Ahmad M, Nath R
Department of Therapeutic Radiology, Yale-New Haven Hospital and Yale University School of Medicine, Hew Haven, CT 06504, USA.
Int J Cancer. 2001 Feb 20;96(1):55-65. doi: 10.1002/1097-0215(20010220)96:1<55::aid-ijc6>3.0.co;2-#.
The specific aim of three-dimensional conformal radiotherapy is to deliver adequate therapeutic radiation dose to the target volume while concomitantly keeping the dose to surrounding and intervening normal tissues to a minimum. The objective of this study is to examine dose distributions produced by various radiotherapy techniques used in managing head and neck tumors when the upper part of the esophagus is also involved. Treatment planning was performed with a three-dimensional (3-D) treatment planning system. Computerized tomographic (CT) scans used by this system to generate isodose distributions and dose-volume histograms were obtained directly from the CT scanner, which is connected via ethernet cabling to the 3-D planning system. These are useful clinical tools for evaluating the dose distribution to the treatment volume, clinical target volume, gross tumor volume, and certain critical organs. Using 6 and 18 MV photon beams, different configurations of standard treatment techniques for head and neck and esophageal carcinoma were studied and the resulting dose distributions were analyzed. Film validation dosimetry in solid-water phantom was performed to assess the magnitude of dose inhomogeneity at the field junction. Real-time dose measurements on patients using diode dosimetry were made and compared with computed dose values. With regard to minimizing radiation dose to surrounding structures (i.e., lung, spinal cord, etc.), the monoisocentric technique gave the best isodose distributions in terms of dose uniformity. The mini-mantle anterior-posterior/posterior-anterior (AP/PA) technique produced grossly non-uniform dose distribution with excessive hot spots. The dose measured on the patient during the treatment agrees to within +/- 5 % with the computed dose. The protocols presented in this work for simulation, immobilization and treatment planning of patients with head and neck and esophageal tumors provide the optimum dose distributions in the target volume with reduced irradiation of surrounding non-target tissues, and can be routinely implemented in a radiation oncology department. The presence of a real-time dose-measuring system plays an important role in verifying the actual delivery of radiation dose.
三维适形放射治疗的具体目标是向靶区体积给予足够的治疗性辐射剂量，同时将对周围及中间正常组织的剂量保持在最低水平。本研究的目的是检查在治疗头颈部肿瘤且食管上部也受累时，各种放射治疗技术所产生的剂量分布情况。使用三维（3-D）治疗计划系统进行治疗计划。该系统用于生成等剂量分布和剂量体积直方图的计算机断层扫描（CT）图像直接从CT扫描仪获取，CT扫描仪通过以太网线缆连接到三维计划系统。这些是评估治疗体积、临床靶区体积、大体肿瘤体积以及某些关键器官剂量分布的有用临床工具。使用6兆伏和18兆伏光子束，研究了头颈部及食管癌标准治疗技术的不同配置，并分析了由此产生的剂量分布。在固体水模体中进行胶片验证剂量测定，以评估射野交界处剂量不均匀性的程度。使用二极管剂量测定法对患者进行实时剂量测量，并与计算剂量值进行比较。关于将对周围结构（即肺、脊髓等）的辐射剂量降至最低，单等中心技术在剂量均匀性方面给出了最佳的等剂量分布。小斗篷前后/后前（AP/PA）技术产生了严重不均匀的剂量分布，存在过多热点。治疗期间在患者身上测得的剂量与计算剂量的误差在±5%以内。本研究中提出的头颈部及食管肿瘤患者模拟、固定和治疗计划方案，在靶区体积中提供了最佳剂量分布，同时减少了对周围非靶组织的照射，并且可以在放射肿瘤学科室常规实施。实时剂量测量系统的存在在验证辐射剂量的实际输送方面起着重要作用。
