Institute of Clinical Research, University of Southern Denmark, Odense DK-5000, Denmark.
Med Phys. 2011 Aug;38(8):4802-10. doi: 10.1118/1.3615621.
Elekta accelerators controlled by the current clinically used accelerator control system, Desktop 7.01 (D7), uses binned variable dose rate (BVDR) for volumetric modulated arc therapy (VMAT). The next version of the treatment control system (Integrity) supports continuously variable dose rate (CVDR) as well as BVDR. Using CVDR opposed to BVDR for VMAT has the potential of reducing the treatment time but may lead to lower dosimetric accuracy due to faster moving accelerator parts. Using D7 and a test version of Integrity, differences in ability to control the accelerator, treatment efficiency, and dosimetric accuracy between the two systems were investigated.
Single parameter tests were designed to expose differences in the way the two systems control the movements of the accelerator. In these tests, either the jaws, multi leaf collimators (MLCs), or gantry moved at constant speed while the dose rate was changed in discrete steps. The positional errors of the moving component and dose rate were recorded using the control systems with a sampling frequency of 4 Hz. The clinical applicability of Integrity was tested using 15 clinically used VMAT plans (5 prostate, 5 H&N, and 5 lung) generated by the SmartArc algorithm in PINNACLE. The treatment time was measured from beam-on to beam-off and the accuracy of the dose delivery was assessed by comparing DELTA4 measurements and PINNACLE calculated doses using gamma evaluation.
The single parameter tests showed that Integrity had an improved feedback between gantry motion and dose rate at the slight expense of MLC control compared to D7. The single parameter test did not reveal any significant differences in the control of either jaws or backup jaws between the two systems. These differences in gantry and MLC control together with the use of CVDR gives a smoother Integrity VMAT delivery compared to D7 with less abrupt changes in accelerator motion. Gamma evaluation (2% of 2 Gy and 2 mm) of the calculated doses and DELTA4 measured doses corrected for systematic errors showed an average pass rate of more than 97.8% for both D7, Integrity BVDR, and Integrity CVDR deliveries. Direct comparisons between the measured doses using strict gamma criteria of 0.5% and 0.5 mm showed excellent agreement between D7 and Integrity delivered doses with average pass rates above 95.7%. Finally, the Integrity control system resulted in a significant 35% (55 +/- 13 s) reduction in treatment time, on average.
Single parameter tests showed that the two control systems differed in their feedbac loops between MLC, gantry, and dose rate. These differences made the VMAT deliveries more smooth using the new Integrity treatment control system, compared to the current Desktop 7.01. Together with the use of CVDR, which results in less abrupt changes in dose rate, this further increases the smoothness of the delivery. The use of CVDR for VMAT with the Integrity desktop results in a significant reduction in treatment time compared to BVDR with an average reduction of 35%. This decrease in delivery time was achieved without compromising the dosimetric accuracy.
目前临床使用的 Elekta 加速器控制设备 Desktop 7.01（D7）在容积调强弧形治疗（VMAT）中使用了分段变量剂量率（BVDR）。下一代治疗控制系统（Integrity）支持连续变量剂量率（CVDR）和 BVDR。与使用 BVDR 相比，使用 CVDR 进行 VMAT 治疗有降低治疗时间的潜力，但由于加速器部件移动速度更快，可能会导致剂量学准确性降低。使用 D7 和 Integrity 的测试版本，研究了这两种系统在控制加速器、治疗效率和剂量学准确性方面的差异。
设计了单参数测试来暴露两种系统控制加速器运动方式的差异。在这些测试中，当剂量率以离散步长改变时，要么是机架、多叶准直器（MLC）或龙门架以恒速移动。使用控制系统以 4 Hz 的采样频率记录移动部件的位置误差和剂量率。使用 PINNACLE 中的 SmartArc 算法生成的 15 个临床使用的 VMAT 计划（5 个前列腺、5 个头颈部和 5 个肺部）来测试 Integrity 的临床适用性。从束流开启到束流关闭测量治疗时间，并通过 DELTA4 测量和使用伽马评估比较 PINNACLE 计算剂量来评估剂量输送的准确性。
单参数测试表明，与 D7 相比，Integrity 在轻微影响 MLC 控制的情况下，在龙门架运动和剂量率之间具有更好的反馈。两种系统之间的单参数测试未显示在机架或备用机架控制方面存在任何显著差异。这些在龙门架和 MLC 控制方面的差异以及 CVDR 的使用，与 D7 相比，为 Integrity VMAT 输送提供了更平滑的输送，加速器运动的变化不那么突然。使用 2%的 2 Gy 和 2 mm 伽马评估（2%的 2 Gy 和 2 mm）计算剂量和 DELTA4 测量剂量，并校正系统误差，显示 D7、Integrity BVDR 和 Integrity CVDR 输送的平均通过率均超过 97.8%。直接使用严格的 0.5%和 0.5 mm 伽马标准比较测量剂量，显示 D7 和 Integrity 输送剂量之间具有极好的一致性，平均通过率均超过 95.7%。最后，Integrity 控制系统平均减少了 35%（55 +/- 13 s）的治疗时间。
单参数测试表明，两种控制系统在 MLC、龙门架和剂量率之间的反馈回路存在差异。这些差异使新的 Integrity 治疗控制系统在进行 VMAT 输送时更加平滑，与目前的 Desktop 7.01 相比。结合 CVDR 的使用，这导致剂量率的变化不那么突然，这进一步提高了输送的平滑度。与使用 D7 的 BVDR 相比，使用 Integrity 台式机的 CVDR 进行 VMAT 治疗可显著减少治疗时间，平均减少 35%。在不影响剂量学准确性的情况下实现了输送时间的缩短。
