F Andraws Yalda1,2, J Holroyd3, M Islam4, C Theodorakou1,5, K Horner1. 1. Division of Dentistry, School of Medical Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester Academic Health Science Centre, Manchester M13 9PL. 2. College of Dentistry, Hawler Medical University, Erbil, Iraq. 3. Dental X-ray Protection Services, Public Health England, Oak Park Lane, Cookridge, Leeds, LS16 6RW. 4. Faculty of Biology, Medicine and Health, The University of Manchester, Manchester Academic Health Science Centre, Manchester M13 9PL. 5. Christie Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester M20 4BX.