胃癌术后容积旋转调强放疗计划设计中肠道空腔的应对策略

Strategic study of the design in volumetric modulated arc therapy plan for gastric cancer patients with large gastrointestinal pneumatosis

目的探讨胃癌术后容积旋转调强放疗(VMAT)计划设计中肠道空腔的应对策略。方法选取2018-08-01-2019-08-01空军军医大学第一附属医院放疗科定位前经胃肠道准备后靶区周围肠道仍有大量气体的胃癌患者10例。将定位CT图像(命名为CT-initial)上的空腔全部勾画出来,拷贝4套图像,分别将空腔的CT值赋予-500、-400、-300和40,并将这4套图像分别命名为CT-HU(-500)、CT-HU(-400)、CT-HU(-300)和CT-HU(40),其中CT-HU(40)为模拟空腔完全消失下的状态。使用美国瓦里安公司Eclipse 13.5计划系统为所有患者分别在5套图像上设计VMAT计划Plan-HU(initial)、Plan-HU(-500)、Plan-HU(-400)、Plan-HU(-300)和Plan-HU(40),将5个计划分别移植到CT-initial和CT-HU(40)图像上,评估靶区V_(95%)、V_(100%)、D_(98%)、D_(50%)、D_(2%)和危及器官受量。结果Plan-HU(initial)、Plan-HU(-500)、Plan-HU(-400)移植到CT-HU(40)图像上,V_(95%)明显下降,靶区明显欠剂量。Plan-HU(40)移植到CT-initial图像上,D_(2%)明显增大,剂量-体积直方图上靶区的梯度明显变差。Plan-HU(-300)移植到CT-initial和CT-HU(40)图像上,V_(95%)均能达到临床要求,虽然在CT-initial上D_(2%)略有增加,但是在CT-HU(40)上明显提高了V_(100%)。患者2和患者5因为空腔体积超大(>50%靶体积),V_(100%)相对较差。所有计划危及器官受量差异无统计学意义。结论患者空腔体积<50%靶体积时,将空腔HU设置为-300,设计出的VMAT计划无论在原图还是空腔完全填充的2个极端状态下,各项参数都能满足临床要求;患者空腔≥50%靶体积时,剂量分布无法满足临床要求,建议采取相应措施后再行放疗。

Objective To establish and evaluate volumetric modulated arc therapy(VMAT) plan design strategies for patients with pneumatosis and find out the optimal design strategy to minimize pneumatosis interference.Methods Totally ten gastric cancer cases with gastrointestinal pneumatosis treated in Department of Radiation Oncology of First Affiliated Hospital of Air Force Medical University from August 1 st, 2018 to August 1 st, 2019 were used for plan design and evaluation.All pneumatosis areas were contoured in original CT images(CT-initial) and their CT values were manually assigned to-500,-400,-300 and 40,replicating other four mimic images.These mimic images were named as CT-HU(-500),CT-HU(-400),CT-HU(-300) and CT-HU(40) respectively.CT-HU(40) image mimicked the situation that no pneumatosis existed.VMAT plans were designed in Varian Eclipse 13.5 system on the five images(initial and mimic images) mentioned above and created five treatment plans: Plan-HU(initial),Plan-HU(-500),Plan-HU(-400),Plan-HU(-300) and Plan-HU(40).These plans were then transplanted back to CT-initial and CT-HU(40) images and doses were re-calculated.V_(95%),V_(100%),D_(98%),D_(50%) and D_(2%) for PTVs and doses at OARs were evaluated and compared.Results V_(95%) was dramatically decreased when plan-HU(initial),plan-HU(-500) and plan-HU(-400) were transplanted onto CT-HU(40) images, indicating a prominent under dose in PTV.D_(2%) distinctly increased and target dose gradient was enlarged when Plan-HU(40) was transplanted onto CT-initial.V_(95%) could meet the clinical requirements when Plan-HU(-300) was transplanted both onto CT-initial and CT-HU(40).Under such circumstance, although D_(2%) was slightlyincreasing on CT-initial,V_(100%) notably increased on CT-HU(40).V_(100%) results were relatively unsatisfactory in Patient No.2 and No.5.This was because too large pneumatosis volume(greater than 50% of PTV)affected the calculations.There was no statistic difference at doses at OARs between different plans.Conclusions When pneumatosis volume is less than 50% of PTV,VMAT plans,with pneumatosis CT values setting to-300,can meet clinical requirements under both pneumatosis existing and vanishing conditions.However,when pneumatosis volume is greater than 50% of PTV,VMAT plan designs can not meet clinical dose distribution requirements.Physical exhaustion to reduce pneumatosis volume should be needed.