Serial magnetic resonance imaging (MRI) scans. (A) Taken at the initial diagnosis. The red arrow indicates 7.3 × 4-cm mass on the right posterior-lateral abdominal wall at the level of the flank and right kidney. (B) Taken after the initial surgery, showing no evidence of disease. (C) Taken 12 months after the initial surgery. The red arrow indicates 6.5 × 2.8-cm recurrent mass on the previous surgical bed. (D) Taken at 24 months after completing proton therapy. No evidence of re-recurrence of the tumor.