MLC叶片厚度对颅内SRS逆向IMRT计划的影响评价

Dosimetric effects of multileaf collimator leaf width on inverse intensity-modulated radiotherapy in intracranial stereotactic radiosurgery

目的比较微型MLC （2 mm叶片厚度）和普通MLC （10 mm叶片厚度）在颅内SRS逆向IMRT计划中的剂量分布差异。方法鉴于微型MLC开野小的特点，选取30例颅内最大直径〈10 cm肿瘤进行比较，分别使用常规和微型MLC进行剂量学对比，保持所有计划优化参数一致，得到满足临床要求的逆向动态调强计划，T检验比较两种MLC条件下放疗计划中靶区和OAR受量。结果微型MLC和普通MLC相比，在靶区剂量分布方面前者优于后者（P＝0.019），但D98、D95、D50、D3相近（P＝0.774、0.650、0.170、0.080），而前者HI均值比后者低58.7%（P＝0.000），CI均值比后者高20.1%（P＝0.044）；OAR受量前者均小于后者，其中脑干Dmean、Dmax均值前者均低于后者，分别为10.0%、8.2%（P＝0.768、0.753），右眼和左眼Dmean、Dmax均值前者低于后者，依次为16.5%、19.3%和21.4%、13.4%（P＝0.572、0.775和0.734、0.630），左晶状体、右晶状体、左视神经、右视神经、视交叉Dmax均值前者均低于后者，依次为50.4%、24.1%、38.5%、27.8%、5.7%（P＝0.172、0.467、0.521、0.740、0.899）；正常组织PRV100、PRV50、PRV25前者体积均≤后者（P＝0.839、0.832、0.972）。结论微型MLC在颅内SRS逆向IMRT计划中优于普通MLC，其提高了靶区适形性，降低了OAR受量。

To compare the dosimetric effects of micro-multileaf collimator （MLC）（2 mm leaf width） and conventional MLC （10 mm leaf width） on inverse intensity-modulated radiotherapy （IMRT） in intracranial stereotactic radiosurgery （SRS）. Methods In view of the fact that the micro-MLC has a small open field, 30 patients with intracranial tumor with a〈10 cm diameter were enrolled in this study. Their inverse dynamic IMRT plans were established using conventional MLC （conventional group） and micro-MLC （micro group） with the same other conditions. The radiation doses to the target volume and the organs at risk （OAR） were compared between the two groups with t test.ResultsCompared with the conventional group, the micro group had a significantly better dose distribution in the target volume （P=0.019）. However, there were no significant differences in D98, D95, D50, and D3 between the two groups （P=0.774, 0.650, 0.170, 0.080）. The micro group had a 58.7% lower mean homogeneity index and a 20.1% higher mean conformity index than the conventional group （P=0.000）. The micro group had significantly lower radiation doses to OAR than the conventional group （P=0.044）. The mean Dmean and Dmax of the brain stem in the micro group were 10.0% and 8.2%, respectively, lower than those in the conventional group （P=0.768, 0.753）. The mean Dmean and Dmax of the right eye and left eye in the micro group were 16.5%, 19.3%, 21.4%, and 13.4%, respectively, lower than those in the conventional group （P=0.572, 0.775 and 0.734, 0.630）. The mean Dmax of the left lens, right lens, left optic nerve, right optic nerve, and optic chiasm in the micro group were 50.4%, 24.1%, 38.5%, 27.8%, and 5.7%, respectively, lower than those in the conventional group （P=0.172, 0.467, 0.521, 0.740, 0.899）. The PRV100, PRV50, and PRV25 of the normal tissue in the micro group were no more than those in the conventional group （P=0.839, 0.832, 0.972）.Conclusions In inverse IMRT in intracranial SRS, micro-MLC is better than conventional MLC because it can improve CI of the target volume and reduce the radiation doses to OAR.