Optimization of Radiation Shielding Considerations for Designing Halcyon Vault

To determine the radiation shielding considerations for optimization of Halcyon vault shielding requirements.

The primary and leakage workloads were estimated using actual clinical treatment planning and treatment delivery data acquired from three busy operational clinical Halcyon facilities. The effective use factor was determined based on a newer approach proposed in this paper using the percentage of patients treated with different treatment techniques. The transmission factor of the primary beam block, maximum head leakage, and patient scatter fractions around the Halcyon machine were experimentally determined. The first tenth-value layer (TVL₁) and equilibrium tenth-value layer (TVL_e) for 6 MV - flattening-filter-free (FFF) primary X-ray beam for ordinary concrete were measured.

The primary and leakage workloads are estimated as 1 × 10⁵ cGy/wk and 3.1 × 10⁵ cGy/wk at 1 m respectively. The effective use factor is found as 0.114. The primary beam-block transmission factor is determined as 1.7 × 10^-4 at 1 m distance from isocenter along the central beam axis. The maximum head leakage is noted as 6.23 × 10^-4. The patient scatter fractions are reported for various planar angles around the Halcyon machine at a radial distance of 1 m in a horizontal plane passing through isocenter. The TVL₁ and TVL_e of 6 MV-FFF X-ray beam energy for ordinary concrete are found to be 33 and 29 cm, respectively.

Using experimentally determined shielding considerations, the optimized vault shielding requirements for the Halcyon facility are calculated and a typical layout drawing is proposed.