呼吸运动模式对胸部肿瘤SBRT剂量分布影响的研究

Effect of Respiratory Movement Patterns on Dose Distribution of SBRT in Thoracic Tumors

目的:研究呼吸运动的波形、幅度及肿瘤体积对胸部肿瘤立体定向放射治疗剂量分布的影响,为临床选取呼吸管理措施提供参考。方法:选取30例胸部肿瘤患者,用QUASAR^(TM)程控呼吸运动仪拖动二维矩阵PTW 1000SRS模拟肺部肿瘤在头脚方向运动,在不同呼吸信号(正弦波、呼吸训练后平稳信号、真实不规则信号)和呼吸幅度(0 mm、2mm、5mm、8mm、10mm)时采集等中心层面剂量分布,分析采集数据与放疗计划系统计算所得剂量分布差异,Pearson法分析γ通过率差值W_(ijk)与体积的相关性。结果:呼吸运动对胸部肿瘤立体定向体部放射治疗计划产生的剂量误差主要分布在靶区边缘剂量高梯度区,靶区边缘外侧为剂量热点,内侧为冷点,呼吸幅度为2mm时,不同呼吸模式下的平均γ通过率均>99%(99.17%±0.68%~99.40%±0.55%),差异<0.5%,W_(ijk)与体积呈弱负相关(r=-0.11,r=-0.19,r=-0.086,P>0.05);呼吸幅度为5mm时,平均γ通过率均>94%(94.64%±1.07%~96.30%±1.16%),W_(ijk)与体积大小呈中度负相关(r=-0.53,r=-0.55,r=-0.42,P<0.05);呼吸幅度为8mm时,平均γ通过率均<90%(85.23%±3.11%~86.95%±4.34%),不能满足临床需求,W_(ijk)与靶区体积中度负相关及强相关(r=-0.69,r=-0.59,r=-0.66,P<0.001);呼吸幅度10mm时,平均γ通过率均<80%(72.84%±5.10%~77.59%±5.33%),W_(ijk)与靶区体积强负相关(r=-0.79,r=-0.73,r=-0.75,P<0.001)。结论:呼吸运动模式对胸部肿瘤立体定向体部放射治疗技术(Stereotactic Body Radiation Therapy,SBRT)的影响由剂量模糊效应和肿瘤移动与多叶光栅运动之间的相互作用效应共同贡献,剂量热点多分布在靶区边缘外侧,冷点多分布在内侧。呼吸幅度较大(≥5mm)时,小体积肿瘤受呼吸运动模式的影响更显著,呼吸训练可改善呼吸波形,呼吸管理可减少呼吸幅度,平稳的呼吸模式能提高γ通过率,提升SBRT计划的精准度。

Objective:This study aims to investigate the effects of respiration waveform,respiration amplitude and tumor volume on dose distribution of stereotactic radiotherapy for thoracic tumors,and provide evidence for clinical of respiration management measures.Methods:30 patients with chest tumor were selected.2D matrix PTW 1000SRS was driven by the QUASAR program respiratory motometer to simulate the movements of lung tumors in the cranial-to-caudal direction.Dose distribution was recorded in different respiration signals(sinusoidal signals,stable signals after training,irregular signals)and respiration amplitudes(0 mm,2 mm,5 mm,8 mm,10 mm).The difference between the collected data and the dose distribution calculated by treatment planning system was analyzed.The correlations between γ pass rates and volumes were analyzed by the Pearson method.Results:The dose errors caused by respiratory movements on the stereotactic body radiation therapy(SBRT)plan were mainly distributed in high-dose planning tumor volume margins.The dose hot spots were in the outer edges of the target areas,while the dose cold spots were in the inner edges.When the respiration amplitude was 2 mm,the average y pass rates in different respiration signals were more than 99%(99.17%±0.68%~99.40%±0.55%);the difference among them was less than 0.5%;the correlation between W_(ijk) and volume was weakly negative(r=-0.11,r=-0.19,r=-0.086,P>0.05).When the respiration amplitude was 5 mm,the average 7 pass rales different respiration signals were more than 94%(94.64%±1.07%〜96.30%±1.16%);and the correlation between W_(ijk) and volume was moderately negative(r=-0.53,r=-0.55,r=-0.42,P<0.05).When the respiration amplitude was 8 mm,the average y pass rates different respiration signals were less than 90%(85.23%±3.11%〜86.95%±4.34%),which could not meet the clinical needs;the correlation between W_(ijk) and volume in stable signals was moderately negative(r=-0.59,P<0.001),and that in sinusoidal and irregular signals was strongly negative(r=-0.69,r=-0.66,P<0.001).When the respiration amplitude was 10 mm,the average γ pass rates in different respiration signals were less than 80%(72.84%±5.10%〜77.59%±5.33%),which could not meet the clinical needs;the correlation between W_(ijk) and volume was strongly negative(r=-0.79,r=-0.73,r=-0.75,P<0.001).Conclusion:The effect of respiratory movement patterns on SBRT for thoracic tumors was attributed to dose-effect ambiguity and the interaction between tumor movement and multi-leaf collimator movement.Dose hot spots were mostly distributed in the outer edge of target area,while cold spots were mostly distributed in the inner side.When the respiration amplitude is relatively large(≥5 mm),small tumors are more significantly affected by respiratory motion pattems.The waveform and amplitude of respiratory movements and the γ pass rate can be further improved by respiration training,respiration management and stable respiration pattern,respectively,enhancing the accuracy of SBRT plan.