Wilson Byron, Otto Karl, Gete Ermias
Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada.
Medical Physics, BC Cancer Agency, Vancouver, British Columbia, V5Z 4E6, Canada.
Med Phys. 2017 Jan;44(1):240-248. doi: 10.1002/mp.12036.
We present a Trajectory-based Volumetric Modulated Arc Therapy (TVMAT) technique for Stereotactic Radiosurgery (SRS) that takes advantage of a modern linacs ability to modulate dose rate and move the couch dynamically. In addition, we investigate the quality of the developed TVMAT method and the dosimetric accuracy of the technique.
The main feature of the TVMAT technique is a standard beam trajectory formed by dynamic motion of the treatment couch and the linac gantry. The couch rotates slowly through 180 degrees while the gantry delivers radiation through continuous sweeps of the gantry. The number of partial arcs that constitute the trajectory can be varied between two and eight and as the number of partial arcs increases, the trajectory more finely samples 4π geometry. Along these trajectories, the multi-leaf collimator (MLC) and dose rate are optimized through an inverse planning framework. The TVMAT method was tested on ten cranial SRS patients who were previously treated with the Dynamic Conformal Arc (DCA) technique. The plans were compared with the DCA and a four- arc VMAT technique with regards to dose to the OAR, dose falloff, V12Gy, and V4Gy. Validation measurements were performed using ion-chamber and Gafchromic film. In addition, the trajectory-log files were analyzed and compared with the treatment plan beam data.
The TVMAT treatment plans were successfully delivered with a treatment time between 3-8 min which mostly depended on total cumulated dose. Ion chamber measurements had an average measured error of 1.1 ± 0.6% and a maximum value of 2.2% of the delivered dose. The 2%, 2 mm gamma pass rates for the film measurements were 96% or greater. In a preliminary comparison of ten patients who underwent SRS treatments with the DCA technique, the TVMAT and VMAT techniques were able to produce plans with comparable dose falloff and OAR doses, while achieving better dose conformality, V4Gy and V12Gy when compared to the original DCA plans. The improvement of the TVMAT plans were as follows (mean % improvement ± standard err): Conformity (10 ± 2%), V4 (20 ± 20%), V12 (27 ± 10%), volume weighted mean dose to organs at risk (13 ± 13%), homogeneity index (2 ± 2%) and falloff (4 ± 2%).
We have developed and validated a trajectory-based dose delivery method which has dose distribution improvements while having a treatment time of 3-8 min. In addition, it has the potential for a simpler planning experience while maintaining an accurate delivery on the Varian Truebeam Linac.
我们提出一种基于轨迹的容积调强弧形治疗（TVMAT）技术用于立体定向放射外科治疗（SRS），该技术利用了现代直线加速器调制剂量率和动态移动治疗床的能力。此外，我们研究了所开发的TVMAT方法的质量以及该技术的剂量学准确性。
TVMAT技术的主要特点是由治疗床和直线加速器机架的动态运动形成的标准射束轨迹。治疗床缓慢旋转360度，而机架通过连续扫描机架来输送辐射。构成轨迹的部分弧形数量可在2至8之间变化，并且随着部分弧形数量的增加，轨迹对4π几何形状的采样更精细。沿着这些轨迹，通过逆向计划框架对多叶准直器（MLC）和剂量率进行优化。TVMAT方法在10例先前接受过动态适形弧形（DCA）技术治疗的颅脑SRS患者身上进行了测试。将这些计划与DCA计划以及四弧形容积调强弧形治疗（VMAT）技术在危及器官的剂量、剂量下降、V12Gy和V4Gy方面进行了比较。使用电离室和Gafchromic胶片进行了验证测量。此外，对轨迹日志文件进行了分析，并与治疗计划射束数据进行了比较。
TVMAT治疗计划成功实施，治疗时间在3至8分钟之间，这主要取决于总累积剂量。电离室测量的平均测量误差为1.1±0.6%，最大值为所输送剂量的2.2%。胶片测量的2%、2毫米伽马通过率为96%或更高。在对10例接受DCA技术SRS治疗的患者进行的初步比较中，TVMAT和VMAT技术能够产生剂量下降和危及器官剂量相当的计划，同时与原始DCA计划相比，在剂量适形性、V4Gy和V12Gy方面表现更好。TVMAT计划的改善情况如下（平均改善百分比±标准误差）：适形性（10±2%）、V4（20±20%）、V!2（27±10%）、危及器官的体积加权平均剂量（13±13%）、均匀性指数（2±2%）和剂量下降（4±2%）。
我们已经开发并验证了一种基于轨迹的剂量输送方法，该方法在剂量分布方面有所改善，同时治疗时间为3至8分钟。此外，它有可能提供更简单的计划体验，同时在瓦里安Truebeam直线加速器上保持准确的输送。
