Department of Diagnostic Radiology and Clinical Oncology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong Special Administrative Region, China.
Oncology Centre, St. Teresa's Hospital, 327 Prince Edward Road, Hong Kong Special Administrative Region, China.
Radiat Oncol. 2020 Feb 18;15(1):42. doi: 10.1186/s13014-020-01488-5.
Although whole brain radiation therapy (WBRT) provides palliation and prophylaxis, reduces local recurrence probability and improves overall survival, it is evident that WBRT is associated with neurocognitive deficits due to radiation induced damage of the hippocampus. Therefore, minimizing hippocampal dose to the least possible level is of high clinical relevance. In dual-arc conventional volumetric modulated arc therapy (dac-VMAT), the large irradiation field for whole brain planned target volume (PTV) requires a wide jaw opening in which substantial low dose volume to the hippocampus may be produced due to suboptimal multi-leaf collimator (MLC) movements. The present study investigates the potential of a radiation therapy technique with split-arc and reduced field size, namely split-arc partial-field volumetric modulated arc therapy (sapf-VMAT) to spare the hippocampus during WBRT.
Computed tomography and magnetic resonance images of 20 patients with brain metastases were retrieved in this retrospective planning study. The hippocampus was manually delineated by single radiation oncologist strictly following the RTOG 0933 atlas definition. Plans delivering 30 Gy in 10 fractions were generated for each patient using dac-VMAT and sapf-VMAT. Dosimetric parameters from both techniques were compared by paired t-test.
The results demonstrated that radiation dose to the hippocampus was significantly reduced using sapf-VMAT relative to dac-VMAT plans. sapf-VMAT (7.86Gy, p = 0.001) had significantly lowered average D compared to dac-VMAT (9.23 Gy). Decrease in hippocampus D using sapf-VMAT (13.23 Gy, p = 0.001) was statistically significant when compared to dac-VMAT (16.33 Gy). The resulting mean dose to the hippocampus was 9.16 Gy for the for sapf-VMAT. Mean dose of sapf-VMAT was significantly lower than dac-VMAT (10.85 Gy, p < 0.05). In both eyes, sapf-VMAT demonstrated significantly lower D compared to dac-VMAT (p < 0.05). Whole brain PTV coverage was not compromised in both techniques.
sapf-VMAT has demonstrated significant dose reduction to the hippocampus and both eyes compared to dac-VMAT.
全脑放射治疗（WBRT）虽然能提供姑息治疗和预防作用，降低局部复发的概率，并提高总体生存率，但显然 WBRT 会引起因辐射导致的海马体损伤而出现神经认知缺陷。因此，将海马体的剂量降到最低水平具有重要的临床意义。在双弧常规容积调强弧形治疗（dac-VMAT）中，全脑计划靶区（PTV）的大照射野需要大的准直器开口，这会导致海马体的低剂量体积增大，这是由于多叶准直器（MLC）的运动不理想造成的。本研究旨在探讨一种具有分割弧和缩小照射野的放射治疗技术，即分割弧部分野容积调强弧形治疗（sapf-VMAT），在 WBRT 期间保护海马体的潜力。
在这项回顾性计划研究中，我们检索了 20 例脑转移患者的计算机断层扫描和磁共振图像。由一名放射肿瘤学家根据 RTOG 0933 图谱定义，对海马体进行手动勾画。为每位患者生成了 30Gy/10 次分割的 dac-VMAT 和 sapf-VMAT 计划。通过配对 t 检验比较两种技术的剂量学参数。
结果表明，与 dac-VMAT 计划相比，sapf-VMAT 可显著降低海马体的照射剂量。sapf-VMAT（7.86Gy，p=0.001）的平均 D 值明显低于 dac-VMAT（9.23Gy）。与 dac-VMAT（16.33Gy）相比，sapf-VMAT 降低了海马体 D 值（13.23Gy，p=0.001）。对于 sapf-VMAT，海马体的平均剂量为 9.16Gy。sapf-VMAT 的平均剂量明显低于 dac-VMAT（10.85Gy，p<0.05）。在两只眼睛中，sapf-VMAT 的 D 值明显低于 dac-VMAT（p<0.05）。两种技术的全脑 PTV 覆盖率均未受到影响。
与 dac-VMAT 相比，sapf-VMAT 显著降低了海马体和双眼的剂量。
