he JARP protocol for the determ i nation of absorbed dose from higyenergy X-ray and electron beams was applied to the dose plotting system (DPS), which consists of a water phantom, a scaning mechanism of the ionization chamber (PTWN23323), and a computor system. Since a shape of this PTW chamber is different from the JARP chamber, absorbed dose conversion factors, Cλ and CE, were calculated for this chamber. Cλ values of this chamber considerably agree with those of the JARP chamber, but CE values of this chamber do not. Therefore, to accord to the JARP protocol, the present DPS should be improved as follows: For the determination of dose distribution from a high enrgy electron beam, firstly, a mean incident energy of an electron beam is determined using measurement data of a central axis depth-ionization curve. Secondly, a central axis depthdose curve is obtained, taking into consideration of above calculated CE values. Finaly, dose distributions off central axis are estimated on the following assumption. If a chamber reading at an off -axial point is the same as that at an axial point, an absorbed dose at a given off - axial point is assumed to be the same as the corresponding axial dose.

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