New gamma evaluation algorithm was created to improve ability of gamma criterion to determine, whenever field – in field plan two dose distributions are acceptable for further therapy. New parameter, dose gradient, was introduced to differentiate high dose gradient regions from low and use only those with high dose gradient. The aim of this article is to determine whether the new gamma criterion algorithm evaluation principle is suitable for FIF plans verification. For this study a 17 x 12 cm rectangular 6MV photon beam was used. Rectangular fields, sized 5 x 12, 6 x 8,5 and 3 x 4,3 cm were added as segments for each 17 x 12 cm base field in center. Dose distribution was calculated using treatment-planning system (TPS) to be used as a starting point to make distorted plans with segments displaced in superior, inferior, lateral left and lateral right directions to simulate patient movement or positioning errors during irradiation. Dose distributions for the distorted plans were measured using pixel ionization chambers detector array. The resulting dose distributions were compared to the reference one provided by TPS using gamma criterion. For acceptance criteria DM=3% dose-difference, dM=3 mm distance-to-agreement (DTA) and dose gradient 5% were used and 95% of all pixels should be within this criterion. For all the plans, considered in the present paper, 95% threshold was exceeded before the displacement reached clinically significant values of 3 mm. New algorithm show steep decrease of ―pass‖ pixels at 3 mm even for segments with 3 x 4, 3 cm size. One has to conclude, that created algorithm should be investigated at comparison of dose distribution plans of clinical field in field conformal radiotherapy.