Abstract: Objective To compare the dose distribution of SIBIMRT and SBCRT in the radiotherapy of brain metastasis. Methods Eleven patients with multiple brain metastasis tumors were sketched the target areas of metastasis and whole brain through CT simulative localization. Plans of SIB and CRT were made by Varian Eclips system. The whole brain PTV was 40Gy／20f， and the metastasis PGTV was 60Gy／20f in SIB plan. In CRT plan the whole brain PTV was 40Gy／20f， then the metastasis PGTV was an extra boost of 20Gy／10f. The maximum and mean dose of the whole brain， brain stem， optic nerves and lens were compared using a matched pair study. Also we compared the comformity index（CI） and heterogeneity index（HI） of the PGTV.
ResultsThe mean dose of the left and right optic nerves， the whole brain and the brain stem were 35.2±5.2，38.9±5.5，41.9±3.7 and 44.6±4.2Gy in SIB plan， and were 40.7±8.9，42.6±6.4，47.8±7.6 and 49.2±5.3Gy in CRT plan. The maximum dose of these organs were 42.3±3.5，43.6±3.2，46.6±4.1and 55.5±4.7Gy in SIB plan， and were 45.6±3.5，47.3±4.7，50.4±3.6 and 64.3±6.6Gy in CRT plan. The mean and the maximum dose in the SIB plan were less than those in the CRT plan with siginificant differents. The dose of the lens seemed to be no difference in the two plans. The CI of PGTV in the SIB plan was 0.88±0.07, which was significantly superior to 072±011 in the CRT plan. The HI of PGTV in the SIB plan was 1.06±0.02, which is significantly lower than 1.09±0.03 in the CRT plan. The difference of CI and HI was statistically significant. Conclusion On the condition that the wholebrain and the brain metastasis tumor receive the same amount of physical dose， rather than SB-CRT， the SIB-IMRT may more efficiently reduce the dose acting on normal tissues of brain， improve the CI and HI of PTV，and theologically improve the therapeutic effect， reduce the acute and tardus damage caused by radiotherapy.