Validation of a weekly imaging protocol for tangential whole breast radiation therapy with a tattoo-less surface-guided setup

This study explored whether tattoo-less surface guided setups with a first 4 fractions then weekly imaging schedule (F1-4&W) is a suitable alternative to tattoo alignment setups for adjuvant whole breast radiotherapy (WBRT) patients. The daily CBCT images (n = 450) of 30 patients treated using tattoo-less surface-guided radiation therapy (SGRT) were retrospectively re-matched to a WBRT protocol. The accuracy of the re-match was assessed, and a F1-4&W imaging schedule applied to investigate the percentage of fractions that would have been treated to a 0.5 cm tolerance. The results were compared with the setup accuracy of 100 consecutive patients treated with WBRT using the existing practice of tattoo-based alignment. 95.8 % of the tattoo-less SGRT setup fractions were assessed to be treated within tolerance, with a maximum discrepancy from isocentre of 0.7 cm for a non-imaged fraction. When comparing imaged fractions, 98 % of these patients positioned within 0.5 cm of isocentre, while the tattoo-alignment method achieved this only 80 % of the time. The overall imaging frequency rates per patient were 51 % and 53 % for study (SGRT/CBCT) and control groups (EPI/tattoos) respectively. We conclude that tattoo-less SGRT provides a consistently accurate method to setup supine tangential WBRT patients with a benefit to patient experience. Furthermore, a F1-4&W imaging schedule is sufficient to ensure patients are treated within tolerance, while maintaining appropriate indication for when increased imaging frequency is necessary.