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Radioresistance is the level of ionizing radiation that organisms are able to withstand.. Ionizing-radiation-resistant organisms (IRRO) were defined as organisms for which the dose of acute ionizing radiation (IR) required to achieve 90% reduction (D10) is greater than 1,000 gray (Gy) [1]
Deinococcus radiodurans is a bacterium, an extremophile and one of the most radiation-resistant organisms known. It can survive cold, dehydration, vacuum, and acid, and therefore is known as a polyextremophile.
Renal cell cancer and melanoma are generally considered to be radioresistant but radiation therapy is still a palliative option for many patients with metastatic melanoma. Combining radiation therapy with immunotherapy is an active area of investigation and has shown some promise for melanoma and other cancers.
Tissue reactions have a threshold of irradiation under which they do not appear and above which they typically appear. Fractionation of dose, dose rate, the application of antioxidants and other factors may affect the precise threshold at which a tissue reaction occurs.
The oxygen effect has particular importance in external beam radiation therapy where the killing of tumour cells with photon and electron beams in well oxygenated regions can be up to three times greater than in a poorly vasculated portion of the tumour.
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Deinococcus (from the Greek: δεινός, deinos, "dreadful, strange" and κόκκος, kókkos, "granule" [1]) is in the monotypic family Deinococcaceae, and one genus [2] of three in the order Deinococcales [3] [4] of the bacterial phylum Deinococcota highly resistant to environmental hazards.
[12] [6] Pratx and Kapp, 2019, suggest that stem cells which reside in a hypoxic niche are relatively radioresistant, but whenever surrounding tissue is damaged, the stem cells become more oxygenated and therefore more radiosensitive. [12]