Malignant tumors are one of the main causes of human death. The clinical treatment of malignant tumors is usually surgery, chemotherapy, radiotherapy, and so forth. Radiotherapy, as a traditional and effective treatment method for cancer, is widely used in clinical practice, but the radiation resistance of tumor cells and the toxic side effects to normal cells are still the Achilles heel of radiotherapy. Multifunctional inorganic high-atom nanomaterials are expected to enhance the effect of tumor radiotherapy. Tungsten and bismuth, which contain elements with high atomic coefficients, have strong X-ray energy attenuation capability. We synthesized Bi 2 WO 6 nanosheets (NSs) using a hydrothermal synthesis method and modified polyvinylpyrrolidone (PVP) on their surface to make them more stable. PVP–Bi 2 WO 6 NSs have a variety of effects after absorbing X-rays (such as the photoelectric effect and Compton effect) and release a variety of particles such as photoelectrons, Compton electrons, auger electrons, and so forth, which can react with organic molecules or water in cells, generate a large number of free radicals, and promote cell apoptosis, thereby improving the effect of radiotherapy. We show through γ-H2AX and DCFH-DA probe analysis experiments that PVP–Bi 2 WO 6 NSs can effectively increase cell DNA damage and reactive oxygen species formation under X-ray irradiation. Clone formation analysis showed that PVP–Bi 2 WO 6 NSs can effectively suppress cell colony formation under X-ray irradiation. These versatile functions endow PVP–Bi 2 WO 6 NSs with enhanced radiotherapy efficacy in animal models. In addition, PVP–Bi 2 WO 6 NSs can also be used as contrast agents for X-ray computed tomography (CT) imaging with obvious effects. Therefore, PVP–Bi 2 WO 6 NSs can be used as CT imaging contrast agents and tumor radiotherapy sensitizers and have potential medical applications.

Oral cancer is the most common malignant tumor in the oral and maxillofacial region, which seriously threatens the health of patients. At present, radiotherapy is one of the commonly used methods for oral cancer treatment. However, the resistance of cancerous tissues to ionizing radiation, as well as the side effects of X-rays on healthy tissues, still limit the application of radiotherapy. Therefore, how to effectively solve the above problems is still a challenge at present. Generally speaking, elements with high atomic numbers, such as bismuth, tungsten, and iodine, have a high X-ray attenuation capacity. Using nanomaterials containing these elements as radiosensitizers can greatly improve the radiotherapy effect. At the same time, the modification of nanomaterials based on the above elements with the biocompatible polymer can effectively reduce the side effects of radiosensitizers, providing a new method for the realization of efficient and safe radiotherapy for oral cancer. In this work, we prepared Tween-20-modified BiVO 4 nanorods (Tw20-BiVO 4 NRs) and further used them in the radiotherapy of human tongue squamous cell carcinoma. Tw20-BiVO 4 NRs are promising radiosensitizers, which can generate a large number of free radicals under X-rays, leading to the damage of cancer cells and thus playing a role in tumor therapy. In cell experiments, radiotherapy sensitization of Tw20-BiVO 4 NRs significantly enhanced the production of free radicals in oral cancer cells, aggravated the destruction of chromosomes, and improved the therapeutic effect of radiotherapy. In animal experiments, the strong X-ray absorption ability of Tw20-BiVO 4 NRs makes them effective contrast agents in computed tomography (CT) imaging. After the tumors are located by CT imaging, it helps to apply precise radiotherapy; the growth of subcutaneous tumors in nude mice was significantly inhibited, confirming the remarkable effect of CT imaging-guided radiotherapy.