Tseng Chia-Lin, Eppinga Wietse, Seravalli Enrica, Hackett Sara, Brand Eric, Ruschin Mark, Lee Young K, Atenafu Eshetu G, Sahgal Arjun
Department of Radiation Oncology, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, Canada.
Department of Radiotherapy, University Medical Center Utrecht, The Netherlands.
Radiother Oncol. 2017 Nov;125(2):273-279. doi: 10.1016/j.radonc.2017.09.036. Epub 2017 Oct 24.
We aimed to investigate the suitability of treating patients with single brain metastases using stereotactic radiosurgery (SRS) with the MRL and to characterize the dosimetric impact at tissue-air interfaces resulting primarily from the electron return effect (ERE).
24 patients treated for intact single brain metastases were analyzed. Three radiotherapy plans with the same prescribed dose were generated for each case: (1) noncoplanar volumetric modulated arc therapy (VMAT), (2) coplanar step-and-shoot intensity modulated radiotherapy (IMRT) on the MRL in the absence (MRLB=0), and (3) in the presence of the transverse magnetic field (MRLB=1.5). The plans were evaluated using cumulative dose-volume histograms and by calculation of Paddick conformity index (CI), V100%, V12Gy minus gross tumor volume (V12Gy - GTV), and V2Gy. At tissue-air boundaries, the dosimetric impact of the magnetic field was quantified using a 5 mm rim of tissue.
All plans met the target coverage and organs-at-risk planning objectives. Differences between all investigated dosimetric parameters significantly favored the VMAT plans as compared to the MRLB=0 and MRLB=1.5 plans, except for V2Gy. The mean V12Gy - GTV and V2Gy marginally favored the MRLB=0 plans compared to the MRLB=1.5 plans (mean difference: 0.45 cm, p = 0.0019 and 16.46 cm, p < 0.0001, respectively). The presence of the magnetic field resulted in a statistically significant but small increase in mean dose and D in the skin (0.08 Gy, p < 0.0001 and 0.6 Gy, p < 0.0001, respectively) and around air cavities (0.07 Gy, p = 0.0092 and 0.3 Gy, p = 0.0004, respectively).
It is feasible to generate stereotactic radiation plans that satisfy clinical requirements using the MRL in the setting of single brain metastases. The dosimetric impact of the magnetic field including the ERE at tissue-air boundaries is minor and does not negatively impact target conformity or dose gradient.
我们旨在研究使用磁共振直线加速器（MRL）的立体定向放射外科（SRS）治疗单发脑转移瘤患者的适用性，并描述主要由电子返回效应（ERE）导致的组织-空气界面处的剂量学影响。
分析了24例接受完整单发脑转移瘤治疗的患者。为每个病例生成了三个具有相同处方剂量的放射治疗计划：（1）非共面容积调强弧形放疗（VMAT），（2）在无横向磁场（MRLB = 0）情况下在MRL上进行的共面步进式调强放疗（IMRT），以及（3）在存在横向磁场（MRLB = 1.5）的情况下进行的共面步进式调强放疗。使用累积剂量-体积直方图并通过计算帕迪克适形指数（CI）、V100%、V12Gy减去大体肿瘤体积（V12Gy - GTV）和V2Gy来评估这些计划。在组织-空气边界处，使用5毫米宽的组织边缘对磁场的剂量学影响进行量化。
所有计划均达到了靶区覆盖和危及器官的计划目标。与MRLB = 0和MRLB = 1.5的计划相比，除V2Gy外，所有研究的剂量学参数之间的差异均显著有利于VMAT计划。与MRLB = 1.5的计划相比，平均V12Gy - GTV和V2Gy略微有利于MRLB = 0的计划（平均差异分别为：0.45厘米，p = 0.0019和16.46厘米，p < 0.0001）。磁场的存在导致皮肤中的平均剂量和D有统计学上显著但较小的增加（分别为0.08 Gy，p < 0.0001和0.6 Gy，p < 0.0001）以及气腔周围的平均剂量和D有统计学上显著但较小的增加（分别为0.07 Gy，p = 0.0092和0.3 Gy，p = 0.0004）。
在单发脑转移瘤的情况下，使用MRL生成满足临床要求的立体定向放射治疗计划是可行的。包括组织-空气边界处的ERE在内的磁场的剂量学影响较小，并且不会对靶区适形性或剂量梯度产生负面影响。
