T1 mapping as a surrogate marker of chemotherapy response evaluation in patients with osteosarcoma.

Objectives: To characterize baseline T1 values of tumors, measure changes after the course of chemotherapy, and evaluate its potential as a marker of response assessment in patients with osteosarcoma.

Materials And Methods: A total of 35 patients (male:female = 27:8; age = 17.9 ± 6 years; metastatic:localized = 11:24) with biopsy-proven osteosarcoma were analyzed prospectively. All patients underwent magnetic resonance imaging before neoadjuvant chemotherapy (NACT) (baseline) and after NACT completion (follow-up), followed by surgery and histopathological evaluation. Histopathological necrosis served as the gold standard for assessing chemotherapy response (responder: ≥50% necrosis and non-responder: <50% necrosis). Three-dimensional spoiled gradient recalled echo images were acquired with varying flip angles (5, 10, 20, and 30) using a 1.5 Tesla scanner. T1 values were estimated in healthy muscle tissue and tumors at baseline and follow-up, and the relative percentage changes after NACT (ΔT1) were evaluated, and histogram analysis was performed to characterize the T1 value of the tumor and predict the NACT response using the Pearson correlation coefficient (r) and receiver operating characteristic curve analysis.

Results: At baseline, a significantly higher T1-mean (830.96 ± 193.88 msec versus 683.29 ± 210.00 msec; p = 0.003) and lower T1-skewness (0.86 ± 1.66 versus 1.60 ± 1.55; p = 0.02) were observed in osteosarcoma than healthy tissue. Responder:non-responder ratio was 13:22. At baseline, a significantly higher T1-mean (936.14 ± 193.17 msec versus 768.82 ± 169.25 msec; p = 0.018) and lower T1-skewness (-0.17 ± 0.85 versus 1.47 ± 1.73; p = 0.003) were observed among responders, than non-responders. After NACT, ΔT1 in tumor was significantly higher among responders than non-responders (-27.22 ± 12.17% versus -15.70 ± 18.99%; p = 0.034). ΔT1-mean and ΔT1-skewness after NACT were moderately correlated (r =  - 0.4, p = 0.030; r = 0.4, p = 0.011) with histopathological necrosis. For predicting NACT response, T1-mean and T1-skewness jointly produced an area under the curve (AUC) = 0.80 at baseline, and ΔT1-mean and ΔT1-skewness jointly produced AUC = 0.76 after NACT.

Conclusion: The mean and skewness of T1 values in osteosarcoma are potential non-invasive imaging markers for chemotherapy response assessment.