Li Taoran, Shukla Gaurav, Peng Cheng, Lockamy Virginia, Liu Haisong, Shi Wenyin
Department of Radiation Oncology, Thomas Jefferson University, Philadelphia, PA, United States.
Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, United States.
Front Oncol. 2018 Mar 13;8:51. doi: 10.3389/fonc.2018.00051. eCollection 2018.
A recent randomized phase III clinical trial in patients with glioblastoma demonstrated the efficacy of tumor treating fields (TTFields), in which alternating electric fields are applied via transducer arrays to a patient's scalp. This treatment, when added to standard of care therapy, was shown to increase overall survival from 16 to 20.9 months. These results have generated significant interest in incorporating the use of TTFields during postoperative concurrent chemoradiation. However, the dosimetric impact of high-density electrodes on the scalp, within the radiation field, is unknown.
The dosimetric impact of TTFields electrodes in the radiation field was quantified in two ways: (1) dose calculated in a treatment planning system and (2) physical measurements of surface and deep doses. In the dose calculation comparison, a volumetric-modulated-arc-therapy (VMAT) radiation plan was developed on a CT scan without electrodes and then recalculated with electrodes. For physical measurements, the surface dose underneath TTFields electrodes were measured using a parallel plate ionization chamber and compared to measurements without electrodes for various incident beam angles and for 12 VMAT arc deliveries. Deep dose measurements were conducted for five VMAT plans using Scandidos Delta4 diode array: measured doses on two orthogonal diode arrays were compared.
In the treatment planning system, the presence of the TTFields device caused mean reduction of PTV dose of 0.5-1%, and a mean increase in scalp dose of 0.5-1 Gy. Physical measurement showed increases of surface dose directly underneath by 30-110% for open fields with varying beam angles and by 70-160% for VMAT deliveries. Deep dose measurement by diode array showed dose decrease of 1-2% in most areas shadowed by the electrodes (max decrease 2.54%).
The skin dose in patients being treating with cranial irradiation for glioblastoma may increase substantially (130-260%) with the addition of concurrent TTFields electrodes on the scalp. However, the impact of dose attenuation by the electrodes on deep dose during VMAT treatment is of much smaller, but measureable, magnitude (1-2%). Clinical trials exploring concurrent TTFields with cranial irradiation for glioblastoma may utilize scalp-sparing techniques to mitigate any potential increase in skin toxicity.
最近一项针对胶质母细胞瘤患者的随机III期临床试验证明了肿瘤治疗电场（TTFields）的疗效，即通过换能器阵列向患者头皮施加交变电场。该治疗方法与标准治疗方案联合使用时，可使总生存期从16个月延长至20.9个月。这些结果引发了人们对在术后同步放化疗期间使用TTFields的浓厚兴趣。然而，辐射野内高密度电极对头皮的剂量学影响尚不清楚。
通过两种方式对辐射野内TTFields电极的剂量学影响进行了量化：（1）在治疗计划系统中计算剂量；（2）对表面剂量和深部剂量进行物理测量。在剂量计算比较中，在没有电极的CT扫描上制定容积调强弧形放疗（VMAT）放射治疗计划，然后使用电极重新计算。对于物理测量，使用平行板电离室测量TTFields电极下方的表面剂量，并与不同入射束角度和12个VMAT弧形照射下无电极时的测量结果进行比较。使用Scandidos Delta4二极管阵列对五个VMAT计划进行深部剂量测量：比较两个正交二极管阵列上的测量剂量。
在治疗计划系统中，TTFields设备的存在导致计划靶体积（PTV）剂量平均降低0.5 - 1%，头皮剂量平均增加0.5 - 1 Gy。物理测量表明，对于不同束角的开放野，电极正下方的表面剂量增加30 - 110%，对于VMAT照射增加70 - 160%。二极管阵列进行的深部剂量测量显示，在电极遮挡的大多数区域剂量降低1 - 2%（最大降低2.54%）。
胶质母细胞瘤患者在进行颅脑放疗时，若头皮同时使用TTFields电极，皮肤剂量可能会大幅增加（130 - 260%）。然而，在VMAT治疗期间，电极对深部剂量的衰减影响较小，但可测量（1 - 2%）。探索胶质母细胞瘤颅脑放疗联合TTFields的临床试验可采用保留头皮的技术来减轻皮肤毒性的任何潜在增加。
