SU‐E‐J‐56: Surface Imaging for Breast Patients

Abstract

Purpose: Compares surface imaging (SI) to MV films for positioning of 13 patients receiving whole‐breast irradiation. Methods: AlignRT v5.0 was used to capture non‐gated, 3D surface images during filmed fractions (n=55) after positioning with skin marks and correction for rotations. Registrations of SI to a reference surface, generated from 3mm‐thick CT data, were analyzed off‐line for both the “entire” and the “breast” regions. MV films were compared to digitally‐reconstructed radiographs generated from the same CT dataset. The group mean, systematic error (σ), and random error (g) were calculated for positioning with MV and SI both before and after positioning correction. The 95% limits of agreement (LOA) were used for statistical comparisons. Results: Inter‐fraction systematic/random errors calculated from MV filming were 1.6/2.1mm (Anterior‐Posterior), 2.9/3.0mm (Cranio‐Caudal), and 2.4/4.1mm (Left‐Right), resulting in a setup margin of 5.5/9.4/9.0mm in AP/CC/LR dimensions using the van Herk formulation. Registering the “entire” and “breast” surfaces acquired before MV positioning correction resulted in setup margins that were larger by 1.6– 3.3mm in AP/LR but smaller by 0.4–0.6mm in CC direction, thereby indicating comparable inter‐fraction errors. After positioning with films, group means for the “entire” surface decreased by 0.5–2mm and the systematic/random errors decreased by 0.3–0.9mm. In contrast, group mean for “breast” increased in the CC direction. The LOA showed large discrepancies between the two modalities (smallest:‐3.5 to 10.3mm along AP for “entire”, largest:‐11.3 to 9.9mm along CC for “breast”). Conclusion: This study shows that the two modalities provide comparable systematic/random errors for breast positioning. However, MV positioning of bony anatomy led to a consistent cranio‐caudal offset (i.e., larger group mean) from the position indicated by AlignRT probably due to deformation of the breast tissue. These results suggest that the use of MV and SI should be integrated to ensure simultaneous coverage of chestwall and soft tissue targets.