P11.07.a perfusion-mri based differentiation between early tumor progression and pseudoprogression in glioblastoma and its use in clinical practice

Abstract BACKGROUND Post-gadolinium MRI is considered the mainstay of radiological monitoring of treatment effects in patients with a glioblastoma. However, the radiotherapy(RT)-induced abnormality, pseudoprogression, is difficult to distinguish from real tumor growth. Perfusion MRI (pMRI), including Arterial Spin Labeling (ASL) and Dynamic Susceptibility Contrast (DSC), may help in this differentiation. Evaluation of RT effects is usually discussed during multidisciplinary team meetings (MDTM), after which a decision regarding (dis)continuation of anti-tumor treatment is made. It is currently unknown whether pMRI impacts such treatment decisions. This study evaluated how accurate pMRI and the MDTM are in distinguishing tumor progression from pseudoprogression in glioblastoma. MATERIAL AND METHODS Population and outcome: Glioblastoma patients who received postoperative RT were retrospectively included from 2015 to 2020. ASL, DSC, FLAIR and post-gadolinium 3D-T1 at 3 months post-RT were visually scored for probability of radiological tumor progression. These radiological scores, as well as the outcome of MDTM, were compared to the final outcome (i.e. tumor progression or pseudoprogression) set at 9 months after RT initiation. Statistical analysis: Diagnostic accuracy of pMRI, conventional MRI and MDTM was assessed by 2x2 tables, sensitivity and specificity (including AUC values). In case the MDTM was inconclusive, subsequent analysis was used to determine whether pMRI has additional value. A multivariable logistic regression model was constructed to assess which clinical parameters (age, surgery type, IDH mutation status, MGMT methylation status, KPS score, chemotherapy and pMRI evaluation) were associated with the outcome of the MDTM assessment. RESULTS Sixty-five patients with a glioblastoma met the inclusion criteria (40 male, mean age 60+/-13 years, median KPS of 90). For all METHODS , the sensitivity for detecting true disease progression was poor to moderate (32-62%). Although sensitivity was higher when adding pMRI to conventional imaging (56% versus 32%), specificity was lower (80% versus 93%). AUC values were comparable (range 0.63-0.74), but highest for MDTM evaluation (0.74). For the 26% of patients where MDTM was inconclusive, pMRI shows increased sensitivity compared to conventional MRI in detecting tumor progression (respectively 36% versus 0%). The multivariable regression analysis showed significant associations for KPS score (OR = 0.84 (95% CI: 0.77-0.91)) and radiological assessment based on pMRI with MDTM outcome (OR = 0.09 (95% CI: 0.02-0.52)). CONCLUSION This study shows that perfusion MRI has added value for detection of tumor progression within the MDTM assessment in clinical decision-making for glioblastomas, especially when the MDTM outcome is uncertain. For this decision, the role of perfusion MRI and the KPS score are most important.