Abstract PS15-02: Permanent marker free surface-guided breast radiotherapy: Implementing a new technique

Background:It is standard practice in our centre for patients to be given permanent skin marks during breast radiotherapy planning, for use as reliable landmarks in daily reproduction of their positioning for treatment. However, these permanent marks (tattoos) may have a significant psychological impact on patients (1). In recent years, there have been technological advances in surface-guided radiotherapy techniques (SGRT) which may provide improved set-up accuracy compared to permanent markers.Aims:1. To evaluate if surface-guided set-up is as good, if not better, than set-up with permanent markers alone.2. To safely implement a permanent marker (PM) free, surface-guided set-up technique.Methods:A pilot study was conducted with tangents-only breast patients treated in free breathing (FB). All treatments were delivered on Varian TrueBeam linear accelerators, with patients immobilised on a couch indexed breast board. The study group (n=20) were set up using PMs with adjustments guided by the AlignRT® SGRT system to optimise patient positioning. Imaging (MV tangent images) was performed as per standard protocol on fractions 1-3, 8 and 12. Additional imaging was performed if indicated. The translational and rotational displacements calculated by the TrueBeam verification system for this group were compared to average displacements calculated for patients set up using PMs alone (the control group, n=20). Encouraged by the results of the pilot study, the centre moved to safely roll-out the PM-free technique to include additional applications. The step-wise approach taken will be described.Results:The mean displacements calculated from the verification imaging are shown in Table 1 below: SGRT set-up demonstrated statistically-significant improvements compared to PM set-up alone with respect to lateral, vertical and total translational displacements. Longitudinal displacements favoured PM set-up alone but this did not reach statistical significance. Rotational displacements favoured SGRT set-up and the results reached statistical significance.Given the improved set-up accuracy with SGRT, and the wish to reduce the psychological morbidity of radiotherapy for our breast cancer patients, the centre moved to safely implement a PM free SGRT technique along agreed timelines as shown in Table 2: Conclusions:Our pilot study demonstrated that surface-guided radiotherapy (SGRT) set-up is as good, if not better, than set-up with permanent markers (PM) alone in tangent-only free-breathing patients. Subsequent further analysis showed improved consistency of set-up guided by PM plus SGRT for all breast set-ups (to include nodal regions and DIBH). We have described our step-wise approach to setting up PM free radiotherapy delivery for breast cancer patients, which has additional advantages in maintaining social distancing in the COVID19 era.Refs1. Psychosocial impacts of radiation tattooing for breast cancer: a critical review. B Clow et al. Citation Format: Christy Goldsmith, Deirdre Dobson, Adam Littler, Elinor Sawyer, Georgina Moriggi, Roshni Chauhan. Permanent marker free surface-guided breast radiotherapy: Implementing a new technique [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS15-02.