182. Study of the accuracy of non-invasive fixation frames in brain treatments with Helical Tomotherapy

Abstract

PurposeThe study focused on the accuracy of intracranial frame-less radiosurgery (RS) and intracranial hypo-fractionated treatments (HFT), delivered with helical Tomotherapy (HT), by means of two different mask-based fixation systems (FPM = Five Point Mask and DSPS = Double Shell Positioning System). MethodsA Megavoltage Computed Tomography (MVCT) was acquired and automatically registered with the planning CT of a Rando phantom, to evaluate the delivery accuracy of the HT image guided positioning tool. After the application of the suggested shifts, the phantom was scanned a second time and shifts in each direction and rotations were recorded; the vector displacement (v) was calculated as the square sum of the shifts in each directions. Analogous procedure was applied to 14 and 16 patients underwent intracranial HFT and RS respectively: overall 59 MVCT performed at the end of the treatment were acquired and analyzed. The v were analyzed in order to evaluate the intra-fraction motions. ResultsThe mean v, obtained in the phantom acquisitions, was 0.4 ± 0.2 mm, showing that HT-IGRT system is able to achieve positioning accuracy typical of RS (v<1mm). Moreover, the mean rotational variations were negligible. Results on the patient treatments, reported in Table 1, showed that both masks minimized the intra-fraction motion to an extent of 1 mm (with no statistically difference between FPM and DSPS: p < 0.573, Mann-Whitney Test). No dependence of v on the treatment time was observed. ConclusionsOur study demonstrates that mask-based fixation systems have a high intracranial positioning accuracy, comparable with for invasive immobilization systems (v = 0.6 ± 0.9 mm (range: 0.3–1.7 mm) [1]), therefore, they could be used for high-precision treatments, like RS. [Display omitted]