Kidney cancer would be unlikely in a 4-year old.
UTIs in children should be further evaluated for urine reflux. The scan that your physician is talking about is likely a voiding cystourethrogram (VCUG), which can detect this abnormality.
If negative, imaging the kidneys with a CT scan or ultrasound can be considered to rule out intrinsic kidney disease.
These options can be discussed with your personal physician.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
kevinmd_