Medical Physics Graduate Program, Department of Radiation Medicine, University of Kentucky, Lexington, KY, USA.
J Appl Clin Med Phys. 2021 Jun;22(6):162-171. doi: 10.1002/acm2.13268. Epub 2021 May 25.
PURPOSE/OBJECTIVES: This work seeks to evaluate the plan quality, treatment delivery efficiency, and accuracy of single-isocenter volumetric modulated arc therapy (VMAT) of abdominal/pelvic oligometastatic lymph nodes (LNs) stereotactic body radiation therapy (SBRT) on Halcyon Linac.
After completing the in-house multitarget end-to-end phantom testing and independent dose verification using MD Anderson's single-isocenter/multi-target (lung and spine target inserts) thorax phantom, eight patients with two to three abdominal/pelvic oligometastatic LNs underwent highly conformal single-isocenter VMAT-SBRT treatment using the Halcyon Linac 6MV flattening filter free (FFF) beam. Targets were identified using an Axumin PET/CT scan co-registered with planning CT images and a single-isocenter was placed between/among the targets. Doses between 25 and 36.25 Gy in 5 fractions were delivered. Patients were treated every other day. Plans were calculated in Eclipse with advanced AcurosXB algorithm for heterogeneity corrections. For comparison, Halcyon VMAT-SBRT plans were retrospectively generated for SBRT-dedicated TrueBeam with a 6MV-FFF beam using identical planning geometry and objectives. Target coverage, conformity index (CI), dose to 2 cm away from each target (D2cm) and dose to adjacent organs-at-risk (OAR) were evaluated. Additionally, various treatment delivery parameters including beam-on time were recorded.
Phantom measurements showed acceptable spatial accuracy of conebeam CT-guided Halcyon SBRT treatments including compliance with MD Anderson's single-isocenter/multi-targets phantom credentialing results. For patients, the mean isocenter to tumor center distance was 3.4 ± 1.2 cm (range, 1.5-4.8 cm). The mean combined PTV was 18.9 ± 10.9 cc (range, 5.6-39.5 cc). There was no clinically significant difference in dose to LNs, CI, D2cm and maximal doses to OAR between single-isocenter Halcyon and Truebeam VMAT-SBRT plans, although, Halcyon plans provided preferably lower maximal dose to adjacent OAR. Additionally, total monitor units, beam-on time and overall treatment time was lower with Halcyon plans. Halcyon's portal dosimetry demonstrated a high pass rate of 98.1 ± 1.6% for clinical gamma passing criteria of 2%/2 mm.
SBRT treatment of abdominal/pelvic oligometastatic LNs with single-isocenter VMAT on Halcyon was dosimetrically equivalent to TrueBeam. Faster treatment delivery to oligometastatic LNs via single-isocenter Halcyon VMAT can improve clinic workflow and patient compliance, potentially reducing intrafraction motion errors for well-suited patients. Clinical follow-up of these patients is ongoing.
本研究旨在评估在 Halcyon 医用直线加速器上采用单中心容积旋转调强放疗（VMAT）治疗腹部/盆腔寡转移淋巴结（LNs）立体定向体部放疗（SBRT）的计划质量、治疗效率和准确性。
在完成内部多靶端到端体模测试以及使用 MD 安德森的单中心/多靶（肺和脊柱靶插入物）胸部体模进行独立剂量验证后，对 8 例有 2-3 个腹部/盆腔寡转移 LN 的患者采用 Halcyon 医用直线加速器 6MV 无均整滤波器（FFF）射线进行高度适形的单中心 VMAT-SBRT 治疗。使用 Axumin PET/CT 扫描与计划 CT 图像配准来识别靶区，并在靶区之间/之间放置单中心。靶区接受 25-36.25Gy 共 5 次分割剂量照射。患者隔天治疗一次。在 Eclipse 中使用先进的 AcurosXB 算法进行不均匀性校正来计算计划。为了进行比较，回顾性地为具有 6MV-FFF 射线的 SBRT 专用 TrueBeam 生成了 Halcyon VMAT-SBRT 计划，采用相同的计划几何形状和目标。评估了靶区覆盖率、适形指数（CI）、靶区 2cm 处的剂量（D2cm）和相邻危及器官（OAR）的剂量。此外，还记录了各种治疗交付参数，包括射束开启时间。
体模测量显示，锥形束 CT 引导的 Halcyon SBRT 治疗具有可接受的空间精度，包括符合 MD 安德森的单中心/多靶体模认证结果。对于患者，平均等中心点到肿瘤中心的距离为 3.4±1.2cm（范围，1.5-4.8cm）。平均联合 PTV 为 18.9±10.9cc（范围，5.6-39.5cc）。单中心 Halcyon 和 Truebeam VMAT-SBRT 计划之间的淋巴结剂量、CI、D2cm 和最大 OAR 剂量没有临床意义上的差异，尽管 Halcyon 计划为相邻 OAR 提供了更好的低最大剂量。此外，Halcyon 计划的总监测单位、射束开启时间和总治疗时间较低。Halcyon 的门控剂量显示，临床伽马通过率为 98.1±1.6%，符合 2%/2mm 的通过率标准。
在 Halcyon 医用直线加速器上单中心 VMAT 治疗腹部/盆腔寡转移 LNs 在剂量学上与 TrueBeam 相当。通过单中心 Halcyon VMAT 更快地治疗寡转移 LNs 可以改善临床工作流程和患者依从性，有可能降低适合患者的分次内运动误差。这些患者的临床随访正在进行中。
