, PDD20,10, TPR20,10, PDD curves, inline and crossline profiles, transmission factor, and output factor with and without the IQM. PDD, transmission factor, and output factor were measured for square fields of 3, 5, 10, 15, 20, 25, and 30 cm and profiles were performed for square fields of 3, 5, 10, 20, and 30 cm at 5‐, 10‐, and 30‐cm depth.ResultsThe differences in surface dose of all energies for square fields of 3, 5, 10, 15, 20, and 25 cm were within 3.7% whereas for a square field of 30 cm, they were 4.6%, 6.8%, 6.7%, and 8.7% for 4‐MV, 6‐MV, 6‐MV‐FFF, and 10‐MV, respectively. Differences in PDD20,10, TPR20,10, PDD, profiles, and output factors were within ±1%. Local and global gamma values (2%/2 mm) were below 1 for PDD beyond dmax and inline/crossline profiles in the central beam region, respectively. The gamma passing rates (10% threshold) for PDD curves and profiles were above 95% at 2%/2 mm. The transmission factors for 4‐MV, 6‐MV, 6‐MV‐FFF, and 10‐MV for field sizes from 3 × 3 to 30 × 30 cm2 were 0.926–0.933, 0.937–0.941, 0.937–0.939, and 0.949–0.953, respectively.ConclusionsThe influence of the IQM on the beam quality (in particular 4‐MV X‐ray has not verified before) was tested and introduced a slight beam perturbation at the surface and build‐up region and the edge of the crossline/inline profiles. To use IQM in pre‐ and intra‐treatment quality assurance, a tray factor should be put into treatment planning systems for the dose calculation for the 4‐, 6‐, 10‐, and 6‐MV flattening filter‐free photon beams to compensate the beam attenuation of the IQM detector.
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