Author: Awens Alphonse, Nebi Demez, Noufal Manthala Padannayil, Haley Park, Shyam Pokharel, Suresh Rana, Lauren A. Rigsby, Nishan Shrestha, Somol Sunny 👨🔬
Affiliation: Florida Atlantic University, Lynn Cancer Institute, Boca Raton Regional Hospital, Baptist Health South Florida 🌍
Purpose: This study evaluates the dosimetric effects of patient positioning errors, including setup inaccuracies and yaw deviations, on dual-isocenter volumetric modulated arc therapy (VMAT) plans for bilateral breast cancer.
Methods: A dual-isocenter VMAT technique using two partial arcs per breast with collimator adjustments was developed to enhance dose conformity and reduce field overlap. Positional uncertainties, including yaw deviations (±1°, ±2°, ±3°), isocenter shifts (±5 mm), and their combinations, were simulated, generating 49 dose distributions. Dosimetric impacts were assessed for clinical target volumes (CTVs) and organs at risk (OARs), including the heart, lungs, esophagus, skin, and left anterior descending artery (LAD).
Results: Yaw errors caused minimal dosimetric deviations, with CTV coverage (V95) decreasing by up to 0.21%. For OARs, yaw errors moderately increased the mean dose to the LAD, heart, and esophagus. Lung dose metrics (V20 and V5) showed negligible changes, while Skin Dmax exhibited minor variations. In contrast, setup errors had a greater impact. CTV_Breast_L experienced the largest reduction in V95, decreasing by up to 5.5%. The mean dose to the LAD, heart, and esophagus increased by 40%, 31%, and 16%, respectively. Lung V20 and V5 rose by 25% and 6.4%, and Skin Dmax increased by 3%. Combined yaw and setup errors slightly amplified deviations. The mean dose to the LAD and heart increased by an additional 1.23% and 1.57%, respectively, compared to setup errors alone, while esophagus doses displayed smaller increases (<1%). Lung and Skin metrics varied by less than 0.5% compared to setup errors.
Conclusion: Setup inaccuracies caused greater dosimetric impacts than yaw deviations, reducing target coverage and increasing OAR doses. Combined errors further amplified deviations. Precise patient alignment and robust verification protocols are critical to maintain dosimetric precision in dual-isocenter VMAT plans for bilateral breast cancer. Further validation is needed with larger patient cohorts.