“虚拟患者”为放射治疗模拟实时器官运动

美国国立卫生研究院（NIH）批准资助伦斯勒理工学院的研究员2百万美元，用于研发一种应用物理原理实时虚拟患者呼吸的模型,即3D模型联合时间变量所得到的4D模型，它的应用能够明显改善肺癌和肝癌放疗的精确度和效果。

在德克萨斯州圣安东尼市的癌症治疗和研究中心，George Xu(生物医学工程和核医学教授)和Suvranu De(机械工程学副教授)与临床专业的同事进行多学科合作，研发4D可视图象人（4-D VIP－Man）。这种虚拟模型是Xu教授正在进行的3-D VIP-Man计划的延伸项目。此项目是一种先进的电脑模型，能用3-D技术模拟射线如何影响人体的器官和组织。

Xu教授认为，活人不同于静止的生物，而在肿瘤的放疗和成像中，像肺脏或者心脏这样能够运动的器官是主要的干扰因素。为了判断有效放射计量及其精确数值，医生必须考虑如呼吸运动和空气容积变化这些问题，它们在放疗过程中会受生理因素影响。实时模拟能够使得医生在短时间片段内能观测到肺、肝、肾和心相对与外射线是静止的。在临床治疗中，做到这点即意味着，医生在为运动的肿瘤作放疗时能更有把握。4-D VIP－Man可以让医生和医学物理学家精确地预测和监测这些解剖改变，从而在任何时候都能提供最有效的治疗。但4-D VIP－Man很难研制。

现在，Xu教授和De副教授正集中精力研究呼吸功能。应用先进的计算机技术，模拟肺的运动是可行的；但是，不能做到实时模拟。对于精确放疗来说，应用物理技术实时虚拟人体功能能最终解决这个问题。这项计划的主要难度在于如何研发相应的运算法则，从而依照组织真实的生物力学性质实时模拟肺及临近组织的运动。Xu教授预测，基于物理学的4-D VIP-Man将最终在生物医学领域更广泛地用作解剖模型，帮助治疗有呼吸道疾病和心脏病的患者。同时，他将通过计算机学人体影像协会（http://www.virtualphantoms.org）与全世界的研究者合作，继续研究3-D VIP-Man，创造虚拟患者的“家族谱” 。

Xu教授以前的学生Chengyu Shi（临床医学物理学家）和Martin Fuss（放射肿瘤学家）认为，在解决肺的运动问题后，放疗效果会更好。在得知他们的兴趣后，Xu和田纳西州的研究组开始合作。在与De副教授（他曾用3-D VIP-Man技术模拟外科手术中组织的变形）联系后，将3-D VIP-Man改进为4-D VIP-Man的想法就产生了。

从1997年以来，Xu一直致力于应用先前的可视人体工程计划（Visible Human Project ）来研究3-D VIP-Man，其数据集来源于美国国家医学图书馆，经费来源于NIH和国家科学基金会CAREER奖金。新的4年科研基金由美国国家医学图书馆（NIH的一部分）资助。

“Virtual Patient” To Simulate Real-time Organ Motions For Radiation Therapy

With a $2 million grant from the National Institutes of Health (NIH), researchers from Rensselaer Polytechnic Institute are developing a physics-based virtual model that can simulate a patient's breathing in real time。When used in conjunction with existing 3-D models, adding the fourth dimension of time could significantly improve the accuracy and effectiveness of radiation treatment for lung and liver cancers.

。George Xu, professor of nuclear and biomedical engineering, and Suvranu De, associate professor of mechanical engineering, have formed a multidisciplinary collaboration with clinical colleagues at the Cancer Therapy & Research Center in San Antonio, Texas, to develop the 4-D Visible Photographic Man (VIP-Man)。This virtual model is an extension of Xu's ongoing project involving the 3-D VIP-Man, which is an advanced computer model that simulates in 3-D how radiation affects the organs and tissues in the human body.

"Live patients are not static beings, and a moving organ such as the lung or heart is a main concern in radiation treatment or imaging of tumors that are affected by such organ movement," Xu said。"In order to determine accurate and effective radiation dosages, doctors must consider such issues as the breathing function and air volume change that are affected by several physiological factors over the course of the radiation treatment."

Real-time simulations could allow doctors to spot the small fractions of time when the lungs, liver, kidneys, and eventually the heart, are stationary relative to the external radiation beams。These opportune moments during the actual therapy mean that doctors will have more confidence delivering the radiation to a moving tumor.

"The 4-D VIP-Man will allow doctors and medical physicists to accurately predict and monitor these anatomical changes to provide the most effective treatment possible at any given time," Xu said.

The fourth dimension of the VIP-Man is not easily achieved, according to Xu。Currently Xu and De are focusing their energy on respiratory function。"Using advanced computational tools, it is possible to simulate lung movement; however, not in real time," De said。"For effective radiation therapy, physics-based real-time performance offers the ultimate solution."

The key challenge in this project is to develop the algorithms that will make the virtual lungs and adjacent tissues move in real time according to realistic tissue biomechanical properties, De said.

Xu expects that the physics-based 4-D VIP-Man will eventually be used as an even more general anatomical modeling tool for the biomedical community to help patients with respiratory and cardiac diseases。At the same time, Xu will continue to work on the 3-D VIP-Man to create a "family" of virtual patients, ranging in ages and sizes, in collaboration with researchers worldwide through the Consortium of Computational Human Phantoms (http://www.virtualphantoms.org), co-founded by Xu.

The collaboration with the group in Texas came about when Xu's former student, Chengyu Shi, a clinical medical physicist, and Martin Fuss, a radiation oncologist, expressed their interests to develop better radiation treatment by accounting for lung movement。Xu contacted De, who had been using the 3-D VIP-Man to simulate tissue deformation for surgical procedures, and the idea to take 3-D VIP-Man into the fourth dimension was born.

Xu has been working on the 3-D VIP-Man since 1997 using the original Visible Human Project dataset provided by the National Library of Medicine, also funded by several grants from NIH as well as a National Science Foundation CAREER grant。The new four-year, $2 million grant is funded by the National Library of Medicine, which is part of NIH.