Two dimensional (2D) anisotropy function of 57 Co is comparable to that of 192 Ir and its radial dose function has an increasing trend in some distances, which could lead to larger dose to deeper tissue [ 11 ]. 153 Gd radionuclide with average energy of 60.9 keV was proposed as a low dose rate or pulsed dose rate brachytherapy source [ 12 ].
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