Clinical Evaluation of Tattoo-less SGRT-aided Breast RT Program
Published:
Background
In preparation for adjuvant breast radiation therapy (RT), permanent skin tattoo marks are often placed on patient’s skin to assist patient’s positioning on treatment couch. However, those marks are often undesirable, in particular, for breast patients due to various drawbacks. With advancements in surface-guided radiation therapy (SGRT), it becomes possible to set up a patient through a “tattoo-less” approach and this study evaluates the efficacy and dosimetric implications of this tattoo-less setup technique.
Methods
A retrospective analysis of 30 patients diagnosed with right-sided breast cancer was included in this study. All the patients received an initial whole breast dose of 42.56 Gray (Gy) in 16 daily fractions using a tangential 3D conformal planning technique, followed by a 10 Gy boost to the lumpectomy site. SGRT was used in daily setup for whole breast treatment that each patient’s breast was aligned with their reference breast surface generated from the planning computed tomography (CT) images via AlignRT system. Daily orthogonal kV imaging pair was then performed to confirm the treatment positioning by verifying the bony landmarks and the translational couch shifts were recorded for individual fraction. To evaluate the dosimetric implication, those shifts were further applied to the isocenter position of the original clinical treatment plan to represent a patient’s in-room position after kV imaging shifts. The dosimetric difference between the two setup methods, breast surface alignment vs. bony landmarks alignment, was then assessed on the original clinical plan and the new plan sum obtained from the 16 fractions where each one was recalculated with a new isocenter position. Boost fractions were excluded in this study, as setup was verified using surgical clips as the matching reference.
Results (tentative)
Translational shifts for the 30 patients (N = 480) were reviewed. The mean absolute shift in lateral, vertical and longitudinal directions was 0.22 cm (CI (95%): 0.19, 0.24; range: 0 to 1.98), 0.24 cm (CI (95%): 0.23, 0.26; range: 0 to 1.25) and 0.23 cm (CI (95%): 0.20, 0.25; range: 0 to 1.73), respectively. Dosimetric analysis revealed an average change of 1.13% in V95% coverage. The maximum coverage decreasing of 11% was observed in one patient, who had large shifts in both lateral and vertical directions which was possibly attributed to patient movements. Overall, the dosimetric outcome of both alignment references met the institutional clinical protocol with statistical significance.
Conclusion
These findings demonstrate the efficacy of a tattoo-less approach for breast cancer patients receiving whole breast RT.