Yu Victoria Y, Tran Angelia, Nguyen Dan, Cao Minsong, Ruan Dan, Low Daniel A, Sheng Ke
Department of Radiation Oncology, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California 90024.
Med Phys. 2015 Nov;42(11):6457-67. doi: 10.1118/1.4932631.
Significant dosimetric benefits had been previously demonstrated in highly noncoplanar treatment plans. In this study, the authors developed and verified an individualized collision model for the purpose of delivering highly noncoplanar radiotherapy and tested the feasibility of total delivery automation with Varian TrueBeam developer mode.
A hand-held 3D scanner was used to capture the surfaces of an anthropomorphic phantom and a human subject, which were positioned with a computer-aided design model of a TrueBeam machine to create a detailed virtual geometrical collision model. The collision model included gantry, collimator, and couch motion degrees of freedom. The accuracy of the 3D scanner was validated by scanning a rigid cubical phantom with known dimensions. The collision model was then validated by generating 300 linear accelerator orientations corresponding to 300 gantry-to-couch and gantry-to-phantom distances, and comparing the corresponding distance measurements to their corresponding models. The linear accelerator orientations reflected uniformly sampled noncoplanar beam angles to the head, lung, and prostate. The distance discrepancies between measurements on the physical and virtual systems were used to estimate treatment-site-specific safety buffer distances with 0.1%, 0.01%, and 0.001% probability of collision between the gantry and couch or phantom. Plans containing 20 noncoplanar beams to the brain, lung, and prostate optimized via an in-house noncoplanar radiotherapy platform were converted into XML script for automated delivery and the entire delivery was recorded and timed to demonstrate the feasibility of automated delivery.
The 3D scanner measured the dimension of the 14 cm cubic phantom within 0.5 mm. The maximal absolute discrepancy between machine and model measurements for gantry-to-couch and gantry-to-phantom was 0.95 and 2.97 cm, respectively. The reduced accuracy of gantry-to-phantom measurements was attributed to phantom setup errors due to the slightly deformable and flexible phantom extremities. The estimated site-specific safety buffer distance with 0.001% probability of collision for (gantry-to-couch, gantry-to-phantom) was (1.23 cm, 3.35 cm), (1.01 cm, 3.99 cm), and (2.19 cm, 5.73 cm) for treatment to the head, lung, and prostate, respectively. Automated delivery to all three treatment sites was completed in 15 min and collision free using a digital Linac.
An individualized collision prediction model for the purpose of noncoplanar beam delivery was developed and verified. With the model, the study has demonstrated the feasibility of predicting deliverable beams for an individual patient and then guiding fully automated noncoplanar treatment delivery. This work motivates development of clinical workflows and quality assurance procedures to allow more extensive use and automation of noncoplanar beam geometries.
先前已在高度非共面治疗计划中证明了显著的剂量学优势。在本研究中，作者开发并验证了一种个性化碰撞模型，用于实施高度非共面放射治疗，并测试了使用瓦里安TrueBeam开发者模式实现全流程自动化的可行性。
使用手持式3D扫描仪获取一个拟人化体模和一名人体受试者的表面，将其与TrueBeam机器的计算机辅助设计模型相结合，以创建一个详细的虚拟几何碰撞模型。该碰撞模型包括机架、准直器和治疗床的运动自由度。通过扫描具有已知尺寸的刚性立方体模来验证3D扫描仪的精度。然后通过生成300个对应于300个机架到治疗床和机架到体模距离的直线加速器方向，并将相应的距离测量值与其相应模型进行比较，来验证碰撞模型。直线加速器方向反映了对头、肺和前列腺均匀采样的非共面射束角度。物理系统和虚拟系统测量之间的距离差异用于估计治疗部位特定的安全缓冲距离，即机架与治疗床或体模之间碰撞概率为0.1%、0.01%和0.001%时的距离。通过内部非共面放射治疗平台优化的包含20条非共面射束的脑、肺和前列腺计划被转换为XML脚本以进行自动投送，并记录整个投送过程及时间，以证明自动投送的可行性。
3D扫描仪测量的14 cm立方体模的尺寸误差在0.5 mm以内。机架到治疗床和机架到体模的机器测量与模型测量之间的最大绝对差异分别为0.95 cm和2.97 cm。机架到体模测量精度降低归因于体模设置误差，这是由于体模末端略有变形和柔性。对于头、肺和前列腺治疗，碰撞概率为0.001%时估计的部位特定安全缓冲距离（机架到治疗床，机架到体模）分别为(1.23 cm, 3.35 cm)、(1.01 cm, 3.99 cm)和(2.19 cm, 5.73 cm)。使用数字直线加速器在15分钟内完成了对所有三个治疗部位的自动投送且无碰撞。
开发并验证了用于非共面射束投送的个性化碰撞预测模型。利用该模型，本研究证明了预测个体患者可投送射束并进而指导全自动化非共面治疗投送的可行性。这项工作推动了临床工作流程和质量保证程序的发展，以允许更广泛地使用非共面射束几何形状并实现自动化。
