We developed a method for automatic brain tumor segmentation using 3D U-Nets integration. We further analyzed relevant influencing factors and clinical significance of the brain glioma tumor core area and peritumor edema and reported that edema volume of glioma differ among GBM, astrocytoma and Oligodendroglioma (p < 0.05) These findings indicated that image features of edema play a role in glioma subtypes classification. Using the feature extraction parameters of the tumor and edema images obtained from this segmentation, we then developed a method to predict the molecular subtypes of adult-type diffuse gliomas based on the WHO 2021 classification. We constructed five classifiers that enabled the classification of glioma among extracted radiomics features and random forest showed the highest performance (AUC = 0.945 in the test set).
In the first phase of this study, we used BraTS21 public datasets, based on the nnUNet segmentation framework, and selected T1-CE and T2W-FLAIR sequences according to the actual imaging protocols of the clinical dataset for segmentation of the tumor core and whole tumor (tumor core and peri-tumor edema). Finally, utilizing pre-training of a public dataset and micro-tuning of a clinical dataset using only two imaging sequences, we achieved a performance close to those of two programs [15, 16] that performed well with BraTS21.The consensus recommendations for a standardized Brain Tumor Imaging Protocol [17, 18] suggest acquiring T1W, FLAIR, DWI, T2, and T1CE sequences. However, in clinical radiology practice, it is not always possible to acquire all imaging sequences of sufficiently complete and high quality for various reasons such as contrast intolerance and motion artifacts caused by unavoidable patient movement. Therefore, the method proposed in this study, which is based on fewer sequences while guaranteeing high accuracy in tumor segmentation, has a high value in clinical practice. Polina et al. [19] evaluated the contributions of individual sequences to multimodal tumor segmentation, and reported that just two imaging sequences, T1CE and T2W-FLAIR, achieved comparable performance as the four full imaging sequences under the same experimental conditions; however, their study used only conventional 3D U-net. Without adjusting the network structure and training parameters, the performance was not outstanding. Raphael et al. [20] investigated the optimal order of tumor imaging sequences incrementally, showing that the T2W-FLAIR sequence improved the segmentation of peritumoral edema. Based on the above studies, the results of the present study demonstrated that the segmentation model based on the nnUNet framework can be used for good segmentation performance of the tumor core and peritumor edema using a limited number of sequences (T1-CE + T2W-FLAIR).
WHO 2021 expands upon the trend that started in 2016, using key molecular biomarkers to define neoplastic entities and greatly reducing the dependency on morphological features for tumor classification [2]. Due to the close relationship between IDH mutations, 1p/19q co-deletion, and patient prognosis [21], previous studies have predicted IDH status and 1p/19q co-deletion using multimodal MRI radiomics features [22], residual convolutional neural networks [23, 24], and 3D-Dense-UNet [25]. Furthermore, a previous study showed that the molecular subtypes of diffuse gliomas can be predicted comprehensively using radiomics analysis [26]. If two separate methods are used, one predicting IDH status and one predicting 1p/19q co-deletion status, an IDH wild-type glioma can be predicted to have a 1p/19q co-deletion; however, as IDH wild-type and 1p/19q co-deletion are mutually exclusive [27], this is irrelevant to clinical reality.
In this study, we predicted the subtypes of adult-type diffuse gliomas using a trained model based on the latest classification of adult-type diffuse gliomas by the World Health Organization in 2021, using a well-trained segmentation network that extracts features from the tumor core and edema 3D VOI obtained by automated segmentation from T2W-FLAIR and T1CE sequences as inputs. The prediction performance achieved an AUC of 0.945. The prediction of each of the three subtypes was also highly accurate (GBM: 90.9%, A: 86.3%, and O: 92.4%; Table 1). The network identified “GBM” (100%) with higher sensitivity than “A” (57.1%) and “O” (33.3%). This result was not surprising because of the remarkable intra-tumor heterogeneity of IDH wild-type GBM with areas of necrosis, blood-brain barrier breakdown, and extensive perifocal edema [2], which likely aided the network in analyzing and identifying relevant MRI features to correctly identify IDH wild-type GBM with high sensitivity. Cluceru et al. [24] and Golestan Karami et al. [28] also performed a three-group classification analysis and observed higher sensitivity in the IDH-wildtype group compared with IDH-mutant astrocytoma and IDH-mutant 1p/19q-co-deleted oligodendroglioma.
Wang et al. [3] proposed a CNN-based comprehensive diagnostic model for the integrated classification of adult-type diffuse gliomas using deep learning from pathology images. However, pathology images can only be acquired after surgery or biopsy and cannot provide preoperative guidance, especially in cases that are difficult to diagnose preoperatively or when an operation is not performed. In contrast, our method provides a non-invasive alternative. Karami et al. [28] combined multi-shell diffusion with conventional MRI to apply deep learning for the molecular diagnosis of diffuse gliomas; however, their accuracy for the three molecular subtypes according to WHO 2021 was low (60 ± 5%). In addition, their study used an independent dataset from only one hospital. In contrast, our study utilized data from 424 cases in two datasets, the Zhongnan Hospital of Wuhan University and the UCSF-PDGM (TCIA) public database, to prevent an overestimation of the performance of our method. This also allowed our method to be robust to the heterogeneity naturally present in clinical imaging data, enabling its broad application in clinical practice. Tang et al. [29] used a multitask network to predict multiple tumor genotype-related features and overall survival in patients with glioblastoma. Because their method only works for patients with glioblastoma, the tumor grade must be known in advance, which complicates its use in preoperative situations when tumor grading is not yet known. Moreover, studies on the molecular subtypes of gliomas [5, 29, 30] generally require tumor segmentation as input, which is a time-consuming task. The automatic segmentation method for glioma tumors used in this study can be applied to prediction models.
Our tumor segmentation method has room for expansion. Tumor segmentation was used for tumor subtype prediction in this study. We did not study the effects of different sequences or different combinations of sequences on the segmentation tasks and results. Moreover, we applied the basic nnUNet framework and did not investigate the mechanism of attention, group normalization, or other potential methods for optimization. In addition, a larger number of samples and more clinical data can also enable further improvement in the performance and applicability of the methods developed in the present study.
Moreover, although our method showed good overall performance, the performance differed between tumor categories. The sensitivity for predicting oligodendrogliomas was low, which could be attributed to the lack of a central pathology review. This difference in the predictive performance between the subgroups can also be attributed to an imbalance in the data. Therefore, although our method may be relevant for certain subgroups, further improvement is necessary to ensure its relevance to the entire patient population.
In future studies, we aim to optimize our method by including perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) as these imaging modalities may contain additional information that can be linked to tumor genetic traits and aggressiveness [31].
In conclusion, we developed a prediction model for molecular glioma subtype in brain glioma using parameters obtained from the automated segmentation method we also developed in this study. We further identified influencing factors and confirmed the clinical significance of the tumor core area and peritumoral edema in brain gliomas. Additional studies are needed to further train and enhance our model and demonstrate its potential in the clinical setting.