I apologize for not posting it in the first place.

Ul Haque M, Shufflebarger HL, O'Brien M, Macagno A. Radiation exposure during pedicle screw placement in adolescent idiopathic scoliosis: is fluoroscopy safe?. Spine 2006;1;31(21):2516-20.

I know about it from here: https://www.nuvasive.com/solutions/lessray/