Author: Ming Su, Yuenan Nancy Wang 👨🔬
Affiliation: Northeastern University, Hartford Healthcare 🌍
Purpose: High Z elements such as lead are often used to protect critical structures in clinical radiotherapy. Nanoparticles have different properties than bulk materials. We proposed a polymer matrix radiation shielding with Bismuth (Bi) nanoparticles packing, where the polymer-metal composites has narrow nanosize distribution (~5nm) with uniform dispersion of cellulose nanofibers, which enables strong affinity to interstitial space and provides effective radiation shielding. We aim to investigate the shielding efficiency of the proposed Bi nanoparticle polymer gel, which is lighter and more flexible than conventional shielding materials.
Methods: Cellulose nanofibers were prepared with TEMPO oxidation method using cellulose fibers, TEMPO, and NaBr and NaClO solution, where pH was adjusted at 10 by diluted HCl. Then cellulose nanofibers were centrifuged and purified by dialysis under ultrasonication. Bi nanoparticles were made using Bi(NO3)3·5H2O dissolved in deionized water in nitrogen atmosphere, followed by adding suspension of 20% (by mass) cellulose nanofibers. Polymer composites were made by adding dried nanoparticles into a mixture of PDMS prepolymer (10 parts) to complete polymerization. The Bi-nanoparticle based polymer layers were characterized using transmission electron microscope (TEM). The samples were placed on a clinically commissioned TrueBeam linac using 6~20MeV electron beams with a 10x10 cone and 100cm SSD. A calibrated GafChromic film was placed beneath the sample and above a 5cm solid water .
Results: Optical density difference was immediately observed between the Bi nanoparticle gel shielded film and the film without shielding. For 6MeV electron beam, the 5mm-thick polymer gel completed shielded the 6MeV electron beam, which made it equivalent to 3cm water or 2.7mm lead. However, the 5-mm nanoparticle based polymer gel was much lighter and flexible than 2.7mm lead layers.
Conclusion: We have proposed a light-weighted and flexible Bismuth nanoparticle based polymer for efficient shielding in electron radiotherapy.