Department of Radiation Oncology, Dana-Farber Cancer Institute, Brigham and Women's Hospital, and Harvard Medical School, Boston, Massachusetts, United States of America.
Department of Medical Physics, Faculty of Physics, Ludwig-Maximilians-Universität München, Garching, Germany.
Phys Med Biol. 2023 Aug 28;68(17). doi: 10.1088/1361-6560/ace876.
. Range uncertainty in proton therapy is an important factor limiting clinical effectiveness. Magnetic resonance imaging (MRI) can measure voxel-wise molecular composition and, when combined with kilovoltage CT (kVCT), accurately determine mean ionization potential (), electron density, and stopping power ratio (SPR). We aimed to develop a novel MR-based multimodal method to accurately determine SPR and molecular compositions. This method was evaluated in tissue-mimicking andporcine phantoms, and in a brain radiotherapy patient.. Four tissue-mimicking phantoms with known compositions, two porcine tissue phantoms, and a brain cancer patient were imaged with kVCT and MRI. Three imaging-based values were determined: SPR(CT-based Multimodal), SPR(MR-based Multimodal), and SPR(stoichiometric calibration). MRI was used to determine two tissue-specific quantities of the Bethe Bloch equation (, electron density) to compute SPRand SPR. Imaging-based SPRs were compared to measurements for phantoms in a proton beam using a multilayer ionization chamber (SPR).. Root mean square errors relative to SPRwere 0.0104(0.86%), 0.0046(0.45%), and 0.0142(1.31%) for SPR, SPR, and SPR, respectively. The largest errors were in bony phantoms, while soft tissue and porcine tissue phantoms had <1% errors across all SPR values. Relative to known physical molecular compositions, imaging-determined compositions differed by approximately ≤10%. In the brain case, the largest differences between SPRand SPRwere in bone and high lipids/fat tissue. The magnitudes and trends of these differences matched phantom results.. Our MR-based multimodal method determined molecular compositions and SPR in various tissue-mimicking phantoms with high accuracy, as confirmed with proton beam measurements. This method also revealed significant SPR differences compared to stoichiometric kVCT-only calculation in a clinical case, with the largest differences in bone. These findings support that including MRI in proton therapy treatment planning can improve the accuracy of calculated SPR values and reduce range uncertainties.
质子治疗中的射程不确定性是限制临床疗效的一个重要因素。磁共振成像（MRI）可以测量体素级别的分子组成，当与千伏 CT（kVCT）结合时，可以准确地确定平均电离能（）、电子密度和阻止本领比（SPR）。我们旨在开发一种新的基于 MRI 的多模态方法来准确确定 SPR 和分子组成。该方法在组织模拟体模和猪体模以及脑放射治疗患者中进行了评估。
使用 kVCT 和 MRI 对具有已知成分的四个组织模拟体模、两个猪组织体模和一个脑癌患者进行了成像。确定了三个基于成像的数值：SPR（基于多模态的 CT）、SPR（基于多模态的 MRI）和 SPR（化学计量校准）。MRI 用于确定 Bethe Bloch 方程的两个组织特异性量（和电子密度），以计算 SPR 和 SPR。
使用多层电离室（SPR）在质子束中对基于成像的 SPR 与体模的测量值进行了比较。
与 SPR 相比，SPR、SPR 和 SPR 的均方根误差分别为 0.0104（0.86%）、0.0046（0.45%）和 0.0142（1.31%）。最大误差出现在骨体模中，而软组织和猪体模在所有 SPR 值上的误差均<1%。与已知的物理分子组成相比，成像确定的组成差异约为≤10%。在脑病例中，SPR 和 SPR 之间的最大差异出现在骨和高脂质/脂肪组织中。这些差异的大小和趋势与体模结果相匹配。
我们的基于 MRI 的多模态方法在各种组织模拟体模中以高精度确定了分子组成和 SPR，这一点通过质子束测量得到了证实。该方法还在临床病例中显示出与化学计量 kVCT 仅计算相比，SPR 存在显著差异，最大差异出现在骨中。这些发现支持在质子治疗计划中包括 MRI 可以提高计算 SPR 值的准确性并降低射程不确定性。
