Perspectives Ionizing radiation exposure and the development of intervertebral disc degeneration—no case to answer Fiona E. Mellor, BSc (Hons)*, Alexander C. Breen, MSc, BSc (Hons) Institute for Musculoskeletal Research and Clinical Implementation, Anglo-European College of Chiropractic, 13-15 Parkwood Rd, Bournemouth, BH5 2DF, United Kingdom Received 5 April 2012; accepted 6 July 2012 In the following perspective article, Mellor and Breen provide a counterpoint to a previous perspec- tive on the potential link between ionizing radiation exposure and intervertebral disc degeneration in humans [1]. The previous perspective asked, is this link a myth or reality? It suggested the po- tential for such a link. Mellor and Breen offer a drastically alternate view, in essence, that the ques- tion itself is flawed. To support their perspective, they explain the different units of radiation measurement and their conversion to risk in humans and how this impacts the previous perspective. They explain the variable sensitivity of different body tissues to radiation and highlight that neither human research nor any of the multiple international regulatory agencies have ever suggested that the intervertebral disc is sensitive to radiation. Finally, they claim that it is impossible to predict with any certainty the effects of low-level radiation on the intervertebral discs. Ó 2013 Elsevier Inc. All rights reserved. Keywords: Disc degeneration; Radiation dose; Imaging; Spine; Back pain In response to Samartzis and Cheung’s discussion, ‘‘Ion- izing radiation exposure and the development of interverte- bral disc degeneration in humans: myth or reality’’ [1], the authors state they are raising the issue to address the burden of proof as to whether radiation exposure at low-to- moderate levels is related to disc degeneration. They refer to high levels of radiation as being greater than 5 gray (Gy), moderate levels as 1 Gy, and low levels as less than 0.5 Gy. However, quoting the absorbed dose does not con- sider the fact that tissues in the body vary in their sensitivity to radiation and therefore the risk of radiation-induced ef- fects. To understand this, you need to know the effective dose, for which the SI unit is Sieverts (Sv), and which takes into account both the type of radiation (X-rays, gamma, alpha, and so forth) and the sensitivity of tissue being irra- diated (tissue weighting factors). Confusingly, many studies do not make this distinction, hence radiation doses for many medical examinations may be quoted in either Gy or Sv. Low-to-moderate levels of radiation are defined by the International Commission on Radiological Protection (ICRP) for research purposes as those that impart an effec- tive dose of between 1 and 10 milliSieverts (mSv) [2]. In the United Kingdom, the average background radiation dose per annum is 2.2 mSv (and up to 7.5 mSv for those living in Radon rich areas, such as Cornwall). It is known that radiation exposure has a biological effect, but the rela- tionship between intensity and effects are complex. The de- terministic effects that include cataracts, desquamation, decreased white blood cell count, erythema, fibrosis, organ atrophy, and sterility are only seen at much higher doses and have an individual dose threshold. The stochastic effects, such as cancer and genetic defects in offspring, however, do not have a dose threshold, although their prob- ability increases with increasing dose. There is growing ev- idence of other radiation-associated consequences, such as heart disease, stroke, digestive disorders, and respiratory diseases [3]; however, the international agencies that mon- itor and assess radiation including the Health Protection FDA device/drug status: Not applicable. Author disclosures: FEM: Fellowship Support: National Institute for Health Research Clinical Academic Fellowship (F, Paid directly to institu- tion/employer). ACB: Nothing to disclose. The disclosure key can be found on the Table of Contents and at www. TheSpineJournalOnline.com. * Corresponding author. Institute for Musculoskeletal Research and Clinical Implementation, Anglo-European College of Chiropractic, 13-15 Parkwood Rd, Bournemouth, BH5 2DF, United Kingdom. Tel.: þ44 (0) 1202-436280. E-mail address: imrci.fmellor@aecc.ac.uk (F.E. Mellor) 1529-9430/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.spinee.2012.07.039 The Spine Journal 13 (2013) 224–228