Van Dyk J
Int J Radiat Oncol Biol Phys. 1983 Jul;9(7):1035-41. doi: 10.1016/0360-3016(83)90394-2.
Radiotherapy of tumors within the thorax often requires radiation beams that traverse lung tissues. Not only do lungs consist of large volumes of low density tissues but, in addition, lung tissues are more radiosensitive than most other tissues. Computed tomography (CT) provides the detailed anatomic and geometric data ideally suited for accurate lung dose calculations. However, most radiotherapy centers do not have direct access to a CT scanner for planning purposes. In addition, it is argued by some that it is not necessary to use the CT pixel data directly for lung dose calculations but that it is sufficient to have the lung geometry outlined and to assume some average bulk density (not related to that specific patient) for the total lung volume. This study analyzes the potential errors in lung dose calculations when different lung density assumptions are made. The conclusions show that different levels of accuracy can be achieved with different levels of sophistication in lung density assumptions. However, the delivery of radiation absorbed dose to lung to an accuracy of 5% for all patients will require the detailed anatomical density data that are provided by CT.
胸部肿瘤的放射治疗通常需要穿过肺组织的辐射束。肺不仅由大量低密度组织组成，而且肺组织比大多数其他组织对辐射更敏感。计算机断层扫描（CT）提供了非常适合进行精确肺部剂量计算的详细解剖和几何数据。然而，大多数放疗中心在进行治疗计划时无法直接使用CT扫描仪。此外，一些人认为没有必要直接使用CT像素数据进行肺部剂量计算，只要勾勒出肺部几何形状并为整个肺体积假设一些平均体密度（与特定患者无关）就足够了。本研究分析了在做出不同肺部密度假设时肺部剂量计算中的潜在误差。结论表明，在肺部密度假设中采用不同程度的精细程度可以实现不同水平的准确性。然而，要为所有患者将肺部吸收剂量的输送精度控制在5%，将需要CT提供的详细解剖密度数据。
