ABSTRACT
Objective To measure the distortion of digital images generated by radiotherapy simula-tor,and to study the appropriate method of correction. Methods The grid correction plate and Microsoft Visual C + + 6.0 were used for correction. The area error and boundary maximum displacement error of dig-ital images before and after correction were calculated. The post-correction images were compared with film images to evaluate the correction method. Results The area error was 0.31% - 12.36%, and the bounda-ry displacement error was more than 0 -6 mm for 4 cm ×4 cm - 12 cm × 12 cm radiation field before correc-tion. For commonly used radiation field(12 cm × 12 cm) ,the post-correction area error and the boundary displacement error were 0.48% and 0.46 mm,respectively. Conclusions The least square and polynomi-al fitting correction method can fulfill the requirement of conventional radiotherapy.