Rankine Leith, Wan Hanlin, Parikh Parag, Maughan Nichole, Poulsen Per, DeWees Todd, Klein Eric, Santanam Lakshmi
Department of Radiation Oncology, Washington University School of Medicine, St. Louis, Missouri, USA.
Department of Oncology, Aarhus University Hospital, Aarhus, Denmark.
Int J Radiat Oncol Biol Phys. 2016 Jun 1;95(2):818-26. doi: 10.1016/j.ijrobp.2016.01.047. Epub 2016 Feb 2.
To demonstrate that fiducial tracking during pretreatment Cone-Beam CT (CBCT) can accurately measure tumor motion and that this method should be used to validate 4-dimensional CT (4DCT) margins before each treatment fraction.
For 31 patients with abdominal tumors and implanted fiducial markers, tumor motion was measured daily with CBCT and fluoroscopy for 202 treatment fractions. Fiducial tracking and maximum-likelihood algorithms extracted 3-dimensional fiducial trajectories from CBCT projections. The daily internal margin (IM) (ie, range of fiducial motion) was calculated for CBCT and fluoroscopy as the 5th-95th percentiles of displacement in each cardinal direction. The planning IM from simulation 4DCT (IM4DCT) was considered adequate when within ±1.2 mm (anterior-posterior, left-right) and ±3 mm (superior-inferior) of the daily measured IM. We validated CBCT fiducial tracking as an accurate predictive measure of intrafraction motion by comparing the daily measured IMCBCT with the daily IM measured by pretreatment fluoroscopy (IMpre-fluoro); these were compared with pre- and posttreatment fluoroscopy (IMfluoro) to identify those patients who could benefit from imaging during treatment.
Four-dimensional CT could not accurately predict intrafractional tumor motion for ≥80% of fractions in 94% (IMCBCT), 97% (IMpre-fluoro), and 100% (IMfluoro) of patients. The IMCBCT was significantly closer to IMpre-fluoro than IM4DCT (P<.01). For patients with median treatment time t < 7.5 minutes, IMCBCT was in agreement with IMfluoro for 93% of fractions (superior-inferior), compared with 63% for the t > 7.5 minutes group, demonstrating the need for patient-specific intratreatment imaging.
Tumor motion determined from 4DCT simulation does not accurately predict the daily motion observed on CBCT or fluoroscopy. Cone-beam CT could replace fluoroscopy for pretreatment verification of simulation IM4DCT, reducing patient setup time and imaging dose. Patients with treatment time t > 7.5 minutes could benefit from the addition of intratreatment imaging.
证明在治疗前锥形束CT（CBCT）期间进行基准点跟踪可准确测量肿瘤运动，并且该方法应用于在每个治疗分次前验证四维CT（4DCT）边界。
对于31例腹部肿瘤并植入基准标记物的患者，在202个治疗分次中，每天用CBCT和荧光透视法测量肿瘤运动。基准点跟踪和最大似然算法从CBCT投影中提取三维基准轨迹。计算CBCT和荧光透视法的每日内部边界（IM）（即基准点运动范围），作为每个基本方向上位移的第5至95百分位数。当模拟4DCT（IM4DCT）的计划IM在每日测量的IM的±1.2毫米（前后、左右）和±3毫米（上下）范围内时，认为是足够的。通过比较每日测量的IMCBCT与治疗前荧光透视法测量的每日IM（IMpre-fluoro），我们验证了CBCT基准点跟踪作为分次内运动的准确预测指标；将这些与治疗前和治疗后的荧光透视法（IMfluoro）进行比较，以确定那些可从治疗期间成像中受益的患者。
对于94%（IMCBCT）、97%（IMpre-fluoro）和100%（IMfluoro）的患者，四维CT无法准确预测≥80%分次的分次内肿瘤运动。IMCBCT比IM4DCT显著更接近IMpre-fluoro（P<0.01）。对于中位治疗时间t<7.5分钟的患者，IMCBCT在93%的分次（上下方向）上与IMfluoro一致，而t>7.5分钟组为63%，这表明需要针对患者的治疗期间成像。
从4DCT模拟确定的肿瘤运动不能准确预测在CBCT或荧光透视法上观察到的每日运动。锥形束CT可替代荧光透视法用于模拟IM4DCT的治疗前验证，减少患者摆位时间和成像剂量。治疗时间t>7.5分钟的患者可从增加治疗期间成像中受益。
