PURPOSE To investigate the potential benefit of multileaf collimator (MLC) tracking guided by kilovoltage intrafraction monitoring (KIM) during stereotactic body radiotherapy (SBRT) in the liver, and to understand trends of target overdose with MLC tracking. METHODS Six liver SBRT patients with 2-3 implanted gold markers received SBRT delivered with volumetric modulated arc therapy (VMAT) in three fractions using daily cone-beam CT setup. The CTV-to-PTV margins were 5 mm in the axial plane and 10 mm in the cranio-caudal directions, and the plans were designed to give minimum target doses of 95% (CTV) and 67% (PTV). The three-dimensional marker trajectory estimated by post-treatment analysis of kV fluoroscopy images acquired throughout treatment delivery was assumed to represent the tumor motion. MLC tracking guided by real-time KIM was simulated. The reduction in CTV D95 (minimum dose to 95% of the clinical target volume) relative to the planned D95 (ΔD95) was compared between actual non-tracking and simulated MLC tracking treatments. RESULTS MLC tracking maintained a high CTV dose coverage for all 18 fractions with ΔD95 (mean: 0.2 percentage points (pp), range: -1.7 to 1.9 pp) being significantly lower than for the actual non-tracking treatments (mean: 6.3 pp range: 0.6-16.0 pp) (p = 0.002). MLC tracking of large target motion perpendicular to the MLC leaves created dose artifacts with regions of overdose in the CTV. As a result, the mean dose in spherical volumes centered in the middle of the CTV was on average 2.4 pp (5 mm radius sphere) and 1.3 pp (15 mm radius sphere) higher than planned (p = 0.002). CONCLUSIONS Intrafraction tumor motion can deteriorate the CTV dose of liver SBRT. The planned CTV dose coverage may be restored with KIM-guided MLC tracking. However, MLC tracking may have a tendency to create hotspots in the CTV.

中文翻译：

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千伏分次内监测指导的立体定向肝脏放射治疗的模拟多叶准直器跟踪：剂量学增益和目标过量趋势

目的 研究在肝脏立体定向放疗 (SBRT) 期间由千伏分次内监测 (KIM) 引导的多叶准直器 (MLC) 跟踪的潜在益处，并通过 MLC 跟踪了解靶标过量的趋势。方法 6 名植入了 2-3 个金标志物的肝脏 SBRT 患者使用每日锥形束 CT 设置，分三部分接受体积调制弧光疗法 (VMAT) 递送的 SBRT。CTV 到 PTV 的切缘在轴向平面上为 5 毫米，在头尾方向上为 10 毫米，该计划旨在提供 95% (CTV) 和 67% (PTV) 的最小目标剂量。通过对整个治疗过程中获得的 kV 透视图像进行治疗后分析估计的三维标记轨迹被假定为代表肿瘤运动。模拟了实时 KIM 引导的 MLC 跟踪。在实际非跟踪和模拟 MLC 跟踪治疗之间比较了 CTV D95（临床目标体积的 95% 的最小剂量）相对于计划的 D95 (ΔD95) 的减少。结果 MLC 追踪保持了所有 18 个部分的高 CTV 剂量覆盖率，ΔD95（平均值：0.2 个百分点 (pp)，范围：-1.7 至 1.9 pp）显着低于实际的非追踪治疗（平均值：6.3 pp 范围） : 0.6-16.0 pp) (p = 0.002)。MLC 跟踪垂直于 MLC 叶的大目标运动会在 CTV 中产生剂量伪影和过量区域。因此，以 CTV 中间为中心的球形体积中的平均剂量比计划 (p = 0.002) 平均高 2.4 pp（5 毫米半径球）和 1.3 pp（15 毫米半径球）。结论分次内肿瘤运动会降低肝脏SBRT的CTV剂量。可以通过 KIM 引导的 MLC 跟踪恢复计划的 CTV 剂量覆盖。但是，MLC 跟踪可能会在 CTV 中产生热点。