Radiation Medicine Program, Princess Margaret Hospital, University Health Network, Toronto, Ontario M5G 2M9, Canada.
Med Phys. 2010 Mar;37(3):1017-28. doi: 10.1118/1.3284368.
Late complications (cardiac toxicities, secondary lung, and breast cancer) remain a significant concern in the radiation treatment of Hodgkin's lymphoma (HL). To address this issue, predictive dose-risk models could potentially be used to estimate radiotherapy-related late toxicities. This study investigates the use of deformable image registration (DIR) and navigator channels (NCs) to reconstruct 3D lung models from 2D radiographic planning images, in order to retrospectively calculate the treatment dose exposure to HL patients treated with 2D planning, which are now experiencing late effects.
Three-dimensional planning CT images of 52 current HL patients were acquired. 12 image sets were used to construct a male and a female population lung model. 23 "Reference" images were used to generate lung deformation adaptation templates, constructed by deforming the population model into each patient-specific lung geometry using a biomechanical-based DIR algorithm, MORFEUS. 17 "Test" patients were used to test the accuracy of the reconstruction technique by adapting existing templates using 2D digitally reconstructed radiographs. The adaptation process included three steps. First, a Reference patient was matched to a Test patient by thorax measurements. Second, four NCs (small regions of interest) were placed on the lung boundary to calculate 1D differences in lung edges. Third, the Reference lung model was adapted to the Test patient's lung using the 1D edge differences. The Reference-adapted Test model was then compared to the 3D lung contours of the actual Test patient by computing their percentage volume overlap (POL) and Dice coefficient.
The average percentage overlapping volumes and Dice coefficient expressed as a percentage between the adapted and actual Test models were found to be 89.2 +/- 3.9% (Right lung = 88.8%; Left lung = 89.6%) and 89.3 +/- 2.7% (Right = 88.5%; Left = 90.2%), respectively. Paired T-tests demonstrated that the volumetric reconstruction method made a statistically significant improvement to the population lung model shape (p < 0.05). The error in the results were also comparable to the volume overlap difference observed between inhale and exhale lung volumes during free-breathing respiratory motion (POL: p = 0.43; Dice: p = 0.20), which implies that the accuracies of the reconstruction method are within breathing constraints and would not be the confining factor in estimating normal tissue dose exposure.
The result findings show that the DIR-NC technique can achieve a high degree of reconstruction accuracy, and could be useful in approximating 3D dosimetric representations of historical 2D treatment. In turn, this could provide a better understanding of the biophysical relationship between dose-volume exposure and late term radiotherapy effects.
霍奇金淋巴瘤（HL）放射治疗的迟发性并发症（心脏毒性、肺部和乳腺癌）仍然是一个重大问题。为了解决这个问题，预测剂量风险模型可以用于估计与放射治疗相关的迟发性毒性。本研究调查了使用变形图像配准（DIR）和导航通道（NC）从二维放射治疗计划图像重建 3D 肺模型，以便回顾性地计算接受二维计划治疗的 HL 患者的治疗剂量暴露情况，这些患者现在正在经历迟发性影响。
获取 52 例当前 HL 患者的三维计划 CT 图像。使用 12 组图像构建男性和女性人群肺模型。使用 23 个“参考”图像生成肺变形适应模板，通过使用基于生物力学的 DIR 算法 MORFEUS 将人群模型变形到每个患者特定的肺几何形状来构建。使用 2 个 D 重建射线照片测试 17 个“测试”患者，以测试重建技术的准确性。适应过程包括三个步骤。首先，通过胸廓测量将参考患者与测试患者匹配。其次，在肺边界上放置四个 NC（小感兴趣区）以计算肺边缘的 1D 差异。第三，使用 1D 边缘差异将参考肺模型适应到测试患者的肺。然后通过计算实际测试患者的 3D 肺轮廓与参考适应测试模型的百分比体积重叠（POL）和骰子系数来比较参考适应的测试模型。
发现适应和实际测试模型之间的平均重叠体积百分比和骰子系数分别为 89.2%±3.9%（右肺=88.8%；左肺=89.6%）和 89.3%±2.7%（右=88.5%；左=90.2%）。配对 T 检验表明，体积重建方法对人群肺模型形状有统计学意义的改善（p<0.05）。结果中的误差也与自由呼吸呼吸运动期间吸气和呼气肺体积之间观察到的体积重叠差异相当（POL：p=0.43；Dice：p=0.20），这意味着重建方法的精度在呼吸限制范围内，不会成为估计正常组织剂量暴露的限制因素。
结果表明，DIR-NC 技术可以达到很高的重建精度，可用于近似历史二维治疗的 3D 剂量表示。反过来，这可以更好地理解剂量-体积暴露与晚期放射治疗效果之间的生物物理关系。
