MR加速器在乳腺癌放疗中的临床应用

Preliminary application of MR-Linac in breast cancer radiotherapy in a single academic center

目的介绍MR加速器应用于乳腺癌术前放疗的应用流程和注意事项, 并报告不良反应。方法中国医学科学院肿瘤医院拟开展一项单臂、Ⅱ期临床研究, 入组患者实施MR加速器下术前瘤床补量, 2周内进行保乳手术, 术后6周内接受辅助全乳照射, 研究终点为≥2级急性不良反应。首例应用MR加速器术前放疗乳腺癌患者43岁, 为右乳外象限浸润性癌, cT_(2)N_(0)M_(0)期, AJCC第8版ⅡA期。患者接受CT和MR定位、MR指导下靶区勾画、Monaco系统计划设计, MR加速器下摆位并基于位移适应调整, 单次8 Gy照射。患者的剂量计算考虑了1.5 T磁场存在下的电子回旋效应(ERE)及电子束效应(ESE)。结果首例患者治疗顺利, 计划的正常器官满足限量要求, 因ERE及ESE导致的皮肤剂量增加幅度不大(D_(max) 8.44 Gy), 下颌及右上臂受量均很低(D_(max) 28.5、17.8 cGy), 无>1级急性不良反应。患者放疗后第7天接受保乳术, 未出现严重手术并发症, 伤口愈合及时。结论 1.5 T磁场对皮肤、下颌和手臂的剂量影响较小, 放疗及放疗后手术均无明显并发症增加。MR加速器下乳腺癌的放疗尚需更大样本的经验积累, 以不断优化治疗流程。

Objective To describe a prospective study of pre-operative tumor-bed boost performed at the 1.5 T MR-Linac in combination with adjuvant whole breast irradiation,and a first case,with an accentuation on clinical feasibility and safety.Methods A phase II,single arm study recruiting early stage patients follows a paradigm that first boosts the tumor bed and then undergoes breast conservative surgery in 2 weeks,and last irradiates the whole breast in 6 weeks.The primary endpoint is≥grade 2 acute breast toxicity.A 43 years old patient affected by a breast carcinoma,not special type of the right-sided lateral quadrant,staged cT_(2)N_(0)M_(0),was planned and treated.The dose,8 Gy for one time,was calculated by Monaco on CT simulation images.Both the air electron stream effect(ESE)and the electron return effect(ERE)at the presence of 1.5 T magnetic field were evaluated.During the pre-treatment evaluation,we carried out adaptation-to-position adjustment.Results The normal organ dosimetry is within toleration.The D_(max) to the skin,the chin and the right upper arm was 8.44 Gy,28.5 cGy and 17.8 cGy,respectively.There was no increased toxicity from ERE and ESE,and the treatment was well tolerated without>grade 1 acute toxicity.The patient received breast conservative surgery on day 7 without delayed wound healing.Conclusions This is the first case successfully treated within a clinical trial by pre-operative tumor-bed boost under 1.5 T MR-Linac in our institution.More participants are needed to validate and optimize the paradigm.