Kim Joshua, Glide-Hurst Carri, Doemer Anthony, Wen Ning, Movsas Benjamin, Chetty Indrin J
Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan.
Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan.
Int J Radiat Oncol Biol Phys. 2015 Jan 1;91(1):39-47. doi: 10.1016/j.ijrobp.2014.09.015. Epub 2014 Nov 7.
To describe and evaluate a method for generating synthetic computed tomography (synCT) images from magnetic resonance simulation (MR-SIM) data for accurate digitally reconstructed radiograph (DRR) generation and dose calculations in prostate cancer radiation therapy.
A retrospective evaluation was performed in 9 prostate cancer patients who had undergone MR-SIM in addition to CT simulation (CT-SIM). MR-SIM data were used to generate synCT images by using a novel, voxel-based weighted summation approach. A subset of patients was used for weight optimization, and the number of patients to use during optimization was determined. Hounsfield unit (HU) differences between CT-SIM and synCT images were analyzed via mean absolute error (MAE). Original, CT-based treatment plans were mapped onto synCTs. DRRs were generated, and agreement between CT and synCT-generated DRRs was evaluated via Dice similarity coefficient (DSC). Dose was recalculated, and dose-volume metrics and gamma analysis were used to evaluate resulting treatment plans.
Full field-of-view synCT MAE across all patients was 74.3 ± 10.9 HU with differences from CTs of 2.0 ± 8.1 HU and 11.9 ± 46.7 HU for soft tissue structures (prostate, bladder, and rectum) and femoral bones, respectively. Calculated DSCs for anterior-posterior and lateral DRRs were 0.90 ± 0.04 and 0.92 ± 0.05, respectively. Differences in D99%, mean dose, and maximum dose to the clinical target volume from CT-SIM dose calculations were 0.75% ± 0.35%, 0.63% ± 0.34%, and 0.54% ± 0.33%, respectively, for synCT-generated plans. Gamma analysis (2%/2 mm dose difference/distance to agreement) revealed pass rates of 99.9% ± 0.1% (range, 99.7%-100%).
Generated synCTs enabled accurate DRR generation and dose computation for prostate MR-only simulation. Dose recalculated on synCTs agreed well with original planning distributions. Further validation using a larger patient cohort is warranted.
描述并评估一种从磁共振模拟（MR - SIM）数据生成合成计算机断层扫描（synCT）图像的方法，以在前列腺癌放射治疗中准确生成数字重建射线照相（DRR）并进行剂量计算。
对9例除接受计算机断层扫描模拟（CT - SIM）外还接受了MR - SIM的前列腺癌患者进行回顾性评估。通过使用一种新颖的基于体素的加权求和方法，利用MR - SIM数据生成synCT图像。使用一部分患者进行权重优化，并确定优化过程中使用的患者数量。通过平均绝对误差（MAE）分析CT - SIM和synCT图像之间的亨氏单位（HU）差异。将基于CT的原始治疗计划映射到synCT上。生成DRR，并通过骰子相似系数（DSC）评估CT和synCT生成的DRR之间的一致性。重新计算剂量，并使用剂量体积指标和伽马分析来评估所得的治疗计划。
所有患者的全视野synCT MAE为74.3±10.9 HU，软组织结构（前列腺、膀胱和直肠）和股骨与CT的差异分别为2.0±8.1 HU和11.9±46.7 HU。前后位和侧位DRR的计算DSC分别为0.90±0.04和0.92±0.05。对于synCT生成的计划，临床靶体积的D99%、平均剂量和最大剂量与CT - SIM剂量计算的差异分别为0.7５%±0.35%、0.63%±0.34%和0.54%±0.33%。伽马分析（2%/2 mm剂量差异/一致性距离）显示通过率为99.9%±0.1%（范围为99.7% - 100%）。
生成的synCT能够为仅进行前列腺MR模拟时准确生成DRR和进行剂量计算。在synCT上重新计算的剂量与原始计划分布吻合良好。有必要使用更大的患者队列进行进一步验证。
