Paul De Bruin PhD, Presenter: Nothing to Disclose

Koos Geleijns PhD, Abstract Co-Author: Nothing to Disclose

To facilitate dose assessment in pediatric CT for volumetric CT head and CT thorax scan protocols on a 320 detector row axial CT scanner by calculating equivalent organ doses using Monte Carlo simulations on 0, 1, 5, and 10 year old anthropomorphic mathematical phantoms (MIRD).

Measured spectra, geometric information (focus to axis of rotation distance, and position of the bow tie filters) and the design and composition of the bow tie filters were made available (Aquilion ONE, Toshiba, Japan). Scanner characteristics were implemented in an algorithm for Monte Carlo dose calculations (ImPACT MC, VAMP, Germany). For validation of the MC algorithm dose measurements were performed free-in-air and in CT phantoms. Equivalent organ dose was calculated in 4 anthropomorphic mathematical phantoms (MIRD, ages 0,1,5, and 10) for two clinically relevant acquisition configurations: head CT (120kV, small bow tie filter) and thorax CT (100kV, medium bow tie filter).

Measurements of dose profiles free-in-air and CTDI in phantoms showed good correspondence with the calculated values thus indicating appropriate modeling of the CT scanner characteristics in the Monte Carlo algorithm. For the pediatric CT head scan we calculated normalized equivalent dose to brain tissue of 0.80; 0.71; 0.62; and 0.59 mSv/mGy; and for thyroid of 0.40; 0.23; 0.10; and 0.05 mSv/mGy; respectively for 0, 1, 5 and 10 year old patients. For the pediatric CT thorax scan we calculated normalized equivalent dose to lung tissue of 0.85; 0.73; 0.63; and 0.49 mSv/mGy; and for breast tissue of 0.72; 0.65; 0.59; and 0.52 mSv/mGy; respectively for 0, 1, 5 and 10 year old patients. Equivalent organ doses (mSv) are normalized to absorbed dose free-in-air (mGy).

Axial head CT and thoracic CT of neonates and small children benefit from recent advances in volumetric cone beam technology, such as increased acquisition speed and consequently less motion artefacts. To adequately implement this new CT technology that is increasingly used in the clinic, instruments are required that provide accurate dose assessment. Our results show a significant trend of lower normalised equivalent organ dose at higher ages.

Accurate estimators of dose incurred by CT are needed for objective evaluation of CT scan justification. This abstract estimates paediatric organ doses incurred by two common CT protocols.

De Bruin, P, Geleijns, K, Assessment of Equivalent Organ Dose for a 320 Detector Row Volume CT Scanner Using Monte Carlo Simulations for Pediatric Head CT and Thorax CT for a Range of Ages.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8014953.html