The absorbed dose of a target material can be determined by using the optical properties of poly(methyl methacrylate) (PMMA) irradiated with a high energy radiation. The concerns about radiation application reserach have increased in recent years. However, it seems that many researchers do not fully understand the prospects of an absorbed dose as a measurand of a radiation-induced energy absorption in a target material. This study was originally designed to obtain the calibration curves of PMMA dosimeters which have been parctically used in commercial gamma-ray irradiation facilities by introducing a method for evaluating an absorbed does with optical changes. When considering the range of an absorbed dose, the function of the calibration curve is simply determined from a fourth order polynomial.