Memorial Sloan Kettering Cancer Center, New York City, NY 10065, USA.
Memorial Sloan Kettering Cancer Center, New York City, NY 10065, USA.
Med Dosim. 2020;45(3):264-270. doi: 10.1016/j.meddos.2020.01.005. Epub 2020 Feb 20.
To evaluate proton dose calculation accuracy of optimized pencil beam scanning (PBS) plans on MR-derived synthetic-CTs for prostate patients.
Ten patient datasets with both a CT and an MRI were planned with opposed lateral proton beams optimized to single field uniform dose under an IRB-approved study. The proton plans were created on CT datasets generated by a commercial synthetic CT-based software called MRCAT (MR for Calculating ATtenuation) routinely used in our clinic for photon-based MR-only planning. A standard prescription of 79.2 Gy (RBE) and 68.4 Gy (RBE) was used for intact prostate and prostate bed cases, respectively. Proton plans were first generated and optimized using the MRCAT synthetic-CT (syn-CT), and then recalculated on the planning CT rigidly aligned with the syn-CT (aligned-CT) and a deformed planning CT (deformed-CT), which was deformed to match outer contour between syn-CT and aligned-CT. The same beam arrangement, total MUs, MUs/spot, spot positions were used to recalculate dose on deformed-CT and aligned-CT without renormalization. DVH analysis was performed on aligned-CT, deformed-CT, and syn-CT to compare D, V, V for PTV, PTVeval, and GTV as well as V, V for OARs.
The relative percentage dose difference between syn-CT and deformed-CT, were (0.17 ± 0.33 %) for PTVeval D and (0.07 ± 0.1 %) for CTV D. Rectum V, V and Bladder V were (2.76 ± 4.01 %), (11.6 ± 11.2 %), and (3.41 ± 2.86 %), respectively for the syn-CT, and (3.23 ± 3.63 %), (11.3 ± 8.18 %), and (3.29 ± 2.76 %), respectively for the deformed-CT, and (1.37 ± 1.84 %), (8.48 ± 6.67 %), and (4.91 ± 3.65 %), respectively for aligned-CT.
Dosimetric analysis shows that MR-only proton planning is feasible using syn-CT based on current clinical margins that account for a range uncertainty.
评估基于优化笔束扫描（PBS）计划的质子剂量计算在前列腺患者的 MR 衍生合成 CT 上的准确性。
在一项经机构审查委员会批准的研究中，对 10 名既有 CT 又有 MRI 的患者数据集进行了双侧质子束照射，质子束优化为单野均匀剂量。质子计划是在我们临床中常规用于光子单模 MR 计划的名为 MRCAT（MR 用于计算衰减）的商业合成 CT 软件生成的 CT 数据集上创建的。完整前列腺和前列腺床病例分别使用 79.2 Gy（RBE）和 68.4 Gy（RBE）的标准处方。首先在 MRCAT 合成 CT（syn-CT）上生成并优化质子计划，然后在与 syn-CT 刚性配准的计划 CT（aligned-CT）和变形计划 CT（deformed-CT）上重新计算，该变形 CT 用于匹配 syn-CT 和 aligned-CT 之间的外轮廓。不进行归一化，使用相同的射束排列、总 MU、MU/spot、spot 位置在变形 CT 和配准 CT 上重新计算剂量。在 aligned-CT、deformed-CT 和 syn-CT 上进行剂量体积直方图（DVH）分析，比较 PTVeval、PTV、CTV D、OARs 的 V、V 以及 PTV、GTV 的 V、V。
syn-CT 和 deformed-CT 之间的相对百分剂量差异为 PTVeval D 为（0.17 ± 0.33）%，CTV D 为（0.07 ± 0.1）%。直肠 V、V 和膀胱 V 分别为 syn-CT 的（2.76 ± 4.01）%、（11.6 ± 11.2）%和（3.41 ± 2.86）%，deformed-CT 的（3.23 ± 3.63）%、（11.3 ± 8.18）%和（3.29 ± 2.76）%，aligned-CT 的（1.37 ± 1.84）%、（8.48 ± 6.67）%和（4.91 ± 3.65）%。
剂量分析表明，使用基于当前临床边缘的基于 MR 的质子计划是可行的，这些边缘考虑了一定范围的不确定性。
