Program Information
TG 51 Dosimetry : With Or Without Lead
M Shah*, A Meigooni , Comprehensive cancer center of Nevada - Las Vegas, NV
Presentations
SU-E-J-110 Sunday 3:00PM - 6:00PM Room: Exhibit HallTG-51 Dosimetry: With or Without Lead
Purpose: In this project, an analytical method has been introduced for adjustment of the TG-51 recommended KQ in order to produce accurate dosimetric data for high energy photons without the lead foil.
Methods: These investigations were performed using a 30 cm x 30 cm x 30 cm CIVCO water tank, A12 EXRADIN Water proof Farmer Chamber, a Standard Imaging MAX 4000 electrometer, and 1 mm thick lead foil from Standard Imaging. Complete TG-51 was performed every month with and without lead. The results were analyzed and an analytical model has been developed for comparing the values of KQ. TG-51 Table I was used to obtain KQ values.
Results: The dosimetric evaluations were obtained for Varian Linear accelerators Model 21ix and 21ex. These results indicates that the measured data with lead foil in place as recommended by TG-51 is in excellent agreement (within 0.1%) with the calculated data obtained by the new model, from our dosimetry data without-lead. If equation 15 of the TG-51 report is used without any adjustments, it will lead to differences of about 1.6 % (on the average) in relative data which will result in differences of about 0.3 % (on the average) in the KQ Values.
The KQ value for 18 MV obtained consistently with the equation of TG-51 “with lead†and “without lead“ were 0.971 and 0.974, respectively. The 0.3 % higher results for KQ without lead eventually will lead to 0.3% larger output. However, by considering this model the KQ value was found to be 0.971 for dosimetry without lead.
Conclusion: The analytical model that was introduced in this project was able to reproduce the dosimetric data of the high energy linear accelerators to within 0.1% without the use of the lead foil.
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