Radiosensitivity

Radiosensitivity is the relative susceptibility of cells, tissues, organs or organisms to the harmful effect of ionizing radiation.

Cells types affected

Cells are least sensitive when in the S phase, then the G1 phase, then the G2 phase, and most sensitive in the M phase of the cell cycle. This is described by the 'law of Bergonié and Tribondeau', formulated in 1906: X-rays are more effective on cells which have a greater reproductive activity.[1][2]

From their observations, they concluded that quickly dividing tumor cells are generally more sensitive than the majority of body cells. This is not always true. Tumor cells can be hypoxic and therefore less sensitive to X-rays because most of their effects are mediated by the free radicals produced by ionizing oxygen.

It has meanwhile been shown that the most sensitive cells are those that are undifferentiated, well nourished, dividing quickly and highly active metabolically. Amongst the body cells, the most sensitive are spermatogonia and erythroblasts, epidermal stem cells, gastrointestinal stem cells.[3] The least sensitive are nerve cells and muscle fibers.

Very sensitive cells are also oocytes and lymphocytes, although they are resting cells and do not meet the criteria described above. The reasons for their sensitivity are not clear.

There also appears to be a genetic basis for the varied vulnerability of cells to ionizing radiation. This has been demonstrated across several cancer types and in normal tissues.[4][5]

Cell damage classification

The damage to the cell can be lethal (the cell dies) or sublethal (the cell can repair itself). Cell damage can ultimately lead to health effects which can be classified as either Tissue Reactions or Stochastic Effects according to the International Commission on Radiological Protection.

Tissue Reactions

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. Tissue reactions include skin reactions (epilation, erythema, moist desquamation), cataracts, circulatory disease, and other conditions.

Stochastic effects

Stochastic effects do not have a threshold of irradiation, are coincidental, and cannot be avoided. They can be divided into somatic and genetic effects. Among the somatic effects, secondary cancer is the most important. It develops because radiation causes DNA mutations directly and indirectly. Direct effects are those caused by ionizing particles and rays themselves, while the indirect effects are those that are caused by free radicals, generated especially in water radiolysis and oxygen radiolysis. The genetic effects confer the predisposition of radiosensitivity to the offspring.[6] The process is not well understood yet.

See also

References

  1. ↑ Bergonié, J.; Tribondeau, L. (1906). "De Quelques Résultats de la Radiotherapie et Essai de Fixation d'une Technique Rationnelle". Comptes-Rendus des Séances de l'Académie des Sciences. 143: 983–985.
  2. ↑ Bergonié, J.; Tribondeau, L. (1959). "Interpretation of Some Results of Radiotherapy and an Attempt at Determining a Logical Technique of Treatment / De Quelques Résultats de la Radiotherapie et Essai de Fixation d'une Technique Rationnelle". Radiation Research. 11 (4): 587–588. doi:10.2307/3570812.
  3. ↑ O. A. TROWELL: The sensitivity of lymphocytes to ionising radiation. In: The Journal of pathology and bacteriology. Band 64, Nummer 4, Oktober 1952, S. 687–704, ISSN 0368-3494. PMID 13000583.
  4. ↑ Yard, Brian D.; Adams, Drew J.; Chie, Eui Kyu; Tamayo, Pablo; Battaglia, Jessica S.; Gopal, Priyanka; Rogacki, Kevin; Pearson, Bradley E.; Phillips, James (2016-04-25). "A genetic basis for the variation in the vulnerability of cancer to DNA damage". Nature Communications. 7: 11428. ISSN 2041-1723. PMC 4848553 Freely accessible. PMID 27109210. doi:10.1038/ncomms11428.
  5. ↑ Barnett, Gillian C.; Coles, Charlotte E.; Elliott, Rebecca M.; Baynes, Caroline; Luccarini, Craig; Conroy, Don; Wilkinson, Jennifer S.; Tyrer, Jonathan; Misra, Vivek (2012-01-01). "Independent validation of genes and polymorphisms reported to be associated with radiation toxicity: a prospective analysis study". The Lancet. Oncology. 13 (1): 65–77. ISSN 1474-5488. PMID 22169268. doi:10.1016/S1470-2045(11)70302-3.
  6. ↑ Fornalski, K.W. (2016). "Radiation and evolution: from Lotka-Volterra equation to balance equation". International Journal of Low Radiation. 10 (3): 222–33. doi:10.1504/IJLR.2016.10002388.
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