Author: Shae Gans, Carri K. Glide-Hurst, Mark Pankuch, Chase Ruff, Niek Schreuder, Nicholas R. Summerfield, Yuhao Yan 👨🔬
Affiliation: Departments of Human Oncology and Medical Physics, University of Wisconsin-Madison, Northwestern Medicine Proton Center, Northwestern Medicine Chicago Proton Center, Leo Cancer Care 🌍
Purpose: Novel upright patient positioners coupled with diagnostic-quality vertical CT at treatment isocenter introduce a significant opportunity for improved image-guided particle therapy. Treating patients upright increases lung volumes, reduces tumor motion, and improves lung/whole-heart (WH) sparing. Yet, dose to cardiac substructures (CS) is strongly associated to outcomes as compared to WH metrics. This work investigates applying a novel deep-learning (DL) segmentation pipeline to upright radiation therapy (RT) for enhanced CS sparing as compared to supine geometry.
Methods: Seven patients underwent thoracic proton RT, acquiring paired CT images in supine and upright positions. Our pre-trained DL pipeline with an nnU-Net backbone generated 13 CS (WH/chambers/great vessels/coronary arteries) on both datasets and were corrected by an anatomical expert. DL performance was evaluated by Dice similarity coefficients (DSCs) between predicted and corrected contours. To measure geometric differences between normal anatomy (lungs/WH/CS) and target volumes (GTV/CTV), Lungs/WH volume ratios and CS centroid displacement between registered positions were calculated. Evaluation of two ultra-central lung cancer patients was performed for CS displacements relative to the target via dose-volume-histograms (DVHs) comparisons from clinical dose distributions.
Results: DL successfully predicted CS for both supine and upright orientations (DSC =0.79±0.16 and 0.72±0.22, respectively). Upright lung volumes increased by a median 19.4% (range: -8.9/42.8%) whereas WH decreased by 4% (range: -3.6/9.5%). Upright geometry yielded inferior shifts for all CS (median 21.9mm, range: 10.0/39.2mm) with ~50% of CS shifting >5mm anterior, and ~80% of CS shifting right although with smaller magnitude (median 3.2mm (range: -8.7/9.3mm)). Increased displacements between tumors and CS were observed, leading to demonstrable changes in cardiac sparing in the DVHs.
Conclusion: Our initial results suggest that CS exhibit >2cm shift inferior in the upright orientation with additional displacements toward the anterior and right, suggesting strong potential for upright RT to yield favorable geometries to support advanced cardiac sparing.