Laboratoire d'Evaluation de la Dose Interne (LEDI), Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Fontenay-Aux-Roses, France.
J Nucl Med. 2014 Mar;55(3):405-13. doi: 10.2967/jnumed.113.120444. Epub 2014 Feb 6.
In the last decades, selective internal radiation therapy (SIRT) has become a real alternative in the treatment of unresectable hepatic cancers. In practice, the activity prescription is limited by the irradiation of organs at risk (OAR), such as the lungs and nontumoral liver (NTL). Its clinical implementation is therefore highly dependent on dosimetry. In that context, a 3-dimensional personalized dosimetry technique--personalized Monte Carlo dosimetry (PMCD)-based on patient-specific data and Monte Carlo calculations was developed and evaluated retrospectively on clinical data.
The PMCD method was evaluated with data from technetium human albumin macroaggregates ((99m)Tc-MAA) evaluations of 10 patients treated for hepatic metastases. Region-of-interest outlines were drawn on CT images to create patient-specific voxel phantoms using the OEDIPE software. Normalized 3-dimensional matrices of cumulated activity were generated from (99m)Tc-SPECT data. Absorbed doses at the voxel scale were then obtained with the MCNPX Monte Carlo code. The maximum-injectable activity (MIA) for tolerance criteria based on either OAR mean absorbed doses (D(mean)) or OAR dose-volume histograms (DVHs) was determined using OEDIPE. Those MIAs were compared with the one recommended by the partition model (PM) with D(mean) tolerance criteria. Finally, OEDIPE was used to evaluate the absorbed doses delivered if those activities were injected to the patient and to generate the corresponding isodose curves and DVHs.
The MIA recommended using D(mean) tolerance criteria is, in average, 27% higher with the PMCD method than with the PM. If tolerance criteria based on DVHs are used along with the PMCD, an increase of at least 40% of the MIA is conceivable, compared with the PM. For MIAs calculated with the PMCD, D(mean) delivered to tumoral liver (TL) ranged from 19.5 to 118 Gy for D(mean) tolerance criteria whereas they ranged from 26.6 to 918 Gy with DVH tolerance criteria. Thus, using the PMCD method, which accounts for fixation heterogeneities, higher doses can be delivered to TL. Finally, absorbed doses to the lungs are not the limiting criterion for activity prescription. However, D(mean) to the lungs can reach 15.0 Gy.
Besides its feasibility and applicability in clinical routine, the interest for treatment optimization of a personalized Monte Carlo dosimetry in the context of SIRT was confirmed in this study.
在过去几十年中，选择性内部放射治疗（SIRT）已成为治疗不可切除肝癌的一种真正选择。实际上，活动处方受到危险器官（OAR）的辐射限制，例如肺和非肿瘤性肝（NTL）。因此，其临床实施高度依赖于剂量测定。在这种情况下，开发了一种基于患者特定数据和蒙特卡罗计算的三维个性化剂量测定技术-个性化蒙特卡罗剂量测定（PMCD），并对临床数据进行了回顾性评估。
使用 10 例接受肝转移治疗的患者的锝人白蛋白微球（（99m）Tc-MAA）评估数据评估了 PMCD 方法。在 CT 图像上绘制感兴趣区域轮廓，使用 OEDIPE 软件创建患者特定的体素体模。从（99m）Tc-SPECT 数据生成归一化的三维累积活性矩阵。然后，使用 MCNPX 蒙特卡罗代码获得体素尺度的吸收剂量。使用 OEDIPE 确定基于 OAR 平均吸收剂量（Dmean）或 OAR 剂量-体积直方图（DVH）的耐受标准的最大可注射量（MIA）。将这些 MIA 与基于 Dmean 耐受标准的分区模型（PM）推荐的 MIA 进行比较。最后，使用 OEDIPE 评估将这些活性物注入患者时所传递的吸收剂量，并生成相应的等剂量曲线和 DVH。
使用 Dmean 耐受标准推荐的 MIA 平均比 PMCD 方法高 27％。如果与 PMCD 一起使用基于 DVH 的耐受标准，则可以想象 MIA 至少增加 40％。对于使用 PMCD 计算的 MIA，肿瘤性肝（TL）的 Dmean 范围为 19.5 至 118 Gy，用于 Dmean 耐受标准，而对于 DVH 耐受标准，范围为 26.6 至 918 Gy。因此，使用 PMCD 方法，该方法考虑了固定异质性，可以向 TL 传递更高的剂量。最后，肺吸收剂量不是活动处方的限制标准。但是，Dmean 到肺可以达到 15.0 Gy。
除了在临床常规中具有可行性和适用性外，本研究还证实了 SIRT 背景下个性化蒙特卡罗剂量测定在治疗优化方面的重要性。
