胸中上段食管癌锥形束CT两处参考点标记位置摆位误差研究

Setup errors by CBCT with selecting two different reference point marking positions for super and middle part of esophageal carcinoma in chest

目的参考点标记方法是肿瘤CT模拟定位标记的常用方法,食管癌调强放疗中选取不同参考点标记位置对摆位误差存在一定的影响。本研究应用锥形束CT(cone-beam CT,CBCT)研究胸中上段食管癌2处参考点标记位置的摆位误差。方法选取20例2016-01-01-2016-10-31于山东大学附属山东省肿瘤医院首次接受胸中上段食管癌调强放射治疗(intensitymodulated radiation therapy,IMRT)患者。所有治疗次数分为奇数次和偶数次2组,参考点选在下颌骨体中线位置为下颌组;参考点选在胸骨剑突上方平坦处为胸部组。照射前摆位后获取CBCT在线匹配,得出左右、腹背和头脚方向摆位误差,并用2.5Σ+0.7δ算出计划靶区(planning target volume,PTV)外放界值。2组摆位误差比较行配对t检验。结果下颌组患者左右、腹背和头脚方向摆位误差分别为(0.34±1.55)、(1.22±1.65)和(-0.17±2.30)mm,胸部组的分别为(-0.50±2.40)、(-0.77±3.82)和(1.23±2.09)mm,2组在上述方向的比较P值分别为0.263、0.042和0.044。下颌组PTV外放界值分别为5.21、5.63和7.02 mm;胸部组PTV外放界值分别为7.20、11.94和7.87mm。结论采用下颌部位参考点标记的定位方法,在减少摆位误差方面优于胸部参考点标记定位方法。

OBJECTIVE Reference point marking method is the commonly used in CT simulation position marking method for tumor,and selecting different reference points have a certain influence of set-up errors,our study is to contrast analyze the set-up errors with selecting two different reference point by CBCT for super and middle part of esophageal cancer. METHODS From 2016-01-01 to 2016-10-31,20 patients with super and middle part of esophageal cancer accepted frist time intensity-modulated radiotherapy （IMRT） in Shandong Cancer Hospital Affiliated to Shandong University were chosen. All the treatments were divided into odd times group and even times group, marking reference points on the body midline of mandible was the mandible group- marking reference points on the flat above the xiphoid was the Thorax group, CBCT scan and auto-match online were regularly performed before the treatment, and the setup of Left-Right （LR）, Anterior-Posterior（AP） and Superior-Inferior（SI） were received. The value of the Mptv was calculated. The paired- samples t-test of was carried out between these two methods. RESULTS The shift errors in LR,AP and SI dimension of the mandible group were （0.83±2.27） ram,（-0.63±3.44） mm and （0.58±3.18） ram. The MPTV were 5.96 mm, 8.78 mm and 8.20 mm. The translation set-up errors in LR, AP and SI dimension of the Thorax group were （0. 67± 2.40） ram,（-2. 55 ± 5. 08） mm and （1. 15 ± 4. 01） mm, respectively. The MPTV were 6. 28 mm, 12. 69 mm and 10. 19 mm,respectively. The T-test results were P=0. 201,0. 000 and 0. 024. CONCLUSIONS The method with marking reference points on the body midline of mandible would be better than the one with marking reference points on the flat above the xiphoid in reducing the setup errors.