Medical Physics Department, Center of Oncology, Warsaw, Poland.
Strahlenther Onkol. 2010 Jun;186(6):327-33. doi: 10.1007/s00066-010-2086-5. Epub 2010 May 17.
To evaluate the performance of computed tomography (CT) systems of various designs as a source of electron density (rho(el)) data for treatment planning of radiation therapy.
Dependence of CT numbers on relative electron density of tissue-equivalent materials (HU-rho(el) relationship) was measured for several general-purpose CT systems (single-slice, multislice, wide-bore multislice), for radiotherapy simulators with a single-slice CT and kV CBCT (cone-beam CT) options, as well as for linear accelerators with kV and MV CBCT systems. Electron density phantoms of four sizes were used. Measurement data were compared with the standard HU-rhoel relationships predefined in two commercial treatment-planning systems (TPS).
The HU-rho(el) relationships obtained with all of the general-purpose CT scanners operating at voltages close to 120 kV were very similar to each other and close to those predefined in TPS. Some dependency of HU values on tube voltage was observed for bone- equivalent materials. For a given tube voltage, differences in results obtained for different phantoms were larger than those obtained for different CT scanners. For radiotherapy simulators and for kV CBCT systems, the information on rhoel was much less precise because of poor uniformity of images. For MV CBCT, the results were significantly different than for kV systems due to the differing energy spectrum of the beam.
The HU-rho(el) relationships predefined in TPS can be used for general-purpose CT systems operating at voltages close to 120 kV. For nontypical imaging systems (e.g., CBCT), the relationship can be significantly different and, therefore, it should always be measured and carefully analyzed before using CT data for treatment planning.
评估不同设计的计算机断层扫描（CT）系统作为放射治疗计划电子密度（ρ（el））数据来源的性能。
针对几种通用 CT 系统（单切片、多切片、大孔径多切片）、带单切片 CT 和千伏锥形束 CT（CBCT）选项的放射治疗模拟器以及带千伏和兆伏 CBCT 系统的直线加速器，测量了组织等效材料的 CT 数与相对电子密度的依赖性（HU-ρ（el）关系）。使用了四个尺寸的电子密度体模。将测量数据与两个商业治疗计划系统（TPS）中预定义的标准 HU-ρ（el）关系进行了比较。
所有接近 120kV 运行的通用 CT 扫描仪获得的 HU-ρ（el）关系彼此非常相似，且与 TPS 中预定义的关系非常接近。对于骨等效材料，观察到 HU 值与管电压之间存在一定的依赖性。对于给定的管电压，不同体模获得的结果差异大于不同 CT 扫描仪获得的结果差异。对于放射治疗模拟器和千伏 CBCT 系统，由于图像的均匀性较差，ρ（el）的信息精度要低得多。对于 MV CBCT，由于光束的能谱不同，结果与千伏系统有很大的差异。
TPS 中预定义的 HU-ρ（el）关系可用于接近 120kV 运行的通用 CT 系统。对于非典型成像系统（例如 CBCT），关系可能会有很大的不同，因此，在将 CT 数据用于治疗计划之前，应始终进行测量并仔细分析。
