3 March 2012Significance of including field non-uniformities such as the heel effect and beam scatter in the determination of the skin dose distribution during interventional fluoroscopic procedures
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The current version of the real-time skin-dose-tracking system (DTS) we have developed assumes the exposure is
contained within the collimated beam and is uniform except for inverse-square variation. This study investigates
the significance of factors that contribute to beam non-uniformity such as the heel effect and backscatter from the
patient to areas of the skin inside and outside the collimated beam. Dose-calibrated Gafchromic film (XR-RV3,
ISP) was placed in the beam in the plane of the patient table at a position 15 cm tube-side of isocenter on a
Toshiba Infinix C-Arm system. Separate exposures were made with the film in contact with a block of 20-cm
solid water providing backscatter and with the film suspended in air without backscatter, both with and without
the table in the beam. The film was scanned to obtain dose profiles and comparison of the profiles for the various
conditions allowed a determination of field non-uniformity and backscatter contribution. With the solid-water
phantom and with the collimator opened completely for the 20-cm mode, the dose profile decreased by about
40% on the anode side of the field. Backscatter falloff at the beam edge was about 10% from the center and
extra-beam backscatter decreased slowly with distance from the field, being about 3% of the beam maximum
at 6 cm from the edge. Determination of the magnitude of these factors will allow them to be included in the
skin-dose-distribution calculation and should provide a more accurate determination of peak-skin dose for the
DTS.
Vijay Rana,Kamaljit Gill,Stephen Rudin, andDaniel R. Bednarek
"Significance of including field non-uniformities such as the heel effect and beam scatter in the determination of the skin dose distribution during interventional fluoroscopic procedures", Proc. SPIE 8313, Medical Imaging 2012: Physics of Medical Imaging, 83131N (3 March 2012); https://doi.org/10.1117/12.911528
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Vijay Rana, Kamaljit Gill, Stephen Rudin, Daniel R. Bednarek, "Significance of including field non-uniformities such as the heel effect and beam scatter in the determination of the skin dose distribution during interventional fluoroscopic procedures," Proc. SPIE 8313, Medical Imaging 2012: Physics of Medical Imaging, 83131N (3 March 2012); https://doi.org/10.1117/12.911528