Wang-Chia Ko¹, Yulin Song²*, Hao-Yun Hsu², Boris A. Mueller³, David Guttmann³, Luke Pike³, Paul Tamas³, Miao Zhang², Josh Yamada³, (1) Department of Biostatistics, MSPH, Columbia University, NY, USA (2) Department of Medical Physics, Memorial Sloan Kettering Cancer Center, NY, USA (3) Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, NY, USA

PO-GePV-M-247 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: Permanent skin tattoos have been part of standard care for paraspinal patients undergoing EBRT. In this study, we prospectively evaluated tattooless setup with 3D surface imaging and compared it with the skin tattoo-based approach.

Methods: Patients receiving paraspinal radiation therapy underwent a standard tattoo-based setup, alternating daily with a tattooless setup by surface imaging. Following the initial setup, the patient position was verified by daily CBCT imaging, with matching on the bone or surgical hardware to represent ground truth. Translational and rotational shifts determined by CBCT imaging were recorded, as were setup time duration and total in-room time duration. Statistical analysis was performed using the non-parametric Wilcoxon Rank-Sum test and F-test for Equality of Two Variances.

Results: We evaluated 57 individual treatments from 14 paraspinal patients, 22 treated under surface imaging, and 35 under a traditional tattoo-based setup. The distributions of entire in-room time duration and set up time duration are right-skewed in both cohorts and are not normally distributed. The median entire in-room time duration and set up time duration in the surface imaging cohort are indifferent from those of the traditional skin tattoo cohort (p = 0.417 and 0.597, respectively). The variance of position shift in LNG direction in the 3D surface imaging cohort is significantly different from that of the traditional skin tattoo cohort (p = 0.0069). There is insufficient evidence (p > 0.05) to indicate a difference in variance or mean between the two cohorts in other directions.

Conclusion: Our preliminary results suggest that a tattooless setup approach to paraspinal radiotherapy with surface imaging may be sufficiently accurate for initial patient setup. Further analyses among large cohorts and including delivered dosimetry will determine whether standard tattoo-based approaches can be replaced by 3D surface imaging.

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