Room: Exhibit Hall | Forum 6
Purpose: Chest patients have traditionally been set-up with tattoos and lasers. This process is subject to error (incorrect tattoo placement, incorrect tattoo identification) and causes discomfort to the patient. An alternative to tattoos is to set-up the patient using surface imaging.
Methods: Ten chest patients were initially positioned with tattoos and lasers, then underwent a cone beam computed tomography (CBCT) scan that was registered based on bony anatomy. Ten different chest patients were initially positioned with AlignRT (VisionRT, London, UK) then with CBCT as described above. The translations determined by the CBCT registration were recorded for each group.
Results: The tattoo group had 6 females and 4 males, the mean number of fractions was 30 +/- 3 (26-34) [+/- 1 SD (range)]. The AlignRT group had 4 females and 6 males with mean fractions 21 +/-10 (10-33). The mean magnitude of the lateral, longitudinal, and vertical shifts for the tattoo group were 2.5 cm+/- 2.5 cm (0-7.2 cm), 0.7 cm +/- 0.6 cm (0-5.2 cm), and 0.3 cm +/- 0.2 cm (0-1.4 cm) over 302 fractions, respectively. The mean lateral, longitudinal, and vertical shifts for the AlignRT group were 2.7 cm +/- 2.2 cm (0-7.2 cm), 0.5 cm +/- 0.4 cm (0-1.7 cm), and 0.4 cm +/- 0.3 cm (0-1.8 cm) over 209 fractions, respectively.
Conclusion: In some cases the day to day lateral variations were large due to intentional pre-CBCT shifts for clearance. In all dimensions the mean shifts and variance for the AlignRT group were comparable to the tattoo group. Based on this data, surface imaging offers equivalent set-up accuracy to tattoos for chest patients, and it may be reasonable to replace tattoo based set-ups with surface imaging.