Optimization of Radiation Shielding Considerations for Designing Halcyon Vault.

Purpose: To determine the radiation shielding considerations for optimization of Halcyon vault shielding requirements. Materials and Methods: 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 (TVLe) for 6 MV - flattening-filter-free (FFF) primary X-ray beam for ordinary concrete were measured. Results: 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 TVLe of 6 MV-FFF X-ray beam energy for ordinary concrete are found to be 33 and 29 cm, respectively. Conclusion: Using experimentally determined shielding considerations, the optimized vault shielding requirements for the Halcyon facility are calculated and a typical layout drawing is proposed.

STUDIES ON RADIATION SHIELDING PROPERTIES OF NEWLY DEVELOPED HIGH-DENSITY CONCRETE FOR ADVANCED RADIOTHERAPY FACILITIES.

The linear attenuation coefficients and tenth-value layers are determined experimentally for the newly developed Cement-based high-density Concrete and Fly-Ash-based Geopolymer high-density Concrete using Red-Mud-based synthetic aggregate made up from industrial waste. Linear attenuation coefficients were determined in narrow and broad beam conditions for five megavoltage X-ray photon beam energies, i.e. 6, 10, 15 MV, and 6 and 10 MV-FFF generated by Varian TrueBeam medical linear accelerator. These materials are found to be more effective in radiation shielding when compared with ordinary concrete and hematite ore-based high-density concrete making it a useful construction material for radiotherapy accelerator vaults. Similar values of linear attenuation coefficients are observed for all the above-mentioned X-ray beam energies when cement is replaced with fly-ash in ordinary concrete, hematite-based high-density concrete and red-mud-based high-density concrete, making it a good eco-friendly alternative of cement and useful for the construction of radiotherapy vaults.

Synthesis, Characterization, and Cytotoxicity Evaluation of Polyethylene Glycol-Coated Iron Oxide Nanoparticles for Radiotherapy Application.

BACKGROUND: Treatment methods for cancer that are widely being utilized affect both normal and cancerous cells. We report synthesis polyethylene glycol (PEG)-coated Fe3O4 nanoparticles (NPs) and its characteristic properties and appraise its potential as a promising radiation sensitizer candidate in radiotherapy that improves cancer treatment and reduces side effects of radiation. MATERIALS AND METHODS: PEG-coated Fe3O4 NPs were synthesized by chemical coprecipitation method and characterized by studying their size, structure, functional group, stability, magnetization, and cytotoxicity using different techniques. X-ray powder diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis results show that Fe3O4 NPs have been functionalized with PEG molecules during the course of synthesis. RESULTS: Synthesized NPs have good stability based on zeta-potential study. Dynamic light-scattering results reveal that PEG-coated Fe3O4 has a greater hydrodynamic size than bare Fe3O4. Transmission electron microscopy (TEM) micrograph exhibited that NPs are roughly spherical with size in range of 10-20 nm. Saturation magnetization value of PEG-coated and bare Fe3O4 also confirms coating and shows superparamagnetic behavior. Cytotoxicity evaluation study indicated that PEG-coated Fe3O4 is biocompatible on L929 and toxic on Michigan Cancer Foundation-7 (MCF-7) (breast cancer cells). CONCLUSION: These characterized properties of PEG-coated Fe3O4 NPs show that it could be used as a potential radiosensitizer candidate in radiotherapy to significantly improve cancer treatment and minimize painful side effects of radiation.