This Article Abstract Full Text Full Text (PDF) Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Avilés Lucas, P Articles by Vañó Carruana, E Search for Related Content PubMed PubMed Citation Articles by Avilés Lucas, P Articles by Vañó Carruana, E

Analysis of surface dose variation in CT procedures

¹Physics Department, The Royal Marsden NHS Trust, Fulham Road, London SW3 6JJ, UK and ²Departamento de Radiología, Facultad de Medicina, Universidad Complutense de Madrid, Madrid 28040, Spain

View larger version (17K): [in a new window]   Figure 1. Configuration used to measure or calculate the air kerma–length product on the surface of an elliptical phantom (for clarity, the figure is not drawn to scale). The chamber is placed on the upper phantom surface. The horizontal and vertical axes of the tomographic plane are given by x and y, whereas z refers to the rotation axis. R is the distance between the focus and the isocentre, is the projection angle, is the angle between the chamber–focus and the focus–isocentre vectors, r is the distance between the focus and the centre of the chamber and h is distance of the ionisation chamber from the isocentre.

View larger version (12K): [in a new window]   Figure 2. Two schematic free-in-air kerma profiles parallel to the axis of rotation of the CT scanner (z-axis), shown at distance rcos from the focus, at the isocentre. When rectangular collimation is used, the shapes of the two profiles are simply related using similar triangles once the inverse-square law dependence is explicitly stated in accordance with Equation (5). The distances rcos and R are shown in Figure 1.

View larger version (11K): [in a new window]   Figure 3. Surface air kerma–length product (AKLP) as a function of the offset of the phantom centre along the vertical y-axis of the tomographic plane. , measurements with phantom A; •, measurements with phantom B.

View larger version (10K): [in a new window]   Figure 4. Normalized surface air kerma–length product (AKLP) as a function of the chamber position along the y-axis. Results are normalized to the maximum surface AKLP measured for phantom A at the point closest to the isocentre (the latter being the origin). , measurements with phantom A; •, measurements with phantom B.

View larger version (10K): [in a new window]   Figure 5. Normalized air kerma–length product (AKLP) on the surface of phantom A as a function of the chamber position along the y-axis. Results are normalized to the value measured at the isocentre (origin of the coordinate system). , measurements with the large bow tie filter; •, measurements without the bow tie filter.

View larger version (13K): [in a new window]   Figure 6. Normalized air kerma–length product (AKLP) on the surface of elliptical phantoms A, B and C. ,measurements with the tube current modulation technique; •, measurements without the tube current modulation technique.

View larger version (12K): [in a new window]   Figure 7. Normalized air kerma–length product (AKLP) calculated on the surface of phantom B as a function of the chamber position along the y-axis. For each filter, results are normalized to the maximum AKLP. , calculations with large bow tie filter; , calculations with the small bow tie filter.