Purpose:To explore the effects of changes in the gross tumor volume(GTV)on dose distribution in organs at risk(OARs)and healthy brain tissue in patients with gliomas.Methods:Eleven patients suffering from gliomas with IMRT plans treated with a simultaneous integrated boost technique planned before therapy(initial plans)were prospectively recruited.At the end of radiotherapy,patients underwent repeat computed tomography and magnetic resonance imaging,and IMRT was re-planned.The GTV and dosimetric parameters between the initial and re-planned IMRT were compared using the two-related-sample two-tailedWilcoxon test; correlations between the initial GTV and the re-planned target volumes were assessed using the bivariate correlation test.Results:The volume of the residual tumor didnot change significantly(P>0.05),the volume of the surgical cavity decreased significantly(P<0.05),and the GTV and target volumes decreased significantly at the end of IMRT(allP<0.05).The Dose near-max(D2%)to OARs and volumes of healthy brain tissue receiving total doses of 10-50Gy were lower in the IMRT re-plan than in the initial IMRT plan(all P<0.05).The GTV in the initial plan was significantly positively correlated with the changes in the GTV and planning target volume 1that occurred duringIMRT(all P<0.05).Conclusions:The reduction in the GTVin patients with gliomas resulted from shrinkage of the surgical cavity during IMRT,leading to increased doses to the OARs and healthy brain tissue.Such changes appeared to be most meaningful in patients with large initial GTV values.