Imaging the efficacy and side effects of CAR T-cell therapy in children and young adults.

CAR T-cell therapy is a transformative immunotherapy for pediatric patients with relapsed or refractory malignancies. Imaging plays a crucial role in evaluating treatment efficacy and detecting complications. This review provides time-specific guidance for radiologists on the imaging findings before and after CAR T-cell infusion and highlights how imaging supports clinical decision-making across the treatment course. Pre-treatment imaging at baseline focuses on ruling out active infection and quantifying residual tumor burden. In addition, quantitative imaging biomarkers can predict tumor response and toxicity risk. Between day 0–28 after CAR T-cell infusion, imaging is primarily performed to detect side effects, such as cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS). At day + 28, imaging provides early assessment of tumor response. Radiologists must recognize atypical immune-related response patterns at this time, including pseudoprogression and, less commonly, hyperprogression. Beyond day 28, imaging monitors for late side effects and infections, while also documenting ongoing tumor response or recurrence. Familiarity with these time-specific imaging patterns and pitfalls, coupled with knowledge of quantitative biomarkers, enables radiologists to differentiate toxicity from therapeutic effect, avoid misclassification of early immune-related changes, and optimize outcomes in pediatric CAR T-cell therapy.