Optical surface mapping to complement use of CBCT in SBRT of lungs

Full text: SBRT is our standard treatment for early stage inoperable NSCLC. High fractional dose necessitates positional verification before and during treatment. Elekta Synergy CBCT is used to assess correct isocentre position relative to the target. AlignRT (Vision RT, UK) is a real-time patient surface mapping system using optical technology. Its potential is evaluated for complementing CBCT and for predicting when additional CBCT scans may be required, to improve SBRT delivery safety but also to reduce treatment times. From initial patient CBCT scans, translational couch movements are applied to ensure all visible tumour is within an ITV. Further CBCT scans immediately before and after treatment verify position pre-treatment start and assess intra-treatment tumour positional changes, respectively. CCTV monitoring is also used in treatment, with additional CBCTs if significant patient movement i: observed. AlignRT was used in gated mode to generate patient sur faces at maximum expiration, after the scans immediately before and after treatment delivery. Intra-treatment patient position shifts calculated from surface matching from Align-RT, using whole chest abdomen and sternum ROIs, were compared to those from CBCT. Results and Conclusions 19 patients were monitored in an initial feasibility study. Whole chest and sternum ROI matching was mos consistent with CBCT, with 95% of shifts from Align-RT within 1.5-2 mm of those from CBCT, laterally and vertically; 3 mm Iongitudinally. More data are needed, particularly from patients demonstrating significant movements during treatment, to conclusively evaluate the system, but from this work combining optical mapping with CBCT appears a feasible approach.