The world is naturally radioactive and approximately 82% of human-absorbed radiation doses, which are out of control, arise from natural sources such as cosmic, terrestrial, and exposure from inhalation or intake radiation sources. In recent years, several international studies have been carried out, which have reported different values regarding the effect of background radiation on human health. Gamma radiation emitted from natural sources (background radiation) is largely due to primordial radionuclides, mainly ²³² Th and ²³⁸ U series, and their decay products, as well as ⁴⁰ K, which exist at trace levels in the earth's crust. Their concentrations in soil, sands, and rocks depend on the local geology of each region in the world. Naturally occurring radioactive materials generally contain terrestrial-origin radionuclides, left over since the creation of the earth. In addition, the existence of some springs and quarries increases the dose rate of background radiation in some regions that are known as high level background radiation regions. The type of building materials used in houses can also affect the dose rate of background radiations. The present review article was carried out to consider all of the natural radiations, including cosmic, terrestrial, and food radiation.

In the present study, AS1411 aptamer conjugated gold nanoclusters (GNCs) have been introduced as a targeted radiosensitizer for enhancing megavoltage radiation therapy efficacy.

Aim: Herein, the AS1411 aptamer-targeted ultrasmall gold nanoclusters (GNCs) were assessed at different aspects as a radiosensitizer. Materials & methods: AS1411 aptamer-conjugated gold nanoclusters (Apt–GNCs) efficacy was evaluated at cancer cells targeting, radiosensitizing effect, tumor targeting, and biocompatibility in breast tumor-bearing mice. Results: Flow cytometry and fluorescence microscopy exhibited more cellular uptake for Apt–GNCs in comparison with GNCs. In addition, inductively coupled plasma optical emission spectrometry results demonstrated its effective tumor targeting as the tumors’ gold content for GNCs and Apt–GNCs were 8.53 and 15.33 μg/g, respectively. Apt–GNCs significantly enhanced radiotherapy efficacy as mean tumors’ volume decreased about 39% and 9 days increase in the mice survival was observed. Both GNCs and Apt–GNCs were biocompatible. Conclusion: The Apt–GNCs is a novel and efficient radiosensitizer.

In recent years, there has been an increasing interest in using nanoparticles in the medical sciences. Today, metal nanoparticles have many applications in medicine for tumor visualization, drug delivery, and early diagnosis, with different modalities such as X-ray imaging, computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), etc., and treatment with radiation. This paper reviews recent findings of recent metal nanotheranostics in medical imaging and therapy. The study offers some critical insights into using different types of metal nanoparticles in medicine for cancer detection and treatment purposes. The data of this review study were gathered from multiple scientific citation websites such as Google Scholar, PubMed, Scopus, and Web of Science up through the end of January 2023. In the literature, many metal nanoparticles are used for medical applications. However, due to their high abundance, low price, and high performance for visualization and treatment, nanoparticles such as gold, bismuth, tungsten, tantalum, ytterbium, gadolinium, silver, iron, platinum, and lead have been investigated in this review study. This paper has highlighted the importance of gold, gadolinium, and iron-based metal nanoparticles in different forms for tumor visualization and treatment in medical applications due to their ease of functionalization, low toxicity, and superior biocompatibility.