Quality assurance of four-dimensional computed tomography in a multicentre trial of stereotactic body radiotherapy of centrally located lung tumours

Abstract

Background and Purpose: Extensive radiation therapy quality assurance (RTQA) programs are needed when advanced radiotherapy treatments are used. As part of the RTQA four dimensional computed tomography (4DCT) imaging performance needs to be assessed. Here we present the RTQA data related to 4DCT procedures used within the context of stereotactic body radiotherapy (SBRT) of centrally located lung tumours. It provides an overview of the 4DCT acquisition methods and achievable accuracy of imaging lung tumour volumes. Materials and Methods: 3DCT and 4DCT images were acquired from a CIRS phantom with spheres of 7.5 and 12.5 mm radius using the institutional scan protocols. Regular asymmetric tumour motion was simulated with varying amplitudes and periods. Target volumes were reconstructed using auto-contouring with scanner specific thresholds. Volume and amplitudes deviations were assessed. Results: Although acquisition parameters were rather homogeneous over the eleven institutions analysed, volume deviations were observed. Average volume deviations for the 12.5 mm sphere were 15% (−4% to 69%) at end of inspiration, 2% (−2% to 9.0%) at end of expiration and 12% (0% to 36%) at mid-ventilation. For the 7.5 mm sphere deviations were 13% (−99% to 65%), 16% (−34% to 66%) and 1% (−13% to 20%), respectively. The amplitude deviation was generally within 2 mm although underestimations up to 6 mm were observed. Conclusions: The expiration phase was the most accurate phase to define the tumour volume and should be preferred for GTV delineation of tumours exhibiting large motion causing motion artefacts when using midventilation or tracking techniques. The large variation found among the institutions indicated that further improvements in 4DCT imaging were possible. Recommendations for 4DCT QA have been formulated.

Experimental validation of 4D log file‐based proton dose reconstruction for interplay assessment considering amplitude‐sorted 4DCTs

“…In this study, we used 12 phases in the 4DCT phase reconstruction as opposed to the commonly clinically used 8–10 phases 21,43 . We decided for a higher than usual number of phases for two reasons: the higher number of non‐overlapping reconstructed phases leads to a better sampling of the motion curve data and therefore to smaller geometrical differences between adjacent 4DCT phases.…”

Independent review of 4DCT scans used for SABR treatment planning

“…Recently the European Organisation for Research and Treatment of Cancer (EORTC) multicentre Lungtech trial reported on the results of RTQA activities for 4DCT across 11 centers. Large deviations in contour volume of up to 99% were found across different sites despite imaging the same phantom under the same motion pattern . The effects of irregular breathing patterns on ITV delineation of moving targets in the context of lung SABR have been described by Clements et al who demonstrated erroneous ITV delineation using MIP images for moving targets with large amplitude undergoing irregular motion patterns.…”

“…Large deviations in contour volume of up to 99% were found across different sites despite imaging the same phantom under the same motion pattern. 12 The effects of irregular breathing patterns on ITV delineation of moving targets in the context of lung SABR have been described by Clements et al 13 who demonstrated erroneous ITV delineation using MIP images for moving targets with large amplitude undergoing irregular motion patterns. Similar findings have been reported by Park et al 14…”

Imaging science and development in modern high-precision radiotherapy

“…Consequently, dual energy CT (DECT) was proposed as an alternative CT-technique for proton therapy planning [28] , [29] , [30] , [31] , [32] , [33] , [34] . Furthermore, time-resolved CT imaging, so-called 4D-CT, has been shown to inform about tumor and organ motion and thus provide valuable information to be integrated into RT planning and delivery [24] , [35] , [36] .…”