Magnetic resonance imaging response in patients treated with definitive radiation therapy for medically inoperable endometrial cancer—Does it predict treatment response?

Abstract

Purpose: Many patients with endometrial cancer cannot undergo surgery and instead receive definitive radiation therapy (RT). We investigate the correlation between MRI response to RT and clinical outcomes. Methods and Materials: Women with inoperable, clinical Stage I endometrial cancer were treated with definitive brachytherapy (BT) with/without pelvic RT (PRT). Patients underwent MRI with functional diffusion-weighted imaging before and after RT. A radiologist retrospectively classified cases as complete, partial, or indeterminate response (CR, PR, or IR, respectively) vs. disease progression. Local control was clinicopathologically defined. Results: From 2007 to 2017, 50 women underwent definitive RT. Thirty-five (70%) received BT alone (median dose 37.5 Gy). For combined therapy, the median PRT and BT doses were 45 and 25 Gy, respectively. Median gross tumor volume and high-risk clinical target volume were 7.1 cc and 90.0 cc, respectively. Median followup among living patients was 20 months. All patients underwent post-RT MRI with T1/T2 sequencing at a median of 3.2 months after RT; 40 patients (80%) underwent functional diffusion-weighted imaging sequences. On initial post-RT MRI, CR was documented in 42 patients (84%), IR in 1 patient (2%), and PR in seven patients (14%). At median followup of 16.3 months, no CR patients had uterine failure. Among eight patients with initial PR/IR, all were found to be clinicopathologically no evidence of disease at the uterus on further evaluation. Conclusions: Definitive RT with BT or BT + PRT is associated with high response rates on MRI. Overall, initial CR predicted for excellent outcome with no infield failure.