Development of a Linac Vault Shielding Calculation Tool
Abstract
Purpose
Shielding design for medical linear accelerator (LINAC) vaults is commonly performed using spreadsheet-based implementations of NCRP Report No. 151. While effective, these approaches are limited by fixed calculation points and restricted geometric flexibility. This work presents the development of a standalone application that performs NCRP-based LINAC shielding calculations using two-dimensional (2D) vault modeling combined with a ray-tracing–based computational framework.
Methods
A standalone software application was developed to calculate shielding requirements for primary barriers, secondary barriers, ceilings, mazes, and doors. User inputs include vault dimensions, LINAC workload, beam energy, use and occupancy factors, and shielding materials such as concrete, steel, and lead. Vault geometry is represented in 2D across the three cardinal planes. A ray-tracing algorithm propagates radiation paths from the source LINAC head to standard NCRP reference points as well as user-defined locations. Each ray is segmented by intersected shielding materials, and cumulative attenuation and resulting dose are computed along the path.
Results
For standard vault configurations, calculated shielding thicknesses and dose estimates were consistent with conventional spreadsheet-based NCRP 151 calculations. The 2D ray-tracing framework enabled flexible evaluation of shielding performance at arbitrary locations within each cardinal plane and supported mixed-material barriers and non-standard geometries that are difficult to evaluate using spreadsheet methods alone. The application was verified by comparison with our spreadsheet-based hand calculations. All key points are within 1% differences.
Conclusion
This standalone application enhances traditional NCRP-based LINAC shielding calculations by integrating 2D geometric modeling and ray tracing, enabling more flexible and spatially resolved analysis while maintaining consistency with established methodology. Extension to full three-dimensional vault modeling is currently under development.