螺旋断层MVCT在鼻咽癌自适应放射治疗中的剂量学研究

Dosimetric study of TOMO-MVCT in ART of nasopharyngeal carcinoma

目的:研究螺旋断层放射治疗系统(TOMO)兆伏级CT(MVCT)成像(TOMO-MVCT)在鼻咽癌自适应放射治疗(ART)中直接用于剂量计算的可行性。方法:采用数表法随机选取20例行鼻咽癌TOMO治疗的患者,采集患者首次治疗的MVCT图像,在TOMO治疗计划系统中,将采集到的MVCT图像与放射治疗计划的千伏级CT(kVCT)图像进行融合配准。将治疗计划植入MVCT图像中,选取相应MVCT电子密度曲线进行剂量计算。比较分析基于MVCT和kVCT图像计算的靶区和危及器官(OAR)剂量分布差异。结果:MVCT相对于kVCT图像计算的肿瘤靶区(GTV)和计划靶区(PTV)剂量D95分布相对误差分别为(0.65±0.58)%和(0.66±0.73)%;OAR脑干、脊髓、左晶体、右晶体、左眼球、右眼球、左视神经、右视神经和垂体剂量Dmax分别为(0.70±1.16)%、(0.31±2.26)%、(-0.19±1.32)%、(-0.33±1.96)%、(-0.15±2.34)%、(0.37±1.32)%、(0.40±0.72)%、(0.29±0.55)%和(0.53±0.70)%;左腮腺和右腮腺的D50分别为(0.65±1.11)%和(0.26±0.86)%。结论:基于TOMO-MVCT成像与kVCT图像的剂量计算差异<2%。TOMO-MVCT图像可直接用于鼻咽癌ART的剂量计算。

Objective:To investigate the feasibility of direct application of tomotherapy megavoltage computed tomography(TOMO-MVCT)in dose calculation of adaptive radiation therapy(ART)of nasopharyngeal carcinoma.Methods:Twenty patients with nasopharyngeal carcinoma who underwent the treatment of TOMO were randomly selected by number table method.The MVCT images of patients who received the first treatment were collected.In the TOMO treatment planning system,the MVCT images were fused and mated with the kilovoltage CT(kVCT)images of radiotherapy plan.The treatment plan was implanted into the MVCT image,and the MVCT electron density curve was selected to implement dose calculation.The differences of dose distribution of target volume and organ at risk(OAR)based on the calculations of MVCT and kVCT images were compared and analyzed respectively.Results:The relative error of D95 of gross tumor volume(GTV)and planning target volume(PTV)between MVCT and KVCT image were(0.65±0.58)%and(0.66±0.73)%,respectively.The relative errors of Dmax of OARs,included brain stem,spinal cord,left lens,right lens,left eyeball,right eyeball,left optic nerve,right optic nerve and pituitary,between MVCT and kVCT image was(0.70±1.16)%,(0.31±2.26)%,(-0.19±1.32)%,(-0.33±1.96)%,(-0.15±2.34)%,(0.37±1.32)%,(0.40±0.72)%,(0.29±0.55)%,(0.53±0.70)%,respectively.The relative errors of D50 of left parotid and right parotid between MVCT and KVCT image were(0.65±1.11)%and(0.26±0.86)%,respectively.Conclusion:The difference of dose calculation based on TOMO-MVCT and kVCT images is less than 2%.The TOMO-MVCT images can be directly applied in dose calculation of adaptive radiation therapy of nasopharyngeal carcinoma.