Occupational radiation exposure and excess additive risk of cataract incidence in a cohort of US radiologic technologists

Abstract

Objectives: Previous analyses of cataract in radiation-exposed populations have assessed relative risk; radiogenic excess additive risk (EAR), arguably of more public health importance, has not been estimated. Previous analysis of a large prospective cohort of US radiologic technologists (USRT) quantified excess relative risk of cataract in relation to occupational radiation dose. We aim to assess EARs of cataract.

Methods: We estimated EARs of cataract/cataract surgery in the USRT cohort using generalised additive models in relation to occupational radiation exposure, and assessed risk modification by a priori-selected cataract risk factors (diabetes, body mass index, smoking, race, sex, birth-year, ultraviolet B (UVB) radiation exposure).

Results: There were 11 345 cataract diagnoses and 5440 of cataract surgery during 832 462 and 888 402 person-years of follow-up, respectively. Cumulative occupational radiation exposure was associated with self-reported cataract, but not with cataract surgery, with EAR/10⁴ person-year Gy=94 (95% CI: 47 to 143, p<0.001) and EAR/10⁴ person-year Gy=13 (95% CI: <0 to 57, p=0.551), respectively. There was marked (p<0.001) variation of EAR by age and by diabetes status, with risk higher among persons ≥75 years and diabetics. There were indications of elevated risk among those with higher UVB radiation (p=0.045), whites (p=0.056) and among those with higher levels of cigarette smoking (p=0.062). Elevated additive risk was observed for estimated occupational radiation eye-lens doses <100 mGy (p=0.004) with no dose-response curvature (p=0.903).

Conclusions: The elevated additive risks associated with low-dose radiation, if confirmed elsewhere, have important public health and clinical implications for radiation workers as well as regulatory measures.

Keywords: diabetes mellitus; ionising radiation; ophthalmology; public health; visual defects.

Figure 1.. Adjusted additive excess risk as a function of occupational dose, for self- reported history of diagnosis of cataract (plot a) and cataract surgery (plot b) (+95% CI).^a

^aRisks for cataract are evaluated using a model with factor terms in the background (zero-dose) model for sex, baseline diabetes status, baseline smoking status, baseline numbers of cigarettes per day, baseline age at stopped smoking, and continuously adjusted for ln[age], ln[age]², ln[age]³, [birth date], [birth date]², [birth date]³, (time varying) cumulative UVB radiant exposure (including missingness), baseline BMI (including missingness), BMI², BMI³, BMI⁴, BMI⁵, year (of follow-up), year², year³, year⁴, year⁵, year⁶. For cataract surgery the indicated model uses adjustments for sex, baseline diabetes status, baseline smoking status, baseline numbers of cigarettes per day, baseline age at stopped smoking, and continuously adjusted for ln[age], ln[age]², ln[age]³, ln[age]⁴, [birth date], [birth date]², (time varying) cumulative UVB radiant exposure (including missingness), baseline BMI (including missingness), BMI², year (of follow-up), year², year³, year⁴, year⁵, year⁶.

Figure 2.. Adjusted additive risk as a function of age (plot a), and radiation associated excess risk (per 10⁴ person year Gy) (plot b) as a function of age, for self-reported history of diagnosis of cataract (+95% CI).

^aRisks are evaluated using a model with factor terms in the background (zero-dose) model for age, sex, diabetes status, smoking status, baseline smoking status, baseline numbers of cigarettes per day, baseline age at stopped smoking, and continuously adjusted for cumulative UVR radiant exposure (including missingness), baseline BMI (including missingness), BMI², BMI³, BMI⁴, BMI⁵, year, year², year³, year⁴, year⁵, year⁶.