Prognostic Significance of Positron Emission Tomography Delta Radiomics Following Bridging Therapy in Patients with Large B-Cell Lymphoma Undergoing CAR T-Cell Therapy

PURPOSE/OBJECTIVE(S)

CAR T-cell therapy is routinely used as a treatment option for relapsed/refractory large B-cell lymphoma (LBCL). Bridging therapy radiation therapy (bRT) is increasingly being utilized prior to chimeric antigen receptor (CAR) T-cell therapy for large B-cell lymphoma (LBCL). It is unknown how the extent of debulking as a result of bRT impacts outcomes following CAR T-cell infusion. We hypothesized that the extent of debulking is prognostic of overall response to therapy.

MATERIALS/METHODS

We reviewed patients with LBCL treated with bRT followed by commercially available CAR T-cell therapy between 2017 and 2022. Patients required a F-fluorodeoxyglucose (FDG) positron emission tomography (PET) scan prior to bRT and between completion of bRT and CAR T-cell infusion. On each scan, metabolic tumor volume (MTV), maximum standardized uptake value (SUVmax), SUVmean, and total lesion glycolysis (TLG) were determined. Delta-radiomics based on changes of these values between scans in patients overall and irradiated sites were then calculated. Optimal cut points were determined using maximally selected log-rank. The primary endpoints were progression-free survival (PFS) and local control (LC), measured from CAR T-cell infusion by Kaplan-Meier and Fine-Gray competing risk survival analyses, respectively.

RESULTS

Twenty-three patients with LBCL with 33 irradiated sites were reviewed. All metabolically active disease was treated in 10 patients. Median equivalent dose in 2 Gy fractions (EQD2) was 26 Gy (14-44). Median interval from bRT to PET was 9 days (2-30). Following bRT, 2 patients achieved complete responses, 16 had partial responses, and 5 had progressive disease. Five irradiated sites progressed through bRT. No local failures were observed when EQD2>32.5 Gy was given. LC was improved with EQD2>20 Gy (24 mo LC: 94.5% vs 68.6%; p = 0.075). Following BRT, median overall decreases in MTV, SUVmax, SUVmean, and TLG were 22.2 cc (63.1%), 8.9 (36.8%), 3.4 (31.1%), and 297.9 cc (75.8%), respectively. Median decreases in MTV, SUVmax, SUVmean, and TLG in irradiated sites were 15.6 cc (91.1%), 17.0 (74.6%), 6.8 (55.3%), and 157.0 cc (94.6%), respectively. PFS was significantly improved in patients with reductions of MTV of at least 36 cc (24 mo PFS: 69.2% vs 0%; p = 0.047) or SUVmax of at least 15 (24-mo PFS: 80.0% vs 28.1%; p < 0.001). LC was significantly improved in lesions with reductions of SUVmax of at least 14 (24-mo LC: 100% vs 67.3%; p < 0.001) or SUVmean of at least 7 (24-mo LC: 100% vs 74.4%; p < 0.001).

CONCLUSION

bRT led to significant reductions in MTV, SUVmax, SUVmean, and TLG. The extent of these decreases correlated with improved PFS and LC. There appears to be a dose-response relationship. Larger cohorts should validate the value of interim PET following bRT, and associated changes in disease burden as a means of prognosticating patients. Future work might evaluate whether escalation of BT in patients with suboptimal response, using either systemic therapy or higher radiation doses, has an impact on outcomes.

Testosterone replacement ameliorates nonalcoholic fatty liver disease in castrated male rats

Nonalcoholic fatty liver disease is common in developed countries and is associated with obesity, metabolic syndrome, and type 2 diabetes. T deficiency is a risk factor for developing these metabolic deficiencies, but its role in hepatic steatosis has not been well studied. We investigated the effects of T on the pathogenesis of hepatic steatosis in rats fed a high-fat diet (HFD). Adult male rats were randomly placed into four groups and treated for 15 weeks: intact rats on regular chow diet (RCD), intact rats on liquid HFD (I+HFD), castrated rats on HFD (C+HFD), and castrated rats with T replacement on HFD (C+HFD+T). Fat contributed 71% energy to the HFD but only 16% of energy to the RCD. Serum T level was undetectable in castrated rats, and T replacement led to 2-fold higher mean serum T levels than in intact rats. C+HFD rats gained less weight but had higher percentage body fat than C+HFD+T. Severe micro- and macrovesicular fat accumulated in hepatocytes with multiple inflammatory foci in the livers of C+HFD. I+HFD and C+HFD+T hepatocytes demonstrated only mild to moderate microvesicular steatosis. T replacement attenuated HFD-induced hepatocyte apoptosis in castrated rats. Serum glucose and insulin levels were not increased with HFD in any group. Immunoblots showed that insulin-regulated proteins were not changed in any group. This study demonstrates that T deficiency may contribute to the severity of hepatic steatosis and T may play a protective role in hepatic steatosis and nonalcoholic fatty liver disease development without insulin resistance.