Westley Rosalyne L, Alexander Sophie E, Goodwin Edmund, Dunlop Alex, Nill Simeon, Oelfke Uwe, McNair Helen A, Tree Alison C
Department of Radiotherapy, The Royal Marsden NHS Foundation Trust, London, United Kingdom.
Division of Radiotherapy and Imaging, The Institute of Cancer Research, Sutton, United Kingdom.
Front Oncol. 2024 Jun 4;14:1379596. doi: 10.3389/fonc.2024.1379596. eCollection 2024.
We aimed to establish if stereotactic body radiotherapy to the prostate can be delivered safely using reduced clinical target volume (CTV) to planning target volume (PTV) margins on the 1.5T MR-Linac (MRL) (Elekta, Stockholm, Sweden), in the absence of gating.
Cine images taken in 3 orthogonal planes during the delivery of prostate SBRT with 36.25 Gray (Gy) in 5 fractions on the MRL were analysed. Using the data from 20 patients, the percentage of radiotherapy (RT) delivery time where the prostate position moved beyond 1, 2, 3, 4 and 5 mm in the left-right (LR), superior-inferior (SI), anterior-posterior (AP) and any direction was calculated.
The prostate moved less than 3 mm in any direction for 90% of the monitoring period in 95% of patients. On a per-fraction basis, 93% of fractions displayed motion in all directions within 3 mm for 90% of the fraction delivery time. Recurring motion patterns were observed showing that the prostate moved with shallow drift (most common), transient excursions and persistent excursions during treatment.
A 3 mm CTV-PTV margin is safe to use for the treatment of 5 fraction prostate SBRT on the MRL, without gating. In the context of gating this work suggests that treatment time will not be extensively lengthened when an appropriate gating window is applied.
我们旨在确定在不使用门控技术的情况下，在1.5T磁共振直线加速器（MRL，瑞典斯德哥尔摩的医科达公司）上，采用缩小的临床靶区体积（CTV）至计划靶区体积（PTV）边界，对前列腺进行立体定向体部放疗是否安全。
分析了在MRL上对前列腺进行立体定向体部放疗（SBRT）时，分5次给予36.25格雷（Gy）剂量过程中在3个正交平面采集的电影图像。利用20例患者的数据，计算了放疗（RT）过程中前列腺在左右（LR）、上下（SI）、前后（AP）及任意方向上移动超过1、2、3、4和5毫米的时间百分比。
在95%的患者中，90%的监测期内前列腺在任意方向上移动均小于3毫米。按分次计算，93%的分次在90%的分次照射时间内所有方向上的移动均在3毫米以内。观察到重复的运动模式，显示前列腺在治疗过程中出现浅漂移（最常见）、短暂偏移和持续偏移。
对于在MRL上进行的5分次前列腺SBRT治疗，不使用门控技术时，3毫米的CTV-PTV边界是安全的。在门控技术的背景下，这项工作表明，应用适当的门控窗口时，治疗时间不会大幅延长。
