乳腺癌调强放疗患者体型特征与摆位固定精度的关系

Relationship between patient’s body shape characteristics and setup errors in intensity-modulated radiotherapy for breast cancer

目的分析保留乳房术后接受放疗的乳腺癌患者乳腺体积大小、身体质量指数(BMI)以及胸廓横纵轴比值(简称横纵比)与摆位误差之间的关系,为不同体型特征患者在计划靶区个性化外放边界设计时提供参考。方法选取2020-11-05-2021-05-21在中山大学肿瘤防治中心进行调强放疗的乳腺癌患者34例。所有患者使用发泡胶垫进行体位固定,运用瓦里安Vital Beam机载锥形束CT(CBCT)进行治疗前图像扫描,并获取头脚(SI)、左右(LR)、前后(AP)平移误差和冠状位(Rtn)、矢状位(Pitch)、横断位(Roll)旋转误差,分别与患者的乳腺体积大小、BMI以及胸廓横纵比进行Spearman相关性分析。应用公式[计划靶区外扩边界(M_(PTV))=2.5Σ+0.7σ]分别算出不同乳腺体积大小、BMI以及胸廓横纵比患者对应的M_(PTV)。结果患者乳腺体积与SI(r=0.159,P=0.024)以及AP(r=0.141,P=0.044)摆位误差呈正相关关系;BMI与AP误差呈正相关关系,r=0.162,P=0.021;胸廓横纵比与LR误差呈正相关关系,r=0.247,P<0.001。以中位数进行分组,大小乳腺体积组对应的M_(PTV)分别为:LR_(大)=8.87 mm,LR_(小)=6.37 mm;SI_(大)=9.90 mm,SI_(小)=5.42 mm;AP_(大)=7.38 mm,AP_(小)=8.62 mm。大小BMI组对应的M_(PTV)分别为:LR_(大)=8.71 mm,LR_(小)=6.72 mm;SI_(大)=9.42 mm,SI_(小)=6.59 mm;AP_(大)=8.65 mm,AP_(小)=7.30 mm。大小横纵比组对应的M_(PTV)分别为:LR_(大)=8.56 mm,LR_(小)=6.21 mm;SI_(大)=8.67 mm,SI_(小)=7.58 mm;AP_(大)=8.36 mm,AP_(小)=7.74 mm。结论在保留乳房术的乳腺癌患者放疗中,乳腺腺体体积、BMI以及胸廓横纵比与放疗摆位误差之间的存在相关关系。不同体型特征患者在放疗计划设计时应区分靶区外扩边界。

Objective To analyze the correlation between patient’s body shape characteristics,including breast volume,body mass index(BMI),the ratio of the horizontal and vertical axis in thorax(the aspect ratio)and the setup errors in patients with breast cancer who received radiotherapy after breast-conserving surgery,and to provide a reference for individualized margins of planning target volume(PTV).Methods Thirty-four breast cancer patients who underwent intensity-modulated radiotherapy(IMRT)in our hospital from November 5,2020 to May 21,2021 were selected.All patients used polyurethane foam sealing agent for immobilization.CBCT was given in Varian Vital Beam before radiotherapy to access the errors of head-foot(SI),left-right(LR),front-back(AP)and coronal(Rtn),sagittal(Pitch),and transverse(Roll)rotations.All the information was analyzed by Pearson’s correlation with the patient’s breast volume,BMI,and the aspect ratio.The formula(M_(PTV)=2.5Σ+0.7σ)was used to calculate the margin of the planning target volume(M_(PTV))for corresponding patients with different breast volume,BMI,and the aspect ratio.Results The patient’s breast volume was positively correlated with the setup errors of SI(r=0.159,P=0.024)and AP(r=0.141,P=0.044);BMI was positively correlated with AP(r=0.162,P=0.021)setup errors;The aspect ratio was positively correlated with LR(r=0.247,P<0.001)setup errors.Grouped by the median,the M_(PTV)corresponding to the large and small breast volume groups were LR_(lar)=8.87mm,SI_(lar)=9.90mm,AP_(lar)=7.38mm;LR_(sma)=6.37mm,SI_(sma)=5.42mm,AP_(sma)=8.62mm,The M_(PTV)of the large and small BMI groups were LR_(lar)=8.71 mm,SI_(lar)=9.42 mm,AP_(lar)=8.65 mm;LR_(sma)=6.72 mm,SI_(sma)=6.59 mm,AP_(sma)=7.30mm.The M_(PTV)of the large and small aspect ratio groups were LR_(lar)=8.56mm,SI_(lar)=8.67mm,AP_(lar)=8.36mm;LR_(sma)=6.21mm,SI_(sma)=7.58mm,AP_(sma)=7.74mm.Conclusion There is a correlation between patient’s body shape characteristics(breast volume,BMI,and the aspect ratio)and setup errors in radiotherapy for patients with breast cancer after breast-conserving surgery.Patients with different body shape characteristics should distinguish the M_(PTV).