Permanent marker free surface-guidedbreast radiotherapy: Implementing a new technique

Background: It is standard practice in our centre for patients to be given permanent skin marks during breastradiotherapy 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, therehave been technological advances in surface-guided radiotherapy techniques (SGRT) which may provide improvedset-up accuracy compared to permanent markers Aims: 1 To evaluate if surface-guided set-up is as good, if notbetter, 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 freebreathing (FB) All treatments were delivered on Varian TrueBeam linear accelerators, with patients immobilised ona couch indexed breast board The study group (n=20) were set up using PMs with adjustments guided by theAlignRT SGRT system to optimise patient positioning Imaging (MV tangent images) was performed as perstandard protocol on fractions 1-3, 8 and 12 Additional imaging was performed if indicated The translational androtational displacements calculated by the TrueBeam verification system for this group were compared to averagedisplacements calculated for patients set up using PMs alone (the control group, n=20) Encouraged by the resultsof the pilot study, the centre moved to safely roll-out the PM-free technique to include additional applications Thestep-wise approach taken will be described Results: The mean displacements calculated from the verificationimaging are shown in Table 1 below: SGRT set-up demonstrated statistically-significant improvements compared to PM set-up alone with respect tolateral, vertical and total translational displacements Longitudinal displacements favoured PM set-up alone but thisdid not reach statistical significance Rotational displacements favoured SGRT set-up and the results reachedstatistical significance Given the improved set-up accuracy with SGRT, and the wish to reduce the psychologicalmorbidity of radiotherapy for our breast cancer patients, the centre moved to safely implement a PM free SGRTtechnique 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 analysisshowed improved consistency of set-up guided by PM plus SGRT for all breast set-ups (to include nodal regionsand DIBH) We have described our step-wise approach to setting up PM free radiotherapy delivery for breast cancerpatients, which has additional advantages in maintaining social distancing in the COVID19 era