Calculation of effective dose from measurements of secondary neutron spectra and scattered photon dose from dynamic MLC IMRT for , , and beam energies
The foil Bonner system used to measure the neutron spectra: (a) Set of Bonner spheres, (b) Au-foil holder inside the Bonner sphere, and (c) Close-up of Au-foil holder and orientation of Au activation foil.
Comparison of the known spectrum and the unfolded data from measurements with the foil Bonner Sphere system. Measurements were made for a source at Georgia Institute of Technology NNRC calibration facility.
The setup for in-field measurements at isocenter with Bonner sphere.
The setup for out-of-field measurements at superior to isocenter with Bonner sphere.
The unfolded neutron spectra for and conventional and IMRT delivered at isocenter and measured at isocenter and superior to isocenter.
Details of center location of each organ: Distance from isocenter along the longitudinal axis to center of organ and depth from phantom surface to center of organ. These data were determined using measurement tools in Eclipse and from measurements of estimated organ locations in the ART phantom.
Summary of the and conventional (conv) and IMRT neutron ambient dose equivalents, and neutron fluences, , average photoneutron energy, measured at isocenter (iso) and superior to isocenter (40).
Neutron fluences per MU measured at isocenter and superior to isocenter (iso) are compared to neutron fluences per MU reported in the literature.
Neutron component of organ equivalent dose in Sv per unit photon Gy delivered to isocenter. Ambient dose equivalents measured at isocenter were applied to organs in close proximity to the treatment volume (bladder, colon, gonads, and bone marrow). Ambient dose equivalents measured superior to isocenter were applied to all other organs. The neutron component of equivalent dose for each organ was then approximated by correcting the ambient dose equivalents for the depth of each organ by applying neutron depth dose data from d’Errico et al. (Ref. 12).
X-ray component of organ equivalent dose in Sv per unit photon Gy delivered to isocenter.
Comparison of peripheral x-ray doses measured in this study to peripheral x-ray doses reported in the literature for , , and . X-ray doses are compared for the following organ locations: Liver, stomach, lung, esophagus, and thyroid. All data are in units of per MU delivered.
Organ equivalent doses (shaded in light grey) in units of Sv per unit photon Gy delivered to isocenter were calculated by summing the neutron and x-ray components of equivalent dose for each organ. The effective doses (shaded in dark grey) were calculated, for each beam energy, by summing the product of equivalent dose and the appropriate tissue weighting factor for all organs.
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