鼻咽癌放疗中红外定位系统与锥形束CT的摆位精度比较

Comparison of optical positioning system and cone-beam computed tomography on positioning accuracy in radiotherapy for nasopharyngeal carcinoma

目的:量化研究鼻咽癌放射治疗过程中红外定位系统OPS与锥形束CT(CBCT)摆位精度的差异。方法:随机选取南通市肿瘤医院2018年4月~11月收治的鼻咽癌患者21例,使用头颈肩热塑膜固定体位,CT扫描前,在热塑膜上粘贴OPS专用定位球6个。首次治疗时使用千伏级CBCT进行位置验证,并移床校正,记录CBCT移床值和移床后的OPS监测偏差值。选择CBCT肿瘤中心摆位值作为理想放疗摆位参考,对室内激光定位系统的肿瘤中心摆位值和OPS肿瘤中心摆位值进行比较和分析。当摆位误差在2.0 mm内,则被认定与CBCT摆位临床一致。结果:与室内激光定位系统摆位相比,OPS大大提高了鼻咽癌放疗摆位的精度。OPS与CBCT在鼻咽癌放疗摆位一致性结果为:患者左右方向(用x轴表示)95.2%、腹背方向(用y轴表示)71.4%、头脚方向(用z轴表示)100.0%。腹背偏差较大主要是因为放射治疗计划系统选择颈椎骨作为参考点,此时选择CBCT摆位将无法消除颈椎骨弯曲产生的偏差。结论:OPS实现了在鼻咽癌放疗中实时、准确和快速的患者摆位,代替室内激光定位系统大大提高了鼻咽癌放疗摆位精度。在鼻咽癌放疗摆位精度方面,OPS和CBCT表现出较高的一致性,而且在每次放疗中均可使用。

Objective To quantitatively study the differences in positioning accuracy between optical positioning system(OPS)and cone-beam computed tomography(CBCT)in the radiotherapy for nasopharyngeal carcinoma.Methods Twenty-one patients with nasopharyngeal carcinoma who were admitted to Nantong Cancer Hospital were enrolled in the study.All the patients were immobilized with thermoplastic head-and-shoulder mask.Before CT scan,6 OPS infrared positioning balls were affixed to the mask.kV-CBCT scan was performed to validate the positioning errors before the first treatment,and the couch was then shifted according to the CBCT validation results.The couch shift when using CBCT and the deviations detected by OPS after couch shift were recorded.The positioning results of the room laser system and those of OPS were recorded,and then compared with those of CBCT which were taken as the reference.When the positioning errors were no more than 2.0 mm,OPS was considered consistent with CBCT in positioning.Results Compared with the room laser system,OPS remarkably improved the positioning accuracy of nasopharyngeal carcinoma radiotherapy.The consistencies between OPS and CBCT were 95.2%,71.4%and 100.0%in leftright,anterior-posterior and superior-inferior directions,respectively.The error caused by the bending of the cervical vertebrae when the cervical vertebrae was taken as the reference point in treatment planning system couldn't be avoided in positioning using CBCT,which led to a large deviation between CBCT and OPS in anterior-posterior direction.Conclusion OPS which achieves real-time,accurate and rapid patient positioning can replace the room laser system to greatly improve the positioning accuracy in nasopharyngeal carcinoma radiotherapy.OPS also has a high consistency with CBCT in positioning in nasopharyngeal carcinoma radiotherapy.Moreover,OPS can be used in all fractions.