The neutron dose equivalent evaluation and shielding at the maze entrance of a Varian Clinac 23EX treatment room
Scheme of the vault for the semiempirical calculations. The distance is from the isocenter C to the point A on the maze centerline from which the isocenter is just visible. The distance is from the point A to the outside of the maze door (point B). The inner maze entrance cross-sectional area and the cross-sectional area along the maze are denoted by and , respectively. When the gantry angle is 270°, the beam is directed from point D toward point E.
Scheme of the point of measurement in this study. The letters from a to l represent the possible BPE board locations in the maze. The locations d–i are where the BPE boards were finally installed. Points A–E are the same to those in Fig. 1. When the gantry angle is 270°, the gantry head is close to the west wall and the beam is directed from point D toward point E.
The measured and with different gantry angles and jaw settings. The closed and open fields correspond to a field size of and , respectively. Both units of the and the were converted to dose equivalent rate .
Comparison of the measured dose equivalent and the calculation results at the maze entrance of the Varian Clinac 23EX accelerator. The measurement results and the calculation to measurement ratios were shown with uncertainties (in parenthesis).
Final measurements at the maze entrance and the control area of adjacent vault.
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