Bi-lateral 3 view knee x-ray

If I do a bi-lateral 3 view knee x-ray, I have always used the code 73562 twice with the lt/rt modifiers. A doctor is claiming that it should be billed as 73564 once to cover both knees. According to my billers, they have never had a rejection when I bill 73562 x 2....so am I right or is the doctor right?