ESTRO 2024 - Abstract Book

S5523

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2024

The daily CBCT images of 30 tattoo-less breast radiotherapy patients treated in 15 fractions, that were setup with SGRT for breast+ SIB or breast+ nodes at our departments were retrospectively re-matched to a breast-only match (n450). The accuracy of each match was recorded and analysed, and a F1-4&W imaging schedule was applied to assess the percentage of treatments that would have been delivered within tolerance (<0.5cm in all directions). The results were also compared with the setup accuracy of 100 past supine tangential breast-only radiotherapy patients that were positioned using a tattoo-alignment method to allow a comparison to existing practice. The tattooed patient cohort had electronic portal imaging (EPI) at the treatment angle on fractions 1-3 and weekly. The extra imaging fraction on fraction 4 for the tattoo-less setups was due to a new SGRT positioning reference being captured on fraction 1 after the CBCT shifts were applied, which required 3 subsequent fractions of imaging to verify setup consistency. In both cases, pre-treatment image verification was continued until 3 consecutive images were within tolerance, and then a move to weekly imaging was made. If a weekly image was out of tolerance, imaging was conducted for subsequent fractions until 2 consecutive images were within tolerance to ensure setup consistency. DIBH and free-breathing patients were included for both cohorts. Of the 450 tattoo-less SGRT setup fractions, 95.8% were simulated to be treated within tolerance. The magnitude of discrepancies from planned isocentre for the 4.2% of fractions simulated to be out of tolerance were 0.5cm (n= 5), 0.6cm (n= 9), and 0.7cm (n= 3). Therefore, the maximum discrepancy missed was 0.2cm outside of departmental breast protocol tolerance. The average discrepancies and standard deviations from isocentre for all tattoo-less fractions (n= 450) in each direction were Longitudinal: average= -0.01cm, SD=0.25cm, lateral: average= -0.02cm, SD= 0.21cm, and vertical: average= 0.04cm, SD= 0.23cm. When comparing the accuracy of the imaged fractions of the two setup techniques, tattoo-less SGRT setup patients had a 96% rate of images within tolerance while tattoo-alignment setup patient had 80% within tolerance. The overall imaging frequency rate for the tattoo-less cohort was 51% and 53% for the tattooed. Results:

Conclusion:

Tattoo-less SGRT provides a high level of setup accuracy for supine tangential breast-only radiotherapy with a F1-4&W CBCT imaging schedule, removes gross errors, and is sufficient to ensure patients are treated within tolerance for over 95% of fractions. It can be considered a reasonable alternative to daily imaging and moreover, this imaging protocol identifies and allows for an increase in imaging frequency as required to ensure treatment accuracy is maintained for patients whose positioning is inconsistent throughout their course of treatment.

Keywords: Tattoo-less setup, SGRT, Imaging frequency

References:

[1] Batista, V. et al Surface Guided Radiotherapy: An international survey on current clinical practise, Technical Innovations & Patient Support in Radiation Oncology (22), 2022.

[2] Moser T. et al Radiotherapy tattoos: Women’s skin as a carrier of personal memory- What do we cause by tattooing our patients?, The Breast Journal, 00:1-3, 2019.