ABSTRACT The purpose of this study was to establish a high-performing radiomics strategy with machine learning from conventional and diffusion MRI to differentiate recurrent glioblastoma

(GBM) from radiation necrosis (RN) after concurrent chemoradiotherapy (CCRT) or radiotherapy. Eighty-six patients with GBM were enrolled in the training set after they underwent CCRT or

radiotherapy and presented with new or enlarging contrast enhancement within the radiation field on follow-up MRI. A diagnosis was established either pathologically or clinicoradiologically

(63 recurrent GBM and 23 RN). Another 41 patients (23 recurrent GBM and 18 RN) from a different institution were enrolled in the test set. Conventional MRI sequences (T2-weighted and

accuracy, sensitivity, specificity of 0.80, 78%, 66.7%, and 87%, respectively. In conclusion, the radiomics models models using other MRI sequences showed AUCs ranging from 0.65 to 0.66 in

the test set. The diffusion radiomics may be helpful in differentiating recurrent GBM from RN. . SIMILAR CONTENT BEING VIEWED BY OTHERS MACHINE LEARNING BASED DIFFERENTIATION OF GLIOBLASTOMA

FROM BRAIN METASTASIS USING MRI DERIVED RADIOMICS Article Open access 18 May 2021 PREDICTING HISTOLOGICAL GRADE IN PEDIATRIC GLIOMA USING MULTIPARAMETRIC RADIOMICS AND CONVENTIONAL MRI

FEATURES Article Open access 13 June 2024 MRI RADIOMICS BASED ON MACHINE LEARNING IN HIGH-GRADE GLIOMAS AS A PROMISING TOOL FOR PREDICTION OF CD44 EXPRESSION AND OVERALL SURVIVAL Article

Open access 03 March 2025 INTRODUCTION The current gold standard treatment for glioblastoma (GBM, World Health Organization [WHO] grade IV) is maximum safe tumor resection, followed by

concurrent chemoradiotherapy (CCRT) with temozolomide1,2. In cases of elderly patients with unmethylated 6-methylguanine-DNA methyltransferase (MGMT) promoter status or patients with

Karnofsky performance status (KPS) index lower than 70, radiotherapy (RT) alone is the standard treatment2,3. Radiation necrosis (RN) usually occurs within 3 years after radiation therapy

and is often indistinguishable from recurrent tumor because it manifests as an enhancing mass lesion with varying degrees of surrounding edema and progressive enhancement on serial magnetic

resonance imaging (MRI)4,5. Thus, distinguishing between recurrent GBM and RN has clinical importance in deciding the subsequent management; recurrence indicates treatment failure and

requires the use of additional anticancer therapies, whereas RN is treated conservatively. Multiple studies have made efforts to distinguish GBM recurrence from RN using various imaging

methods, including conventional imaging, diffusion-weighted imaging (DWI), diffusion tensor imaging, dynamic susceptibility contrast (DSC) imaging, MR spectroscopy, amide proton transfer

imaging, and positron emission tomography4,5,6,7,8,9,10,11,12,13. However, there is no gold standard imaging method for the differentiation between recurrence and RN, due to high degree of

overlapping findings. Currently, the definitive diagnosis is based on histopathology which is both invasive and difficult. In addition, the pathology results may be variable depending on the

surgical sampling sites due to the coexistence and admixture of recurrence and RN14. Radiomics involves the identification of ample quantitative features within images and the subsequent

data mining for information extraction and application15. Recent studies have shown promising results in predicting the molecular status, grade, and prognosis of gliomas16,17,18,19,20.

Because radiomics models use high-throughput features, there are prone to discover invisible information which are inaccessible with single-parameter analysis. The aim of this study was to

develop and validate a high-performing radiomic strategy using machine learning classifiers from conventional imaging and apparent diffusion coefficient (ADC) to differentiate recurrent GBM

from RN after concurrent CCRT or radiotherapy. RESULTS BASELINE CHARACTERISTICS OF THE PATIENTS The baseline demographic and clinical characteristics are summarized in Table 1. Of the 86

patients in the training set, 63 (73.3%) were classified as recurrent GBM and 23 (26.7%) as RN cases. The 41 patients in the test set consisted of 23 (56.1%) recurrent GBM and 18 (43.9%) RN

cases. There were no significant differences in age, sex, extent of resection, first line treatment (either CCRT or RT alone/RT plus temozolomide), total radiation dose, isocitrate

dehydrogenase 1 (IDH1) mutation status, and MGMT methylation status between patients with recurrent GBM and those with RN within both training and test sets. QUALITATIVE IMAGING ANALYSIS The

radiologists’ assessment of conventional imaging features showed no significant difference between recurrent GBM and RN in maximum lesion diameter, involvement of corpus callosum, and

“Swiss cheese” or “spreading wavefront” enhancement pattern in both the training set and test sets (all p-values > 0.05), respectively. BEST PERFORMING MACHINE LEARNING MODELS FROM

RADIOMICS FEATURES FOR DIFFERENTIATING RECURRENT GBM FROM RN IN THE TRAINING SET Using radiomic features, in each combination of the selected MRI sequence, the 3 feature selection, 3

classification methods, and 2 oversampling methods were trained. The performance of each combination of the models is shown in Fig. 1. In the training set, the area under the curve (AUCs) of

the models showing the best diagnostic performance ranged from 0.86 to 0.93 in each combination. AUCs with oversampling were higher than those without oversampling in all combinations. In

the ADC sequence, the combination of least absolute shrinkage and selection operator (LASSO) feature selection, and support vector machine (SVM) showed the best diagnostic performance in the

training set. The selected 18 features consisted of 3 first-order features, 10 s-order features, and 5 shape features (Detailed information at Supplementary Table 3). This model

demonstrated an area under the curve (AUC), accuracy, sensitivity, specificity of 0.90 (95% confidence interval [CI] 0.84–0.95), 80.5%, 78.3%, and 82.9%, respectively. In the T2WI (T2)

sequence, the combination of LASSO feature selection and SVM showed the best diagnostic performance in the training set with an AUC of 0.86 (95% CI 0.80–0.91). In the postcontrast T1WI (T1C)

sequence, the combination of mutual information (MI) feature selection and SVM showed the best diagnostic performance in the training set with an AUC of 0.91 (95% CI 0.86–0.95). In the

combined sequence (ADC + T2 + T1C), the combination of LASSO feature selection, and SVM showed the best diagnostic performance in the training set with an AUC of 0.93 (95% CI 0.89–0.97).

(Hyperparameters for each model are summarized at Supplementary Table 4). ROBUSTNESS OF RADIOMICS MODELS IN THE TEST SET In the independent test set, the model using ADC sequence with the

combination of LASSO feature selection and SVM showed the best diagnostic performance. This model demonstrated an AUC, accuracy, sensitivity, specificity of 0.80 (95% CI 0.65–0.95), 78%,

66.7%, and 87%, respectively. The radiomics models using other combination of MRI sequence showed poor performance (AUCs ranging from 0.65 to 0.66) in the test set, although it did not reach

significant difference from the ADC radiomics model (p-values of > 0.05). Table 2 summarizes the results of best performing models in training and test sets. DISCUSSION In this study, we

evaluated the ability of conventional and diffusion radiomics to differentiate recurrent GBM from RN. Several MR sequences and their combination were investigated and validated externally,

and among these models the diffusion radiomics model showed robustness with AUC of 0.80. RN has been reported to occur in approximately 9.8–44.4% of treated gliomas, which shows low

incidence than recurrent GBM6,9,21. In our study, the data imbalance was mitigated by using a systematic algorithm, which generates synthetic samples in the minority class22. The performance

was increased when synthetic minority over-sampling technique (SMOTE) was applied in our dataset (Fig. 1), showing its efficacy. Although recurrent GBM and RN have similar radiologic

appearances, they harbor distinct radiomic information that can be extracted and used to build a clinically relevant predictive model that discriminates recurrent GBM from RN. Our model may

aid in deciding the subsequent management of these patients. Although conventional findings such as “Swiss cheese” or “spreading wavefront” enhancement pattern have been reported to show

differences between recurrent high-grade glioma and RN in earlier studies5,6, these findings have subsequently been reported that they cannot be reliably used alone in differentiating

between the two conditions4,23. Moreover, these conventional imaging patterns are highly subjective. Various studies implementing advanced imaging parameters such as diffusion MRI, DSC MRI,

proton MR spectroscopy (MRS), amide proton transfer (APT) imaging, and positron emission tomography (PET) have shown promising results in differentiating recurrent GBM from

RN9,11,12,24,25,26. Although APT imaging has shown higher diagnostic performance than MRS27 or 11C-MET PET28 in differentiating recurrent GBM from RN, APT imaging is challenging due to long

scan times and limited coverage with high radiofrequency power. On the other hand, the accuracy of MRS and PET in differentiating recurrent GBM from RN has been questioned; a meta-analysis

has shown moderate sensitivity and specificity for MRS, 18F-FDG, and 11C-MET PET in distinguishing between recurrent GBM from RN29, whereas another study found no difference between

recurrence and necrosis groups using 18F-FDG and 11C-MET PET12. MRS and PET also have limited value in practical clinical settings due to their limited availability and low

cost-effectiveness. DSC MRI can readily distinguish between recurrent GBM and RN, as a biomarker of angiogenesis, with higher availability9,30. However, the relative cerebral blood volume

from DSC MRI can produce false positive or false negative results due to volume averaging, susceptibility artifacts, and overlapping portions in RN and recurrent GBM4,31. Also, the optimal

thresholds are different depending on the specific protocol9,32, and values derived from DSC imaging are relative values compared to absolute values from ADC maps. Moreover, the previous

studies using advanced imaging focused on single parameters such as mean values. In contrast to extraction of single parameters, radiomics extracts high-throughput quantitative features

within the regions of interest and has been reported to be a potentially useful approach for estimating the molecular status, grade, and prognosis of brain tumors16,17,19,20,33,34. Previous

studies have showed promising results in identifying recurrent brain tumor from RN using radiomics35,36,37. However, these studies were focused on recurrent brain metastases rather than

recurrent GBM, analyzing only conventional MRI sequences, and most datasets were small without external validation. Recent studies implemented radiomics model in differentiating recurrent

glioma from RN38,39; however the studies was either performed in a smaller dataset without external validation using only conventional MRI38, or performed radiomics analysis using 18F-FDG

and 11C-MET PET39, which are not routinely acquired imaging modalities. Our radiomics model implemented not only conventional MRI but also ADC map, which are recommended sequences in the

glioma protocol40,41, and showed that diffusion radiomics model could robustly differentiate recurrent GBM from RN better than any other radiomics model. However, models using conventional

MRI sequences (such as T2 or T1C) showed AUCs ranging from 0.650 to 0.662 in the test set. Moreover, multiparametric radiomics model did not show increased performance than the diffusion

radiomics model in the external validation. The signal intensities in conventional images may differ in different MRI protocol settings, leading to poor performance in an external validation

even after signal intensity normalization. On the other hand, ADC maps extract absolute values creating reliable feature extraction, which may be less affected by heterogeneous protocol

settings and consequently demonstrated high diagnostic performance in the external validation. In addition, our results may emphasize the importance of domain-specific knowledge in the

relatively small data settings of radiomics study42. Previous studies have shown that the ADC characteristics are more important than conventional characteristics in differentiating RN from

GBM4,7. The diffusion radiomics model is promising for reflecting the tumor microenvironment, since these values can contain biological information43,44. Although ADC value can be affected

by various factors, ADC in tumor is generally considered to be an index of tumor cellularity that reflects tumor burden45,46. On histopathological examination, recurrent GBM is characterized

by dense glioma cells, which limit water diffusion7. In contrast, RN is characterized by extensive fibrinoid necrosis, vascular dilatation, and gliosis47. The different histopathology and

spatial complexity may be reflected in diffusion radiomics, allowing the differentiation of the two entities31. In our study, the majority of significant radiomics features from the

diffusion radiomics model were various second-order features, suggesting that high‐throughput characteristics can provide more accurate assessment. The hypothesis for this observation is

that second-order features capture the spatial variation in signal intensity, which tend to extract information that may be incomprehensible and invisible to the naked eye. Recent studies

have demonstrated that second-order features also reflect the underlying histology48,49. However, a future study with histopathologic correlation is mandatory to prove our hypothesis of the

direct relationship between radiomic features in recurrent GBM and RN. Various features such as flatness, sphericity, mesh volume, and major axis length were included, suggesting that the

quantitative shape features may aid in differentiating in recurrent GBM from RN. Because there was no previous study that has quantified various shape features from the whole 3D lesion,

further studies are indicated to validate our results. Our study has several limitations. First, our study was retrospective with a small data size. Due to the relatively small size of the

test set, the 95% CIs of the AUCs in the test set tended to have a large range and some 95% CIs of the radiomics models cross 0.5. Future studies should be performed with a larger dataset.

Second, DSC imaging was not included due to lack of data in a portion of patients. Because DSC data is important in distinguishing recurrent GBM from RN50, further radiomics studies

implementing DSC data are warranted to evaluate the efficacy. Third, fluid-attenuation inversion recovery (FLAIR) sequence was not utilized in this study due to mixture of both precontrast

and postcontrast FLAIR sequences in the training set. Further studies are warranted to include the FLAIR sequence in radiomics analysis. Fourth, clinical factors were not integrated into the

radiomics model due to statistical insignificance in our dataset. However, as previous studies have stated the relationship between radiation doses or fractionation schemes with RN51,52,

future radiomics studies with larger datasets should perform multivariable analysis with clinically relevant features to differentiate recurrent GBM from RN. Fifth, cross-validation was

performed separately in the feature selection stage and the machine learning classification stage, which may have led to overfitted results. In conclusion, the diffusion radiomics model may

be helpful in differentiating recurrent GBM from RN. METHODS PATIENT POPULATION The Yonsei University Institutional Review Board waived the need for obtaining informed patient consent for

this retrospective study. All methods were carried out in accordance with relevant guidelines and regulation. For research limited to patients' medical records, access was cleared by

the Yonsei University Institutional Review Board and was supervised by a person (S-K.L.) who was fully aware of the confidentiality requirements. All of the study protocols were approved by

the Institutional Review Board (Severance Hospital, Yonsei University Health System Institutional Review Board, 2018-1472-002). Between February 2016 and February 2019, 90 patients with

pathologically diagnosed GBM (WHO grade IV) from our institution were reviewed in this study. The inclusion criteria were as follows: (1) GBM confirmed by histopathology; (2) postoperative

CCRT or RT, with a radiation dose ranging from 45 to 70 Gy; (3) subsequent development of a new or enlarging region of contrast enhancement within the radiation field 12 weeks after CCRT or

RT; and (4) surgical resection of the enhancing lesion or adequate clinicoradiological follow-up, which enabled us to diagnose recurrent GBM or RN. For clinicoradiological diagnosis, a final

diagnosis of recurrent GBM was made if the contrast-enhancing lesions gradually enlarged on more than two subsequent follow-up MRI studies performed at 2–3 month intervals (with a size

criterion of an increase of > 25% of the size of a measurable [> 1 cm] enhancing lesion according to the sum of the products of perpendicular dimensions) and the clinical symptoms of

patients showed gradual deterioration during follow-up28. Alternatively, a final diagnosis of RN was made if enhancing lesions gradually decreased on more than two subsequent follow-up MRI

studies performed at 2–3 month intervals and clinical symptoms improved during the follow-up period. Exclusion criteria were as follows: (1) processing error (n = 3), (2) absence of MRI

sequences (n = 1). Thus, a total of 86 patients were enrolled. Identical inclusion and exclusion criteria were applied and 41 patients from another institutional hospital (Asan Medical

Center, Seoul, Korea) were enrolled in the test set. The clinical characteristics of the patients included age, sex, KPS, IDH mutational status, MGMT promoter methylation status, and the

extent of resection of the tumor (gross total resection, subtotal resection, partial resection, or biopsy). PATHOLOGICAL DIAGNOSIS All patients underwent initial surgery, and histologic

confirmation was obtained according to the 2016 WHO classification46. Peptide nucleic acid-mediated clamping polymerase chain reaction and immunohistochemical analysis were performed to

detect the R132H mutation status in IDH153. MGMT promoter methylation status was diagnosed on the basis of methylation-specific polymerase chain reaction54. Twenty-two and 14 patients

underwent second-look operations in the training set and test set, respectively. In second-look operations, the pathological diagnoses included 17 recurrent GBM and 5 RN cases in the

training set, and 8 recurrent GBM and 6 RN cases in the test set, respectively. The diagnosis was made on the basis of histological findings in contrast-enhancing tissue obtained with

surgical tumor resection or image-guided. More than 5% viable tumor diagnosed during the histological examination by neuropathologists, were classified as a recurrent GBM9. MRI PROTOCOL In

the training set, all patients underwent MRI on a 3.0-T MRI scanner (Achieva or Ingenia, Philips Medical Systems) with an 8-channel head coil. The preoperative MRI sequences included T1WI,

T2, T1C, as well as ADC scans. After 5–6 min of administration of 0.1 mL/kg of gadolinium-based contrast material (Gadovist; Bayer), T1C were acquired. In the external validation set, MRI

exams were performed using a 3.0-T MRI scanner (Achieva, Philips Medical Systems) with an 8-channel head coil. Scaling and un-normalization of ADC pixel values generated at the scanner was

performed as previously described55. Constant level appearance (CLEAR) processing, a technique to achieve homogeneity correction by using coil sensitivity maps acquired in the reference

scan, was performed55. The acquisition protocols are described in further details in the Supplementary Table 1. QUALITATIVE IMAGE ANALYSIS Conventional images were analyzed by two

neuroradiologists (with 14 years and 7 years of experience) for maximum lesion diameter, involvement of corpus callosum, and “Swiss cheese” or “spreading wavefront” (ill-defined margins of

the enhancement) enhancement pattern, according to previous literature5,6. Discrepancies were settled by consensus. IMAGE PREPROCESSING AND RADIOMICS FEATURE EXTRACTION Preprocessing of T2,

T1C images, and ADC map was performed to standardize the data analysis among patients. Low-frequency intensity nonuniformity was corrected by applying the N4 bias correction algorithm as

implemented in the Advanced Normalization Tools (ANTs)56. Signal intensity normalization was used to reduce variance in the T2 and T1C images, by applying the WhiteStripe method from R

package57. T2, T1C, and ADC images were resampled to a uniform voxel size of 1 × 1 × 1 mm. T2 and ADC images were registered to the T1C image using affine transformation with normalized

mutual information as a cost function. Tumor segmentation was performed through a consensus discussion of two neuroradiologists (with 14 years and 7 years of experience), in order to select

the contrast-enhancing solid portion of the tumor on T1C images. Segmentation was performed semiautomatically with an interactive level-set region of interest, using edge-based and

threshold-based algorithms using 3D Slicer (version 4.11.0). There was no distortion in the ADC images that affected the segmented masks. Radiomic features were extracted from the segmented

mask, with a bin size of 32, with an open-source python-based module (PyRadiomics, version 2.0)58, which was adherent to the Image Biomarker Standardization Initiative (IBSI) guideline59. A

total of 93 radiomic features, including shape, first order features, and second-order features (Supplementary Table 2), were extracted from the mask. In addition, edge contrast calculation

was performed, that characterizes the tumor border, as previously described (Supplementary Information S1)60. The final set consisted of 263 radiomic features (14 shape features + 83

first-order and second-order 14 features × 3 sequences) for each patient. The data were processed using a multi-platform, open-source software package (3D slicer, version 4.6.2-1;

http://slicer.org). STATISTICAL ANALYSIS Baseline characteristics were compared between recurrent GBM and RN patients using chi-squared or Fisher’s exact test for categorical variables,

independent _t_-tests for normally distributed continuous variables, and Mann–Whitney _U_-tests for continuous variables without normal distribution. DeLong’s method was used to compare the

AUCs among the ADC radiomics model and other radiomics models in the training and test sets61. Statistical significance was set at P < 0.05. RADIOMIC FEATURE SELECTION AND MACHINE

LEARNING The schematic of the radiomics pipeline is shown in Fig. 2. All radiomic features were normalized using z-score normalization. For feature selection, the F-score, LASSO, or MI with

stratified ten-fold cross-validation were applied62. After feature selection, the machine learning classifiers were constructed separately using k-nearest neighbors (KNN), SVM, or AdaBoost,

with stratified ten-fold cross-validation. The optimal hyperparameters producing the highest AUC were selected by random search during cross-validation and subsequently used to get the final

model. In addition, to overcome data imbalance, each machine learning model was trained either without oversampling or with SMOTE (with a 1:1 ratio)22. Because we wanted to determine which

combination of MRI sequence shows the highest performance, the identical process was performed in each sequence (ADC, T2, T1C, and combined ADC, T2, and T1C model). Thus, various

combinations of classification models were trained to differentiate recurrent GBM from RN in the training set. AUC, accuracy, sensitivity, and specificity were obtained in the SMOTE

generated dataset in the training set, with a cutoff value according to Youden’s index. The different feature selection, classification methods, and oversampling were computed using

MatlabR2014b (Mathworks). Statistical significance was set at P < 0.05. DIAGNOSTIC PERFORMANCE IN THE TEST SET Based on the radiomics classification model in the training set, the best

combination of feature selection, classification methods, and oversampling in each sequence was used in the test set. The AUC, accuracy, sensitivity, and specificity were obtained with the

same cutoff from the training set. ABBREVIATIONS * ADC: Apparent diffusion coefficient * APT: Amide proton transfer * CI: Confidence interval * DWI: Diffusion-weighted imaging * DSC: Dynamic

susceptibility contrast * IDH1: Isocitrate dehydrogenase1 * KNN: K-nearest neighbors * KPS: Karnofsky performance status * LASSO: Least absolute shrinkage and selection operator * MGMT:

Oxygen 6-methylguanine-DNA methyltransferase * MI: Mutual information * MRI: Magnetic resonance imaging * MRS: Magnetic resonance spectroscopy * PET: Positron emission tomography * SMOTE:

Synthetic minority over-sampling technique * SVM: Support vector machine * T1C: Postcontrast T1WI * T2: T2WI * GBM: Glioblastoma * RN: Radiation necrosis * RT: Radiation therapy REFERENCES *

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ACKNOWLEDGEMENTS This research received funding from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, Information

and Communication Technologies & Future Planning (2017R1D1A1B03030440 and 2020R1A2C1003886). This research was also supported by Basic Science Research Program through the National

Research Foundation of Korea (NRF) funded by the Ministry of Education (2020R1I1A1A01071648). This research was also supported financially by the fund of Korean Society for Neuro Oncology.

AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Department of Radiology and Research Institute of Radiological Science and Center for Clinical Image Data Science, Yonsei University College of

Medicine, 50-1 Yonsei-ro, Seodaemun-gu, Seoul, 120-752, South Korea Yae Won Park, Sung Soo Ahn, Hwiyoung Kim & Seung-Koo Lee * Department of Computer Science, Yonsei University, Seoul,

South Korea Dongmin Choi * Department of Radiology and Research Institute of Radiology, University of Ulsan College of Medicine, Seoul, South Korea Ji Eun Park & Ho Sung Kim * Department

of Neurosurgery, Yonsei University College of Medicine, Seoul, South Korea Jong Hee Chang * Department of Pathology, Yonsei University College of Medicine, Seoul, South Korea Se Hoon Kim

Authors * Yae Won Park View author publications You can also search for this author inPubMed Google Scholar * Dongmin Choi View author publications You can also search for this author

inPubMed Google Scholar * Ji Eun Park View author publications You can also search for this author inPubMed Google Scholar * Sung Soo Ahn View author publications You can also search for

this author inPubMed Google Scholar * Hwiyoung Kim View author publications You can also search for this author inPubMed Google Scholar * Jong Hee Chang View author publications You can also

search for this author inPubMed Google Scholar * Se Hoon Kim View author publications You can also search for this author inPubMed Google Scholar * Ho Sung Kim View author publications You

can also search for this author inPubMed Google Scholar * Seung-Koo Lee View author publications You can also search for this author inPubMed Google Scholar CONTRIBUTIONS S.S.A. designed the

study. J.H.C. and S.H.K. compiled the institutional database. J.E.P. and H.S.K. provided external validation dataset. D.C, H.K., and S.-K.L designed the radiomics pipeline and D.C.

performed the radiomics analyses. Y.W.P. wrote the first draft of the manuscript, and S.S.A. provided the critical revision of the manuscript. S.-K.L. supervised the manuscript. All authors

contributed to and approved the final manuscript. CORRESPONDING AUTHOR Correspondence to Sung Soo Ahn. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing interests.

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ARTICLE CITE THIS ARTICLE Park, Y.W., Choi, D., Park, J.E. _et al._ Differentiation of recurrent glioblastoma from radiation necrosis using diffusion radiomics with machine learning model

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