肿瘤调强放射治疗中子宫活动度

Uterine mobility in intensity modulated radiation therapy

目的:通过统计研究15名手术前宫颈癌病人的调强放射治疗技术(IMRT)治疗过程中的子宫活动度,为制定放疗计划中更准确的计划靶区(PTV)。同时使得在使用锥形束CT(Cone-Beam CT,CBCT)以及图像配准过程中,更好地确定治疗位置以确保剂量的准确性。方法:通过Philips16排CT获取病人治疗前的模拟定位CT图像,CMS(XIO)计划系统完成宫颈癌IMRT放射治疗计划,传送定位CT图像至Elekta Synergy的XVI系统。选取15名手术前宫颈癌病例。在放射治疗前获取CBCT图像,通过XVI系统进行3D图像配准,获取治疗中摆位误差(60组数据),子宫位移(60组数据),计算获取治疗中病人子宫活动度数据(60组数据)。子宫活动度为通过摆位误差和子宫位移计算后得到的绝对值差值数据。整个研究获得180组研究数据,每组数据分别包含3个方向:Left-Right(LR),Anterior Posterior(AP),InferiorSuperior(IS),以及3个方向的旋转角度。本文研究子宫在各个方向上的活动度,确定治疗计划制定时,PTV的确定不仅包括了系统误差数据,同时结合了治疗时的随机误差数据。结果:子宫活动度为:系统误差(Σ)LR、IS、AP的数值为0.15cm、0.22 cm、0.41 cm;随机误差(δ)LR、IS、AP的数值为0.11 cm、0.11 cm、0.15 cm。子宫内膜癌与宫颈癌摆位误差数据为:系统误差(Σ)LR、IS、AP的数值为0.18 cm、0.23 cm、0.29 cm;随机误差(δ)LR、IS、AP的数值为0.08 cm、0.05 cm、0.07cm。通过DVH和靶区覆盖可能性分析指出,PTV的间隙为摆位误差与子宫活动度误差的总和。计算得到PTV为:LR=0.67 cm,IS=0.88 cm,AP=1.37 cm。结论:研究子宫活动度对于在肿瘤放射治疗中,治疗的随机误差与系统误差分析具有指导作用。指导物理师对PTV外放的合理性,有效降低正常组织受量与靶区剂量的充足。

Objective To determine a more accurate planning target volume （PTV） in the intensity modulated radiation therapy （IMRT） plan by statistically researching on the uterine mobility of 15 preoperative patients with cervical cancer during the IMRT, which can also determine the treatment location and ensure the accuracy of the dose during the application of Cone Beam CT （CBCT） and image registration. Methods Patients＇ CT simulated localization images were obtained by Philips 16 row CT. And CMS （X10） planning system was applied to complete the IMRT plan, and transmit CT localization images to XVI system of Elekta Synergy. The 15 preoperative patients with cervical cancer were randomly selected. The CBCT images before the radiation therapy were obtained and then conducted the three-dimensional image registration by XVI system to get position errors, uterine displacements during the treatment, with 60 sets of data of each. By calculating, 60 sets of uterine mobility data during the treatment were also obtained. Uterine mobility was the difference between the absolute values calculated by position errors and uterine displacement. In the whole research, 180 sets of data were obtained and each sets of data respectively contained three directions： Right-Left （RL）, Anterior Posterior （AP）, Superior-lnferior （SI） and rotation angle with three directions. The uterine mobility at all directions was researched to determine a better IMPT plan, and the determination of PTV involved the system errors and the random errors during the treatment. Results For uterine mobility, the LR, IS, AP with consideration of system errors （∑） were 0.15 cm, 0.22 cm, 0.41 cm respectively, while the LR, IS, AP with consideration of random errors （8） were 0.11 cm, 0.11 cm, 0.15 cm respectively. For treatment position errors of endometrial cancer and cervical cancer, LR, IS, AP with consideration of system errors （∑） were 0.18 cm, 0.23 cm, 0.29 cm respectively, while the LR, IS, AP with consideration of random errors （5） were 0.08 cm, 0.05 cm, 0.07 cm respectively. By DVH and target coverage probability analysis, the gap of PTV was the sum of position errors and uterine mobility errors. And after calculation, the PTV in this research was LR=0.67 cm, IS=0.88 cm, AP=1.37 cm. Conclusion The analysis of random and system errors during the treatment provides the guidance for the research on uterine mobility during the IMRT, and guides the physicists to determine the proper margin of PTV, effectively reducing the normal tissues dose and ensuring the target volume doses.