ABSTRACT
The unique interaction of X-rays with nanostructured materials offers many new opportunities for enhancement of the efficacy of the use of X-radiation. Materials with high atom and electron density lead to enhanced scattering or absorbance of X-rays acting thus as radiosensitizers and causing increased localized and targeted damage to cancer cells. Nanotechnology approaches can enable implants currently used for radiation therapy guidance to also deliver drugs to the tumor. High-Z NPs can be used as computed tomography (CT) contrast agents. Nanostructured materials offer new ways to develop micro-sources of X-ray beams.Here we review some of the key areas where important developments have occurred recently in the use of X-rays and
Keywords: nanotechnology, radiation oncology, nanotubes, nanoparticles, image guided radio therapy, gold, DNA, X-ray, radiosensitizer, nanocoated, implant, drug release profile, radiation therapy, dose enhancement, nanotechnology, image guided, energy deposition, tumor, chemoradiation therapy
nanostructured materials for radiation oncology. The various applications discussed are as follows: (1)gold NPs for enhanced radiation therapy (2) nanoparticles as delivery agents for radiation sensitizers (3)nano-coated drug-loaded implants for biologically in situ enhanced, image-guided radio therapy (BIS-IGRT) (4)nanoparticles as imaging agents for radiation therapy; and (5) nanotechnology for radiation sources.X-rays have been used extensively in medicine for diagnosis and therapy since their discovery. In radiation oncology, X-rays act directly by altering or damaging biomolecules such as DNA, and also indirectly by the generation of free radicals that can destroy malignant cells. X-rays are attractive in oncology because they penetrate much deeper than optical electromagnetic waves, thus offering access to deep tumors. Today more than 60% of tumors are treated with radiation, usually as an adjuvant to chemotherapy and resection.The unique interaction of X-rays with nanostructured materials offers many new opportunities for enhancement of the efficacy of radiation therapy using nanomaterials. Materials with high atom and electron density lead to enhanced scattering or absorbance of X-rays acting thus as radiosensitizers and causing increased localized and targeted damage to cancer cells. High-Z NPs can be used as computed tomography (CT) contrast agents. Nanostructured materials offer new ways to develop micro-sources of X-ray beams. Here we review some of the key areas where important developments have occurred recently in the use of X-rays and nanostructured materials for diagnosis and therapy. 43.1 Gold Nanoparticles for Radiation TherapyClinical radiation therapy of cancer is generally performed by either externally produced high-energy (MeV) photons or electrons, or internally placed radioactive isotopes emitting low-energy (keV) photons. For both treatment modalities, the therapeutic benefit is defined as the radiation dose to the cancer cells divided by the radiation dose to the normal tissue. The goal of radiation oncology treatment planning is the maximization of this ratio. At a certain point, particularly for external beam radiation therapy, increases
in radiation dose to the target volume are limited by toxicity to the normal tissue. For many disease sites, the maximum tolerable dose falls short of that which would provide the best therapeutic response.Gold NPs have been investigated as platforms to carry drugs or radiosensitizing agents to tumors due to the biocompatibility of gold and relative ease of conjugation with therapeutic and tar-geting moieties. Recently, there has been interest in exploiting the physical properties of gold, specifically the high atomic number, to enhance radiation therapy. Localized X-ray absorption and localized energy deposition at the nanoscale can be achieved from low-energy electrons released from nanostructures interacting with hard X-ray radiation in aqueous solution through three key mechanisms: (1) localized absorption of X-rays by nanostructures, (2) effective release of low-energy electrons from small nanostructures (Fig. 43.1), and (3) efficient deposition of energy in water in the form of radicals and electrons. [1]
Figure 43.1 (Up) Schematic of interaction of X-rays with gold nano-particles and resulting damage to endothelial cells for radiation therapy. From ref. [7]. (Down) Photoelectric absorption cross section shown as a function of incident photon energy for gold. From ref. [2] with permission.
