Introduction:  On  the  basis  of  percent  depth  dose  (PDD)  calculation,  the  application  of  dosimetry  in  radiotherapy  has  an  important  role  to  play  in  reducing  the  chance  of  tumor  recurrence. The aim of this study is to introduce a new formula for calculating the centeral axis  percent depth doses of Cobalt-60 beam.   Materials and Methods: In the present study, based on ...