Berbeco Ross I, Hacker Fred, Zatwarnicki Chris, Park Sang-June, Ionascu Dan, O'Farrell Desmond, Mamon Harvey J
Department of Radiation Oncology, Brigham and Women's Hospital, Dana-Farber Cancer Institute and Harvard Medical School, Boston, Massachusetts 02115, USA.
Med Phys. 2008 Jul;35(7):3225-31. doi: 10.1118/1.2938514.
Stereotactic body radiation therapy is predicated on a high degree of targeting accuracy. However, inaccurate patient setup as well as intra-fractional motion can hinder the delivery of high doses preferentially to the target. To ensure that the coverage delivered to the patient is as planned, an image-guided verification system has been created to estimate the delivered dose retrospectively. This will not only aid the assessment of treatment techniques, but will also allow for more accurate dose response analysis. Patients with limited hepatic metastases from solid tumors were treated with SBRT. Implanted gold markers were used as target surrogates and a body frame and compression plate provided stereotactic localization and target immobilization, respectively. During treatment, an electronic portal imaging device (EPID), operating in cine mode, collected the exit dose. The sequences of images for each field were processed off-line using in-house software for registration and seed localization. The beam's-eye-view seed positions in the treatment images were compared to those in the DRR's to determine the target shifts in the imaging plane. These target shifts were then imported into the treatment planning software. Each original field was multiplied by the number of images taken during treatment. The calculated shift from each image was then applied to each of the new subfields. Summing all of these subfields together gives the dose distribution that was actually delivered to the patient. The dose-volume histograms for the planned and delivered distributions for four patients' complete treatments are shown. For two of the patients, underdosing due to a setup error or intra-fractional drift was not wholly resolved by subsequent fractions. For one of these patients two alternative corrective strategies have been applied, retrospectively, and the prescribed target coverage recovered for both. The delivered dose can be estimated using the information contained in cine EPID images acquired during irradiation. Calculating the dose actually delivered to the target will allow us to assess treatment procedures as well as more accurately report clinical results.
立体定向体部放射治疗基于高度的靶向准确性。然而，患者摆位不准确以及分次治疗期间的运动可能会妨碍优先向靶区输送高剂量。为确保输送给患者的剂量符合计划，已创建了一个图像引导验证系统，用于回顾性估计输送的剂量。这不仅有助于评估治疗技术，还将允许进行更准确的剂量反应分析。对患有实体瘤肝转移灶有限的患者进行了立体定向体部放射治疗。植入的金标记物用作靶区替代物，体架和压迫板分别提供立体定向定位和靶区固定。在治疗期间，以电影模式运行的电子门静脉成像设备（EPID）收集出射剂量。使用内部软件对每个射野的图像序列进行离线处理，以进行配准和种子定位。将治疗图像中的射野视角种子位置与数字重建放射影像（DRR）中的位置进行比较，以确定成像平面中的靶区移位。然后将这些靶区移位导入治疗计划软件。将每个原始射野乘以治疗期间拍摄的图像数量。然后将从每个图像计算出的移位应用于每个新的子射野。将所有这些子射野相加，得到实际输送给患者的剂量分布。展示了四名患者完整治疗的计划和实际输送剂量分布的剂量体积直方图。对于其中两名患者，由于摆位误差或分次治疗期间的漂移导致的剂量不足并未在后续分次中完全解决。对于其中一名患者，已回顾性应用了两种替代纠正策略，并且两者都恢复了规定的靶区覆盖。可以使用照射期间采集的电影EPID图像中包含的信息来估计输送的剂量。计算实际输送到靶区的剂量将使我们能够评估治疗程序，并更准确地报告临床结果。
