ABSTRACT
Objective: A correction factor was proposed to improve the accuracy of dose calculation in conventional radiotherapy when filed matching technique was used. Methods:Use the linear accelerator with independent collimator to implement semi-field irradiation under different equivalent-length field. Measure the dose and compare it with the calculation dose. Obtain a correction factor which change follow the equivalent-length through data fitting. Results:There is relationship to indicate the correction factor increase if the field area enlarge;the calculation dose will be close to the measure dose, and the accuracy will improve by correcting;Conclusion:The clinical dose of semi-field irradiation can be calculated by an equivalent square field technique , and then multiplied by the correction factor. it is a simple method to improve the accuracy of dose calculation in conventional radiotherapy by using semi-filed correction factor when filed matching technique was used.