Standardizing Metallic Port HU Overrides for Breast Tissue Expanders
Abstract
Purpose
High-density metallic ports in breast tissue expanders (TE) introduce CT artifacts that cause dose calculation uncertainties for postmastectomy radiation planning. TE ports have either a titanium or stainless-steel needle guard and a very high-z magnet. Materials and dimensions vary by vendor. With no clinical standardization, HU overrides will vary depending on the planner or physicist. Our goal was to identify a repeatable and practical approach for port overrides that produce clinically acceptable dose distributions.
Methods
Six patients (two per TE type) were retrospectively selected: Allergan Natrelle 133s, Mentor Artoura, and Sientra AlloX2 TE and planned with 3D and VMAT. Using the vendor-specified dimensions and materials, three override strategies were investigated: (i) separate magnet and needle guard density overrides, (ii) combined magnet and needle guard overrides, and (iii) override the entire port to water-equivalent density. Plans were re-calculated and assessed for each method using maximum dose, skin dose, and chest wall dose.
Results
Dose maxima were consistent across the methods per each patient. Methods i and ii consistently displayed similar dosimetric outcomes, with colder regions around the port and 95% isodose coverage behind the port. Method iii generally produced higher hot spots, with most of the dose differences being highly localized within the saline volume. Method iii also had higher variability of dose within the chest wall and locally around the port. Skin and chest wall doses were method- and expander-dependent, with AlloX2 showing the largest variability. Across all cases, heart and lung doses remained comparable. These results were consistent for VMAT and 3D.
Conclusion
Methods i and ii demonstrated better dosimetric outcomes than iii. Method ii is recommended since it is as dosimetrically effective as Method i, while being more reproducible and less time-consuming to contour. This provides a standardized repeatable and practical approach for port HU overrides.