Finazzi Tobias, van Sörnsen de Koste John R, Palacios Miguel A, Spoelstra Femke O B, Slotman Berend J, Haasbeek Cornelis J A, Senan Suresh
Department of Radiation Oncology, Amsterdam University Medical Centers, Location VUmc, de Boelelaan 1117, 1081 HV Amsterdam, The Netherlands.
Phys Imaging Radiat Oncol. 2020 May 20;14:17-23. doi: 10.1016/j.phro.2020.05.002. eCollection 2020 Apr.
Single-fraction stereotactic ablative radiotherapy (SABR) is an effective treatment for early-stage lung cancer, but concerns remain about the accurate delivery of SABR in a single session. We evaluated the delivery of single-fraction lung SABR using magnetic resonance (MR)-guidance.
An MR-simulation was performed in 17 patients, seven of whom were found to be unsuitable, largely due to unreliable tracking of small tumors. Ten patients underwent single-fraction SABR to 34 Gy on a 0.35 T MR-linac system, with online plan adaptation. Gated breath-hold SABR was delivered using a planning target volume (PTV) margin of 5 mm, and a 3 mm gating window. Continuous MR-tracking of the gross tumor volume (GTV) was performed in sagittal plane, with visual patient feedback provided using an in-room monitor. The real-time MR images were analyzed to determine precision and efficiency of gated delivery.
All but one patient completed treatment in a single session. The median total in-room procedure was 120 min, with a median SABR delivery session of 39 min. Review of 7.4 h of cine-MR imaging revealed a mean GTV coverage by the PTV during beam-on of 99.6%. Breath-hold patterns were variable, resulting in a mean duty cycle efficiency of 51%, but GTV coverage was not influenced due to real-time MR-guidance. On-table adaptation improved PTV coverage, but had limited impact on GTV doses.
Single-fraction gated SABR of lung tumors can be performed with high precision using MR-guidance. However, improvements are needed to ensure MR-tracking of small tumors, and to reduce treatment times.
单次大分割立体定向放射治疗（SABR）是早期肺癌的一种有效治疗方法，但对于单次治疗中SABR的精确实施仍存在担忧。我们评估了使用磁共振（MR）引导进行单次肺部SABR的实施情况。
对17例患者进行了MR模拟，其中7例被发现不适合，主要原因是小肿瘤的追踪不可靠。10例患者在0.35T MR直线加速器系统上接受了34Gy的单次SABR治疗，并进行了在线计划调整。使用5mm的计划靶区（PTV）边界和3mm的门控窗口进行门控屏气SABR治疗。在矢状面连续对大体肿瘤体积（GTV）进行MR追踪，并通过室内监视器向患者提供视觉反馈。分析实时MR图像以确定门控治疗的精度和效率。
除1例患者外，所有患者均在单次治疗中完成。室内总操作时间中位数为120分钟，SABR治疗单次时间中位数为39分钟。回顾7.4小时的电影MR成像显示，射束开启期间PTV对GTV的平均覆盖为99.6%。屏气模式各不相同，导致平均工作周期效率为51%，但由于实时MR引导，GTV覆盖不受影响。术中调整改善了PTV覆盖，但对GTV剂量影响有限。
使用MR引导可以高精度地进行肺部肿瘤的单次门控SABR治疗。然而，需要改进以确保对小肿瘤的MR追踪，并减少治疗时间。
