头颈部肿瘤螺旋断层调强放疗摆位误差和计划靶区分析

Analysis of set-up error and PTV delineation for head and neck cancer treated with TomoTherapy

目的分析螺旋断层调强放疗系统治疗头颈部肿瘤时MVCT引导下的治疗摆位误差,探讨计划靶区外放范围。方法对25例头颈部肿瘤患者放疗行597次MVCT扫描,通过对MVCT图像与KVCT扫描图像进行自动匹配和手动调节,记录三维方向上的摆位误差值,并对记录数据进行统计学分析,计算临床靶体积(CTV)到计划靶体积(PTV)的外放边界。结果X、Y、Z轴移动均数分别为(-0.89±1.85)、(0.76±1.91)、(0.20±1.40)mm、旋转方向上平均误差为(0.26±0.91)°。结论治疗前通过MVCT扫描,获得分次间照射摆位误差并对其加以纠正,能够提高头颈部肿瘤放疗精度,PTV-CTV外放范围X、Y、Z各方向外放5 mm能够使处方剂量包绕98%的CTV体积,保证肿瘤区域的放疗剂量准确性和对正常组织的充分保护。

Objective To analyze the setup error of head-neck cancers treated with MVCT image-guided TomoTherapy system and explore PTV-CTV margin. Methods Twenty-five patients were treated with TomoTherapy and 597 times of MVCT imaging were scanned. We registered the reeongtructed MVCT image and planning KVCT, recorded the setup errors in three dimensions and ana- lyzed the data, and studied the PTV-CTV margins. Results Twenty-five patients were scanned by MVCT 597 times, and the mean movement values in X, Y and Z axis were （ 0.89 ± 1.85 ） , （0.76 ± 1.91 ） and （0.20 ± 1.40） ram, respectively. Setup error in roll direction was （0.26 ± 0.91 ） degree. Conclusion MVCT were implemented before treatment. Inter-fractional setup error a- nalysis and verification can improve the accuracy of treatment for head-neck cancer. A 5mm margin expansion in X, Y and Z axis was e- nough to make prescription dose cover 98% CTV volume and guarantee the precise radiation dose and protect the normal tissue.