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Comparison of Setup Uncertainty Using AlignRT-Guided and RPM-Guided DIBH for Left-Sided Breast Irradiation

W Lu*, G Li , E Gillespie , L HONG , E Yorke , J Mechalakos , M Hunt , S Powell , X Tang , Memorial Sloan Kettering Cancer Center, New York, NY


(Tuesday, 7/31/2018) 3:45 PM - 4:15 PM

Room: Exhibit Hall | Forum 6

Purpose: To compare the setup uncertainty using AlignRT-guided and RPM-guided DIBH for left breast irradiation. We measured setup uncertainty in both central lung distances and heart to field edge distances.

Methods: Twenty left-sided breast DIBH patients (10 RPM and 10 AlignRT) were retrospectively evaluated. The tangential DRR and MV portal images were used. Each patient had 4 to 7 portal images available. Two distances on each image were measured: 1) the central lung distance (inner thoracic wall to dorsal field edge, representing the amount of lung in the field); and 2) the distance from anterior heart shadow to dorsal field edge. The differences of the distances between the MV portal image and corresponding DRR were measured to evaluate the setup uncertainties. The (mean difference, absolute difference, and the standard deviation) of the portal images over all patients were calculated and reported in the same order in parentheses.

Results: For the central lung distance, the setup uncertainties are (0.03, 0.12, 0.24) cm for RPM, and (-0.12, 0.14, 0.17) cm for AlignRT, with P-values (0.001, 0.53, 0.21). For the heart to field edge distance, the setup uncertainties are (-0.49, 0.52, 0.27) cm for RPM, and (-0.07, 0.30, 0.33) cm for AlignRT, with P-values (<0.001, 0.01, 0.43). A negative value indicated that the heart moved closer to the field edge.

Conclusion: Both AlignRT and RPM guided DIBH showed similar uncertainties for the central lung distance. For the heart to field edge distance, AlignRT showed significantly smaller uncertainty. This might indicate that the heart position/motion is more correlated to the external surface motion captured by AlignRT than to the sup-inf motion captured by RPM. For the central lung distance, the correlations to the surface motion and sup-inf motion are similar.


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