背景:评估了在使用互补表面引导放射治疗(SGRT)和锥形束计算机断层扫描(CBCT)设置的左侧全乳房照射中,设置不确定性和组织变形的剂量学效应。
方法:通过计算变形CT图像上的剂量,模拟了29例患者的15个部分的40.05Gy处方剂量的疗程,基于每日CBCT图像,并将剂量变形并累积到计划CT图像上。临床目标体积(CTV)位置和形状的变异性评估为计划CTV和变形CTV结构之间的95%Hausdorff距离(HD95)。使用两种治疗技术在计划和模拟的累积剂量分布之间评估DVH指标:切向体积调制电弧疗法(tVMAT)和常规3D适形放射治疗(3D-CRT)。
结果:根据HD95值,使用互补的CBCT和SGRT设置,在85%的治疗级分中,5mmCTV-PTV边缘包围了CTV形状和位置的变化.在初始SGRT设置和CBCT设置之间观察到8.6mm的残余误差。使用tVMAT的CTVV95%覆盖率中位数为98.1%(范围93.1-99.8%),使用CBCT设置的3D-CRT技术的覆盖率为98.2%(范围84.5-99.7%)。使用初始的仅SGRT设置,相应的覆盖率为96.3%(范围92.6-99.4%)和96.6%(范围84.2-99.4%),分别。然而,观察到初始SGRT设置和CBCT设置之间的垂直残余误差存在相当大的偏差.未观察到计划剂量和累积剂量对危险器官(OAR)的临床相关变化。
结论:即使每天设置CBCT,CTV到PTV的边缘也不应减少到5毫米以下。tVMAT和3D-CRT技术在靶和OAR的剂量覆盖方面都是稳健的。基于设置方法之间的转变,建议使用CBCT设置作为SGRT的补充方法。
BACKGROUND: The dosimetric effect of setup uncertainty and tissue deformations in left-sided whole-breast irradiation with complementary surface-guided radiotherapy (SGRT) and cone-beam computed tomography (CBCT) setup was evaluated.
METHODS: Treatment courses of 40.05 Gy prescribed dose in 15 fractions were simulated for 29 patients by calculating the dose on deformed CT images, that were based on daily CBCT images, and deforming and accumulating the dose onto the planning CT image. Variability in clinical target volume (CTV) position and shape was assessed as the 95% Hausdorff distance (HD95) between the planning CTV and deformed CTV structures. DVH metrics were evaluated between the planned and simulated cumulative dose distributions using two treatment techniques: tangential volumetric modulated arc therapy (tVMAT) and conventional 3D-conformal radiotherapy (3D-CRT).
RESULTS: Based on the HD95 values, the variations in CTV shape and position were enclosed by the 5 mm CTV-PTV margin in 85% of treatment fractions using complementary CBCT and SGRT setup. A residual error of 8.6 mm was observed between the initial SGRT setup and CBCT setup. The median CTV V95% coverage was 98.1% (range 93.1-99.8%) with tVMAT and 98.2% (range 84.5-99.7%) with 3D-CRT techniques with CBCT setup. With the initial SGRT-only setup, the corresponding coverages were 96.3% (range 92.6-99.4%) and 96.6% (range 84.2-99.4%), respectively. However, a considerable bias in vertical residual error between initial SGRT setup and CBCT setup was observed. Clinically relevant changes between the planned and cumulative doses to organs-at-risk (OARs) were not observed.
CONCLUSIONS: The CTV-to-PTV margin should not be reduced below 5 mm even with daily CBCT setup. Both tVMAT and 3D-CRT techniques were robust in terms of dose coverage to the target and OARs. Based on the shifts between setup methods, CBCT setup is recommended as a complementary method with SGRT.