INTENSITY MODULATED RADIOTHERAPY--COMPUTATIONAL STUDIES

调强放射治疗(IMRT)技术旨在提供更高的肿瘤剂量照射，从而更好地控制肿瘤，同时减少对附近重要正常组织的剂量。这个项目的主要目标是使用计算机模拟来了解一系列建议的光子和质子调强放射治疗技术相对于传统技术的潜在好处。在第一阶段，将研究与调强放射治疗计划相关的技术问题，包括：全局优化与局部优化、肿瘤控制概率(TCP)模型假设的影响、治疗裕度和几何不确定性的影响、最佳照射所需的入射场数量和角度以及强度调制类型(全分辨率与节段性)。这些问题将使用一套来自患者CT数据集的二维(2D)测试问题进行详细研究，这些问题将涵盖广泛的潜在调强放射治疗计划问题。这一阶段的2D模拟结果将在更有限的三维(3D)模拟中进行测试。在第二阶段，将对几种已提出的调强放射治疗技术进行2D和3D模拟，包括：少场和多场强度调制共面光子传输、强度调制弧光治疗和一种新的强度调制质子束方法。每个计划都将通过不同的目标函数进行优化，最大Tcp和最大最小目标剂量，但限制在相同的正常组织剂量-体积限制。这些计划将与传统的光子技术计划进行比较。对于所有的调强放射治疗技术，至少将对四个不同的部位进行全3D研究：肺、前列腺、头颈部和腹部肿瘤。我们将调查可能表明一种调强放射治疗技术的剂量学优势的解剖学和几何学因素。建议的调强放射治疗技术将很难在临床试验中直接进行比较，除非规模有限。该项目的方法是使用相同的放射生物学和剂量学假设，对一系列建议的调强放射治疗技术进行计算比较，以帮助了解每种技术与传统治疗相比的相对潜在好处。我们假设调强放射治疗将需要3-5个以上的野，使用放射生物学的真实和全3D规划方法，以达到使用多野递送的可能的TCP水平。

Proposed intensity modulated radiation therapy (IMRT) techniques aim to provide higher tumor dose irradiation, and thereby better tumor control, while reducing dose to nearby important normal tissues. The main goal of this project is to use computer simulations to understand the potential benefits of a range of proposed photon and proton IMRT techniques relative to conventional techniques. In the first phase, technical issues relating to IMRT treatment planning will be investigated, including: global vs. local optimization, effects of tumor control probability (TCP) model assumptions, the effect of treatment margins and geometrical uncertainties, number and angles of incident fields needed for optimal irradiation, and type of intensity modulation (full resolution vs. segmental). These questions will be studied in detail using a suite of two- dimensional (2D) test problems, derived from patient CT data sets, which will cover a wide range of potential IMRT planning problems. Results from this phase of 2D simulations will be tested in more limited three-dimensional (3D) simulations. In the second phase, 2D and 3D simulations will be made comparing several proposed IMRT techniques, including: few- and many-field intensity modulated coplanar photon delivery, intensity-modulated arc therapy, and a novel intensity modulated proton beam method. Each plan will be optimized with alternative objective functions, maximum TCP and maximum minimum target dose, but constrained to the same normal tissue dose-volume limits. Those plans will be compared with conventional photon technique plans. At least four different sites will be studied in full 3D for all the IMRT techniques: lung, prostate, head and neck, and abdominal tumors. We will investigate the anatomical and geometrical factors which may indicate a dosimetric superiority of one IMRT technique over another. Proposed IMRT techniques will be difficult to compare directly in clinical trials except on a limited scale. The approach in this project is to conduct computational comparisons of a range of proposed IMRT techniques, using the same radiobiological and dosimetric assumptions, in order to help understand the relative potential benefits of each technique compared with conventional treatment. We hypothesize that IMRT will require more than 3-5 fields, using radiobiologically realistic and fully 3D planning methods, to reach the level of TCP possible using many-field delivery.