摘要目的:分析磁共振加速器放疗计划中心点位置对偏中心肿瘤计划剂量学的影响。方法:回顾性选取2020年在中山大学肿瘤防治中心接受放疗的19例偏中心肿瘤病例资料，每个病例分别设计两组放疗计划：①按照磁共振加速器常规计划设计流程将计划等中心点固定设计调强放疗计划(A组)。②以靶区几何中心点作为治疗计划中心点设计调强放疗计划(B组)。比较两组放疗计划中靶区适形指数和均匀性指数、正常组织剂量和计划MU数。结果:两组治疗计划均能满足临床剂量要求。A和B组计划靶区适形指数和均匀性指数差异均无统计学意义( P>0.05)，正常组织受照剂量也无明显差别( P>0.05)。但是，A组计划MU数(1 149±903)明显高于B组(970±652)，差异有统计学意义( t＝2.804， P＝0.012)。 结论:虽然磁共振加速器计划等中心点位置固定，但计划质量可满足临床要求，开展磁共振加速器治疗偏中心肿瘤是可行的。

abstractsObjective:To analyze the dosimetric effects on off-center tumour treatment plan resulting from the MR-Linac-based isocenter position radiotherapy plan.Methods:The cases of 19 patients who were treated in Sun Yat-sen University Cancer Center in 2020 were collected in this study. Two different IMRT plans were designed for each patient with off-center tumor both for group A with planned isocenter position as IMRT and group B with planed target center position as geometric center. The conformity index and homogeneity index of target, the dose normal tissue and the number of MU were compared between two plans.Results:The two IMRT plans met clinical dosimetric requirements. No statistical differences were found both in homogeneity index and conformity index ( P>0.05). Also there was no differences found in doses to normal tissues. However, the MU number (1 149±903, t=2.804, P=0.012) in group A was higher than that in group B (970±652). Conclusions:It is feasible to perform MR-Linac-based off-center treatment plan.