Evaluation of two-dimensional bolus effect of immobilization/support devices on skin doses: A radiochromic EBT film dosimetry study in phantom
Side view of EBT film setup with alpha-cradle on a solid phantom. For the field, the SSD was 100 cm. For the IMRT field, the SSD was 93.6 cm.
Experimental EBT film images exposed to 6 MV photon fields, in size. The labels on the right indicated the open field (topmost) and the six support devices used during the film exposures.
Calibration curves for EBT films of lots #35076 (circle) and #36124 (square) with error bars.
(a) The cross-sectional RD profiles for open field and with the different devices, (b) the RD ratios along the central line with and without the support devices, and (c) and (d) the RD ratio variations in 3D view for the carbon fiber grid with Mylar sheet and perforated AquaPlast™ sheet, respectively.
DAH curves for 6 MV fields, open field (air interface) shown by the solid curve, and with six support devices shown by broken curves.
Visual images of EBT films irradiated by IMRT fields, (a) for 6 and (b) 15 MV at the air interface (left) and in the presence of alpha-cradle (right). The darker color represents high dose. The effective measurement depths of the upper and lower films were at 0.0153 and 0.0459 cm, respectively.
Color-wash isodose display extracted from the EBT film dosimetry for 6 MV IMRT field. Left: Film stack at air interface (without the alpha-cradle). Right: Film stack under alpha-cradle. The upper and lower graphs are for the upper and lower films, respectively. The dose enhancement in the presence of alpha-cradle was observed. The dose enhancement was more pronounced for the upper film (shallower depth).
DAH curves for 6 (left) and 15 MV (right) IMRT beams. The thick and thin curves are for alpha-cradle and air interface, respectively. The broken and solid curves are for the upper and lower films, respectively.
Fitting coefficients of the Rodbard function [Eq. (2)] for the calibration curves for EBT films of lots #35076 and #36124.
Values of DAH parameters [RD] at the air interface or in the presence of the immobilization/support devices for 6 MV photon beam, in field size. Also listed is the enhancement factor, defined as the ratio of the RD values with and without the support device for a given of total area evaluated.
Dose area histogram parameters, in unit of Gy and DAP values in Gy for 6 and 15 MV photon IMRT beams at the air interface or with alpha-cradle. Enhancement factor is defined as the ratio of or DAP values with and without alpha-cradle at a given film measurement depth.
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