Graham M V, Matthews J W, Harms W B, Emami B, Glazer H S, Purdy J A
Radiation Oncology Center, Washington University School of Medicine, St. Louis, MO 63110.
Int J Radiat Oncol Biol Phys. 1994 Jul 30;29(5):1105-17. doi: 10.1016/0360-3016(94)90407-3.
Several reports in the literature suggest that local-regional control and possibly survival could be improved for inoperable nonsmall cell lung cancer if the radiation dose to the target volume could be increased. Higher doses, however, bring with them the potential for increased side effects and complications of normal tissues. Three-dimensional treatment planning has shown significant potential for improving radiation treatment planning in several sites, both for tumor coverage and for sparing of normal tissue from high doses of radiation and, thus, has the potential of developing radiation therapy techniques that result in uncomplicated local-regional control of lung cancer. We have studied the feasibility of large-scale implementation of true three-dimensional technologies in the treatment of patients with cancers of the thorax.
CT scans were performed on 10 patients with inoperable nonsmall cell lung cancer to obtain full volumetric image data, and therapy was planned on our three-dimensional radiotherapy treatment planning system. Target volumes were determined using the new ICRU nomenclature--Gross Tumor Volume, Clinical Target Volume, and Planning Target Volume. Plans were performed according to our standard treatment policies based on traditional two-dimensional radiotherapy treatment planning methodologies and replanned using noncoplanar three-dimensional beam techniques. The results were quantitatively compared using dose-volume histograms, dose-surface displays, and dose statistics.
Target volume delineation remains a difficult problem for lung cancer. Defining Gross Tumor Volume and Clinical Target Volume may depend on window and level settings of the three-dimensional radiotherapy treatment planning system, suggesting that target volume delineation on hard copy film is inadequate. Our study shows that better tumor coverage is possible with three-dimensional plans. Dose to critical structures (e.g., the heart) could often be reduced (or at least remain acceptable) using noncoplanar beams even with dose escalation to 75 to 80 Gy for the planning volume surrounding the Gross Target Volume.
Commonly used beam arrangements for treatment of lung cancer appear to be inadequate to safely deliver tumor doses of higher than 70 Gy. Although conventional treatment techniques may be adequate for tumor coverage, they are inadequate for sparing of normal tissues when the prescription dose is escalated. The ability to use noncoplanar fields for such patients is a major advantage of three-dimensional planning. This capability led to better tumor coverage and reduced dose to critical normal tissues. However, this advantage was achieved at the expense of a greater time commitment by the treatment planning staff (particularly the radiation oncologist) and a greater complexity of treatment delivery. In summary, three-dimensional radiotherapy treatment planning appears to provide the radiation oncologist with the necessary tools to increase tumor dose, which may lead to increased local-regional control in patients with lung cancer while maintaining normal tissue doses at acceptable tolerance levels.
文献中的多篇报道表明，如果能够提高对靶区的放射剂量，不可切除的非小细胞肺癌的局部区域控制以及可能的生存率或许可以得到改善。然而，更高的剂量会带来正常组织副作用和并发症增加的可能性。三维治疗计划在多个部位已显示出显著潜力，既能改善肿瘤覆盖情况，又能使正常组织免受高剂量辐射，因此有潜力开发出能实现肺癌局部区域控制且无并发症的放射治疗技术。我们研究了在胸部肿瘤患者治疗中大规模应用真正三维技术的可行性。
对10例不可切除的非小细胞肺癌患者进行CT扫描，以获取完整的容积图像数据，并在我们的三维放射治疗计划系统上制定治疗计划。使用新的ICRU命名法确定靶区——大体肿瘤体积、临床靶体积和计划靶体积。计划按照基于传统二维放射治疗计划方法的标准治疗策略进行，并使用非共面三维射束技术重新计划。结果通过剂量体积直方图、剂量表面显示和剂量统计进行定量比较。
靶区勾画对于肺癌来说仍然是个难题。定义大体肿瘤体积和临床靶体积可能取决于三维放射治疗计划系统的窗宽和窗位设置，这表明在硬拷贝胶片上进行靶区勾画并不充分。我们的研究表明，三维计划能够实现更好的肿瘤覆盖。即使将大体靶体积周围的计划体积剂量提高到75至80 Gy，使用非共面射束通常也能降低（或至少保持可接受水平）关键结构（如心脏）的剂量。
用于肺癌治疗的常用射束排列似乎不足以安全地给予高于70 Gy的肿瘤剂量。虽然传统治疗技术可能足以覆盖肿瘤，但当处方剂量增加时，它们在保护正常组织方面并不充分。对这类患者使用非共面射野的能力是三维计划的一个主要优势。这种能力实现了更好的肿瘤覆盖，并降低了关键正常组织的剂量。然而，这一优势是以治疗计划人员（尤其是放射肿瘤学家）投入更多时间以及治疗实施的复杂性增加为代价的。总之，三维放射治疗计划似乎为放射肿瘤学家提供了增加肿瘤剂量所需的工具，这可能会提高肺癌患者的局部区域控制率，同时将正常组织剂量维持在可接受的耐受水平。
