Das I J, Cheng E C, Freedman G, Fowble B
Department of Radiation Oncology, Fox Chase Cancer Center, Philadelphia, PA 19111, USA.
Int J Radiat Oncol Biol Phys. 1998 Aug 1;42(1):11-9. doi: 10.1016/s0360-3016(98)00200-4.
Radiation pneumonitis and cardiac effects are directly related to the irradiated lung and heart volumes in the treatment fields. The central lung distance (CLD) from a tangential breast radiograph is shown to be a significant indicator of ipsilateral irradiated lung volume. Retrospective analysis of the pattern of dose volume of lung and heart with actual volume data from a CT simulator in the treatment of breast cancer is presented with respect to CLD.
The heart and lung volumes in the tangential treatment fields were analyzed in 108 consecutive cases (52 left and 56 right breast) referred for CT simulation. All patients in this study were immobilized and placed on an inclined breast board in actual treatment setup. Both arms were stretched over head to avoid collision with the scanner aperture. Radiopaque marks were placed on the medial and lateral borders of the tangential fields. All patients were scanned in spiral mode with slice width and thickness of 3 mm each, respectively. The lung and heart structures as well as irradiated areas were delineated on each slice and respective volumes were accurately measured. The treatment beam parameters were recorded and the digitally reconstructed radiographs (DRRs) were generated for the measurement of the CLD and analysis.
Using CT data the mean volume and standard deviation of left and right lungs were 1307.7+/-297.7 cm3 and 1529.6+/-298.5 cm3, respectively. The magnitude of irradiated volume in left and right lung is nearly equal for the same CLD that produces different percent irradiated volumes (PIV). The left and right PIV lungs are 8.3+/-4.7% and 6.6+/-3.7%, respectively. The PIV data have shown to correlate with CLD with second- and third-degree polynomials; however, in this study a simple straight line regression is used to provide better confidence than the higher order polynomials. The regression lines for the left and right breasts are very different based on actual CT data. The slopes of regression lines for the left and right lung are 0.6%/mm and 0.5%/mm, respectively which is statistically different with thep value of 0.01. A maximum heart PIV of >3.0% is observed in 80% of the patients. The heart PIV is inversely correlated with gantry angle and weakly correlated with CLD.
The CT-simulator provides accurate volumetric information of the heart and lungs in the treatment fields. The lung PIV is directly correlated to the CLD (0.6%/mm and 0.5%/mm for the left and right lungs). Left and right lungs have different volumes and hence, different regression lines are recommended. An additional 12% lung volume could be irradiated in the supraclavicular field. Heart volume is not correlated with the CLD. The heart PIV is associated to the beam angle. Heart volume may not be accurately visualized in a tangential radiograph; however, this can be easily seen in a DRR with contour delineation and can be minimized with proper beam parameters iteratively with a virtual simulator. Lung and heart PIV along with dose volume histograms (DVH) are essential in reducing pulmonary and cardiac complications.
放射性肺炎和心脏效应与治疗野中照射的肺和心脏体积直接相关。来自乳腺切线位X线片的中心肺距离（CLD）被证明是同侧照射肺体积的一个重要指标。本文针对CLD，对乳腺癌治疗中利用CT模拟机的实际体积数据进行肺和心脏剂量体积模式的回顾性分析。
对108例连续接受CT模拟的病例（52例左侧乳腺和56例右侧乳腺）的切线治疗野中的心脏和肺体积进行分析。本研究中的所有患者在实际治疗设置中均被固定并置于倾斜的乳腺板上。双臂伸展过头以避免与扫描孔径碰撞。在切线野的内侧和外侧边界放置不透射线的标记。所有患者均以螺旋模式扫描，层厚和层间距均为3mm。在每层上勾勒出肺和心脏结构以及照射区域，并准确测量各自的体积。记录治疗束参数，并生成数字重建射线照片（DRR）用于CLD的测量和分析。
利用CT数据，左、右肺的平均体积和标准差分别为1307.7±297.7cm³和1529.6±298.5cm³。对于产生不同照射体积百分比（PIV）的相同CLD，左、右肺的照射体积大小几乎相等。左、右肺的PIV分别为8.3±4.7%和6.6±3.7%。PIV数据已显示与CLD呈二次和三次多项式相关；然而，在本研究中，使用简单的直线回归比高阶多项式能提供更好的可信度。基于实际CT数据，左、右乳腺的回归线差异很大。左、右肺回归线的斜率分别为0.6%/mm和0.5%/mm，这在统计学上有差异，p值为0.01。80%的患者观察到心脏最大PIV>3.0%。心脏PIV与机架角度呈负相关，与CLD呈弱相关。
CT模拟机能提供治疗野中心脏和肺的准确体积信息。肺PIV与CLD直接相关（左、右肺分别为0.6%/mm和0.5%/mm）。左、右肺体积不同，因此建议采用不同的回归线。锁骨上野可额外照射12%的肺体积。心脏体积与CLD无关。心脏PIV与射束角度有关。在乳腺切线位X线片中可能无法准确显示心脏体积；然而，在带有轮廓勾勒的DRR中很容易看到，并且可以通过虚拟模拟机迭代地使用适当的射束参数将其最小化。肺和心脏PIV以及剂量体积直方图（DVH）对于减少肺部和心脏并发症至关重要。
