体膜固定宫颈癌55例放疗腹部皮下脂肪厚度与体积对摆位误差影响

Effect of thickness and volume of abdominal subcutaneous fat in 55 patients with cervical cancer treated by thermoplastic mask fixation on setup error

目的腹部皮下脂肪是影响宫颈癌放射治疗摆位的重要因素,影响着宫颈癌的放疗精度。本研究应用锥形束CT(cone beam CT,CBCT)探究腹部皮下脂肪厚度与体积对宫颈癌摆位误差的影响,对摆位工作和临床计划靶区体积(planning target volume,PTV)外扩范围提供建议。方法选取2016-01-01-2019-02-01南华大学第一附属医院55例宫颈癌患者为研究对象,对患者摆位固定,进行CT定位。治疗前应用首次CBCT扫描获取的图像,再与CT定位图像自动配准并手动微调,计算患者分别在x轴(左右方向)、y轴(头脚方向)、z轴(腹背方向)3个方向的摆位误差,并用治疗计划系统测量腹部皮下脂肪厚度及体积,并对厚度和体积分别分为3组。结果 55例患者在x、y、z轴3个方向的摆位误差分别为(0.62±2.96)、(0.89±3.25)和(0.71±1.50)mm。患者的皮下脂肪厚度和体积与y轴方向摆位误差的分析差异有统计学意义,P<0.05;在x、z轴方向与摆位误差的分析差异无统计学意义,P>0.05。在y轴方向上,皮下脂肪厚度及体积与脚方向组的分析差异有统计学意义,P<0.05。y轴方向摆位误差与皮下脂肪厚度和体积的大小关系分析中,平均厚度<10mm的摆位误差为(1.67±2.17)mm,10~20mm的摆位误差为(0.96±3.37)mm,>20mm的摆位误差为(2.43±4.34)mm。体积<300cm^3的摆位误差为(1.21±2.12)mm,300~500cm^3的摆位误差为(0.96±4.03)mm,>500cm^3的摆位误差为(1±4.11)mm。结论在55例宫颈癌患者的3个轴向中,y轴的摆位误差最大。y轴方向摆位误差与皮下脂肪厚度及体积增加趋势一致,因此需要更加关注平均厚度>20mm或体积>500cm^3患者在y方向的摆位情况,尤其是在脚方向的摆位。

OBJECTIVE Abdominal subcutaneous fat is an important factor affecting the positioning of cervical cancer radiotherapy,affecting its radiotherapy accuracy.This syudy was to investigate the effect of abdominal subcutaneous fat thickness and volume on cervical cancer setup errors by cone beam computed tomography(CBCT),and provide advice on positioning work and clinical planning target volume(PTV)expansion.METHODS The study was adopted to analyze 55 cervix cancer patients from the First Affiliated Hospital of University of South China,and the patients were placed in fixed positions for CT positioning.the first CBCT scan was used to obtain images before the treatment,which were then automatically registered with CT positioning images and fine-tuning manually.The setup errors of patients in xdirection(lateral),ydirection(longitudinal),zdirection(vertical)were calculated,and the thickness and volume of abdominal subcutaneous fat were measured by treat planning system.All the patients were respectively divided into three groups by the fat thickness and volume.RESULTS The setup errors of the 55 patients in the x,yand zdirections were(0.62±2.96)mm,(0.89±3.25)mm,(0.71±1.50)mm,respectively.Analysis of the patient’s subcutaneous fat thickness and volume and the setup error in the y-axis direction were statistically significant(P>0.05).In the y-axis direction,the analysis of the thickness and volume of subcutaneous fat and the direction of the foot group was statistically significant(P<0.05).The setup errors in the thickness groups which were devided into<10 mm,10-20 mm and>20 mm were(1.67±2.17)mm,(0.96±3.37)mm and(2.43±4.34)mm,respectively.The setup errors in the volume groups which were devided into<300 cm^3,300-500 cm^3,>500 cm^3 were(1.21±2.12)mm,(0.96±4.03)mm and(1±4.11)mm,respectively.CONCLUSIONS Among the three directions,the ydirection setup error is the largest in the55 cervical cancer patients.The positioning error in the y-axis direction are consistent with the increase of the thickness and volume of subcutaneous fat.Therefore,more attention needs to be paid to the positioning in the y-direction for patients with an average thickness> 20 mm or a volume> 500 cm^3,especially in the foot direction.