Distributive quality assurance and delivery of stereotactic ablative radiotherapy treatments amongst beam matched linear accelerators: A feasibility study.

PURPOSE: Beam matching occurs on all linacs to some degree and when two are more are matched to each other, patients are able to be transferred between machines. Quality assurance of plans can also be performed "distributively" on any of the matched linacs. The degree to which machines are matched and how this translates to like delivery of plans has been the focus of a number of studies. This concept has not yet been explored for stereotactic techniques which require a higher degree of accuracy. This study proposes beam matching criteria which allows for the distributive delivery and quality assurance of stereotactic body radiotherapy (SBRT) plans. METHOD: Two clinically relevant and complex volumetric modulated arc therapy (VMAT) SBRT spine and lung plans were chosen as benchmarking cases. These were delivered on nine previously beam matched linacs with quality assurance performed through ArcCheck and film exposure in the sagittal plane. Measured doses were compared to their treatment planning system predictions through gamma analysis at a range of criteria. RESULTS: Despite differences in beam match parameters and variations in small fields, all nine linacs produced accurate deliveries with a tight deviation in the population sample. Pass rates were well above suggested tolerances at the recommended gamma criterion. Film was able to detect dose errors to a greater degree than ArcCheck. CONCLUSION: Distributive quality assurance and delivery of stereotactic ablative radiotherapy treatments amongst beam matched linacs is certainly feasible provided the linacs are matched to a strict protocol like that suggested in this study and regular quality assurance is performed on the matched fleet. Distributive quality assurance and delivery of SBRT provides the possibility of efficiency gains for physicists as well as treatment staff.

Endoscopic assessment of free flap perfusion in the upper aerodigestive tract using indocyanine green: a pilot study.

INTRODUCTION: Malfunction of microvascular anastomoses is the main reason for free-flap failures. The aim of this investigation was to prove the feasibility of endoscopic free-flap perfusion measurements in the upper aerodigestive tract (UADT) using indocyanine green (ICG). METHODS: Twenty-five patients undergoing free-flap reconstruction of the UADT were included. At least three ICG angiographies (0 h, 24 h and 72 h) were performed per participant. The sequences were subjectively judged online. The data were subsequently analysed, the results compared to clinical outcome and a survey with clinical staff (n = 21) performed. RESULTS: All 25 flaps survived. The ICG angiographies were tolerated well, showing a delayed fluorescence gain in transplanted tissue compared to surrounding but comparable final maximum fluorescence intensities. Four surgical revisions (two for a true and two for a false indication) could be additionally investigated. The two flaps with a real perfusion compromise showed fluorescence Indices (relative fluorescence maxima of transplant vs. surrounding) of 33% and 37%, whereas these values lay above 60% for all other examinations (including those two flaps that were revised for a false indication). The survey showed that ICG angiography leads to a better discrimination of well- and malperfused flaps compared with conventional inspection. CONCLUSION: In this small level IIb study, it was possible to prove the feasibility of endoscopic ICG angiography in patients with free-tissue transfer to the UADT. In difficult situations, it seems a welcome adjunct to conventional screening and might aid in the decision whether to revise a clinically suspect flap.