title: Practical dosimetry methods for the determination of effective skin and breast dose for a modern CT system, incorporating partial irradiation and prospective cardiac gating.
abstract: OBJECTIVE
  For CT coronary angiography (CTCA), a generic chest conversion factor returns a significant underestimate of effective dose. The aim of this manuscript is to communicate new dosimetry methods to calculate weighted CT dose index (CTDIw), effective dose, entrance surface dose (ESD) and organ dose to the breast for prospectively gated CTCA.
  
  
  METHODS
  CTDIw in 32 cm diameter Perspex phantom was measured using an adapted technique, accounting for the segmented scan characteristic. Gafchromic XRCT film (International Speciality Products, New Jersey, NJ) was used to measure the distribution and magnitude of ESD. Breast dose was measured using high sensitivity metal oxide semiconductor field-effect transistors and compared to the computer based imaging performance assessment of CT scanners (ImPACT) dosimetry calculations.
  
  
  RESULTS
  For a typical cardiac scan the mean ESD remained broadly constant (7-9 mGy) when averaged over the circumference of the Perspex phantom. Typical absorbed dose to the breast with prospectively gated protocols was within the range 2-15 mGy. The subsequent lifetime attributable risk (LAR) of cancer incidence to the breast was found at 0.01-0.06 for a 20-year-old female. This compares favourably to 100 mGy (LAR ~0.43) for a retrospectively gated CTCA.
  
  
  CONCLUSIONS
  Care must be taken when considering radiation dosimetry associated with prospectively gated scanning for CTCA and a method has been conveyed to account for this. Breast doses for prospectively gated CTCA are an order of magnitude lower than retrospectively gated scans. Optimisation of cardiac protocols is expected to show further dose reduction.
authors: Department of Clinical and Radiation Physics, Directorate of Healthcare Science and Technology, Plymouth Hospitals NHS Trust, Plymouth, UK. robert.loader@nhs.net
authors: R J
authors: RJ
authors: Loader
authors: O
authors: O
authors: Gosling
authors: C
authors: C
authors: Roobottom
authors: G
authors: G
authors: Morgan-Hughes
authors: N
authors: N
authors: Rowles
mesh_terms: D001940:Breast / Q000528:radiation effects*; D017023:Coronary Angiography / Q000009:adverse effects* / Q000379:methods; D005260:Female; D006801:Humans; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods; D012307:Risk Factors; D012867:Skin / Q000187:drug effects*; D014057:Tomography, X-Ray Computed / Q000009:adverse effects*