Thyroid dose and cancer risk from head and neck computed tomography at two selected centres in Nigeria

Abstract

Objective: The objective of this study was to evaluate the thyroid glands' radiation dose and the risk of thyroid cancer induction from head or neck computed tomography (CT) examinations. Methods: In a prospective study, we evaluated all participants of all ages and sex referred for Head or Neck CT Scan at the University College Hospital, Ibadan and Me Cure Healthcare Limited, Ibadan, Oyo State, Nigeria. Thyroid radiation dose was estimated with impact scan calculator, and real-time dose measurement with thermoluminescent badge dosimeters (TLDs). Data were analysed and P < 0.05 was considered statistically significant. Results: One hundred and sixty-three participants (128 adults and 35 children) participated in the study. In most participants (74%), the tube voltage was 120 kVp. The estimated median thyroid gland dose by the imPACT scan calculator was 4.95 mGy (range = 1.20–30.0 mGy) and 4.40 mGy (range = 3.0–5.10 mGy), while the real-time dose measured by the TLD was 4.79 mGy (range = 1.73–96.7 mGy) and 2.33 mGy (range = 1.20–3.73 mGy) at Centre A and B, respectively. The estimated median thyroid cancer risk was 2.88 × 10−6 (maximum range of 52 × 10−6) at centre A and a median value of 3.20 × 10−6 with a cancer risk estimate that may reach 17.9 × 10−6 recorded at centre B, compared to a cumulative thyroid cancer risk of 0.12 × 10−5 among the general Nigerian population. Conclusions: Scanner specifications and technique may significantly contribute to variations seen in thyroid radiation doses. There may be a need to optimise centre protocols and apply dose reference levels for head and neck CT examinations to reduce thyroid cancer risk in Nigeria.

Keywords

• computed tomography
• impact scan calculator
• ionising radiation
• monte carlo
• paediatric
• thermoluminescent dosimeters
• thyroid dose