Haertl Petra Maria, Loeschel Rainer, Repp Natalia, Pohl Fabian, Koelbl Oliver, Dobler Barbara
Radiat Oncol. 2013 Jun 25;8:153. doi: 10.1186/1748-717X-8-153.
The purpose of this study was to evaluate the impact of Cone Beam CT (CBCT) based setup correction on total dose distributions in fractionated frameless stereotactic radiation therapy of intracranial lesions.
Ten patients with intracranial lesions treated with 30 Gy in 6 fractions were included in this study. Treatment planning was performed with Oncentra® for a SynergyS® (Elekta Ltd, Crawley, UK) linear accelerator with XVI® Cone Beam CT, and HexaPOD™ couch top. Patients were immobilized by thermoplastic masks (BrainLab, Reuther). After initial patient setup with respect to lasers, a CBCT study was acquired and registered to the planning CT (PL-CT) study. Patient positioning was corrected according to the correction values (translational, rotational) calculated by the XVI® system. Afterwards a second CBCT study was acquired and registered to the PL-CT to confirm the accuracy of the corrections. An in-house developed software was used for rigid transformation of the PL-CT to the CBCT geometry, and dose calculations for each fraction were performed on the transformed CT. The total dose distribution was achieved by back-transformation and summation of the dose distributions of each fraction. Dose distributions based on PL-CT, CBCT (laser set-up), and final CBCT were compared to assess the influence of setup inaccuracies.
The mean displacement vector, calculated over all treatments, was reduced from (4.3 ± 1.3) mm for laser based setup to (0.5 ± 0.2) mm if CBCT corrections were applied. The mean rotational errors around the medial-lateral, superior-inferior, anterior-posterior axis were reduced from (-0.1 ± 1.4)°, (0.1 ± 1.2)° and (-0.2 ± 1.0)°, to (0.04 ± 0.4)°, (0.01 ± 0.4)° and (0.02 ± 0.3)°. As a consequence the mean deviation between planned and delivered dose in the planning target volume (PTV) could be reduced from 12.3% to 0.4% for D95 and from 5.9% to 0.1% for D(av). Maximum deviation was reduced from 31.8% to 0.8% for D95, and from 20.4% to 0.1% for D(av).
Real dose distributions differ substantially from planned dose distributions, if setup is performed according to lasers only. Thermoplasic masks combined with a daily CBCT enabled a sufficient accuracy in dose distribution.
本研究的目的是评估在颅内病变的分次无框架立体定向放射治疗中，基于锥形束CT（CBCT）的摆位校正对总剂量分布的影响。
本研究纳入了10例接受6分次、每次30 Gy治疗的颅内病变患者。使用Oncentra®软件，针对配备XVI®锥形束CT和HexaPOD™治疗床的SynergyS®直线加速器（英国克劳利的医科达有限公司）进行治疗计划。患者通过热塑性面罩（BrainLab，Reuther）固定。在根据激光进行初始患者摆位后，采集CBCT图像并与计划CT（PL-CT）图像配准。根据XVI®系统计算出的校正值（平移、旋转）对患者体位进行校正。之后，再次采集CBCT图像并与PL-CT配准，以确认校正的准确性。使用自行开发的软件将PL-CT进行刚体变换至CBCT几何结构，并在变换后的CT上进行各分次的剂量计算。通过反向变换和各分次剂量分布的求和得到总剂量分布。比较基于PL-CT、CBCT（激光摆位）和最终CBCT的剂量分布，以评估摆位不准确的影响。
在所有治疗中计算得到的平均位移向量，从基于激光摆位时的（4.3±1.3）mm降至应用CBCT校正后的（0.5±0.2）mm。在内侧-外侧、 superior-inferior、前后轴周围的平均旋转误差，从（-0.1±1.4）°、（0.1±1.2）°和（-0.2±1.0）°，降至（0.04±0.4）°、（0.01±0.4）°和（0.02±0.3）°。因此，计划靶区（PTV）中计划剂量与实际 delivered剂量之间的平均偏差，对于D95可从12.3%降至0.4%，对于D(av)可从5.9%降至0.1%。D95的最大偏差从31.8%降至0.8%，D(av)的最大偏差从20.4%降至0.1%。
如果仅根据激光进行摆位，实际剂量分布与计划剂量分布有很大差异。热塑性面罩结合每日CBCT可实现足够的剂量分布准确性。
