Purpose:To compare dosimetry difference in the whole central nervous system(CNS)radiotherapy in both intensity-modulated radiation therapy(IMRT)and three dimensional conformal radiation therapy(3D-CRT).Methods:In allusion to 38 patients with the whole CNS radiotherapy,IMRT and 3D-CRT plans were separately designed.Under the precondition of guaranteeing two plans all meet the clinical requirements,to compare target dose distribution,conformal index(CI)and homogeneity index(HI),exposure doses of both organs at risk(OARs)and normal tissues outside of target,monitor units(MU)and treatment time,respectively,and to investigate the dosimetry difference.Results:Compared with 3D-CRT plan,V5 and average dose Dmean of lung for IMRT plan increased markedly,and the difference was statistically significant(P < 0.05),whereas V20 was rather lower(P < 0.05),V10 change was not obvious(P>0.05); radiation dose,V10 and V20 of heart significantly decreased(P < 0.05)while radiation dose and volume of kidney remarkably increased(P < 0.05); V5 and D50 of liver were relatively higher(P < 0.05),moreover,V15 and V20 decreased notably(P < 0.05),but V10 change was not obvious(P>0.05); maximum dose of crystalline lens had no statistical difference(P>0.05); eye maximum dose was prominently lower(P < 0.05).Conclusions:IMRT plan is more capable of distinctly improving the dosimetric index of target and immensely reducing the high dose radiation volume of normal tissues and OARs than 3D-CRT plan,furthermore,IMRT plan can better enhance HI(P=0.67)and CI(P=0.00)of the target dose distribution,also,ameliorate problems of both dose distribution inhomogeneity and dose "hot" or "cold" spots existed in 3D-CRT plan.High dose volume above 50%prescription dose of normal tissues significantly decreases in IMRT plan,the dosimetric indices of OARs are mixed,although both plans can meet the clinical requirements,IMRT plan has an advantage over 3D-CRT plan in clinical dosimetry.