Noncancer Effects of Ionizing Radiation Exposure on the Eye, the Circulatory System and beyond: Developments made since the 2011 ICRP Statement on Tissue Reactions

Abstract

For radiation protection purposes, noncancer effects with a threshold-type dose-response relationship have been classified as tissue reactions (formerly called nonstochastic or deterministic effects), and equivalent dose limits aim to prevent occurrence of such tissue reactions. Accumulating evidence demonstrates increased risks for several late occurring noncancer effects at doses and dose rates much lower than previously considered. In 2011, the International Commission on Radiological Protection (ICRP) issued a statement on tissue reactions to recommend a threshold of 0.5 Gy to the lens of the eye for cataracts and to the heart and brain for diseases of the circulatory system (DCS), independent of dose rate. Literature published thereafter continues to provide updated knowledge. Increased risks for cataracts below 0.5 Gy have been reported in several cohorts (e.g., including in those receiving protracted or chronic exposures). A dose threshold for cataracts is less evident with longer follow-up, with limited evidence available for risk of cataract removal surgery. There is emerging evidence for risk of normal-tension glaucoma and diabetic retinopathy, but the long-held tenet that the lens represents among the most radiosensitive tissues in the eye and in the body seems to remain unchanged. For DCS, increased risks have been reported in various cohorts, but the existence or otherwise of a dose threshold is unclear. The level of risk is less uncertain at lower dose and lower dose rate, with the possibility that risk per unit dose is greater at lower doses and dose rates. Target organs and tissues for DCS are also unknown, but may include heart, large blood vessels and kidneys. Identification of potential factors (e.g., sex, age, lifestyle factors, coexposures, comorbidities, genetics and epigenetics) that may modify radiation risk of cataracts and DCS would be important. Other noncancer effects on the radar include neurological effects (e.g., Parkinsonʼns disease and dementia) of which elevated risk has increasingly been reported. These late occurring noncancer effects tend to deviate from the definition of tissue reactions, necessitating more scientific developments to reconsider the radiation effect classification system and risk management. This paper gives an overview of historical developments made in ICRP prior to the 2011 statement and an update on relevant developments made since the 2011 ICRP statement.

Cancer and Non-Cancer Effects Following Ionizing Irradiation

“…A growing body of epidemiological evidence has suggested elevated radiation risks of cardiovascular diseases (especially ischemic heart disease and stroke) [ 30 , 31 , 32 , 33 ]; however, the manifestations (in particular at low or moderate doses, and at low dose rates) and mechanistic underpinnings of this remain incompletely understood [ 9 , 34 , 35 ]. Nabialek-Trojanowska et al [ 12 ] carried out speckle-tracking echocardiography in 12 patients at a median of 51 months after radiotherapy for mediastinal lymphoma, concluding that radiation exposure of the heart substructures is correlated with cardiac dysfunction (e.g., left ventricular global or anterior longitudinal strain).…”

“…Regarding the effects of radiation exposure on the eye, evidence has accumulated for cataracts following moderate or high doses [ 37 , 38 , 39 ] (along with limited evidence at low doses [ 40 , 41 ]) and neovascular glaucoma following high doses [ 9 ]. Azizova et al [ 19 ] reported a significantly increased radiation risk of normal-tension glaucoma (a subtype of primary open-angle glaucoma) in a cohort of Russian Mayak nuclear workers, confirming observations in Japanese atomic bomb survivors [ 42 , 43 , 44 ].…”

“…Ionizing radiation is used to treat cancer [ 1 , 2 ], but is also a carcinogen [ 3 , 4 ]. Alongside that, there has been mounting interest not only in radiotherapy for non-cancer diseases [ 5 , 6 , 7 , 8 , 9 ], but also the non-cancer effects of radiation exposure that occur at doses or dose rates much lower than previously suggested or considered [ 9 , 10 , 11 ]. This underlines the need to consider both the cancer and non-cancer effects of medical (diagnostic or therapeutic), occupational or environmental exposure to radiation.…”

Nuclear Medicine Radiological Hot Laboratory Simulation: A Mixed-Method Intervention Study on Immersive Virtual Reality for Sustainable Education

“…A study by Boice et al determined that 109,019 medical professionals linked with radiation procedures between 1965 and 1994 were at an elevated risk for lung cancer [6]. In the healthcare environment, occupational radiation exposure is well-established as a factor that elevates cancer risk and contributes to premature vascular aging and cataract formation [7].…”