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Scatter distribution & shielding geometry around patient/staff

Side view of a fluoroscopy table. An under-couch x-ray tube directs the primary beam up through the patient to the image receptor. The patient is the main source of Compton scatter. Nested isodose arcs show scatter falling with distance from the patient by the inverse-square law, labelled 0.5 m times 4, 1 m times 1, 1.5 m times 0.4, and 2 m times 0.25. Scatter is greater on the entrance (tube) side than the exit (detector) side. An operator stands back at about 2 m wearing a 0.25 mm lead apron. Notes state that patient scatter dominates staff dose over design-limited tube leakage, and that a 0.25 mm lead apron attenuates scatter about 10 to 20 times and protects against scatter, not the primary beam.

Scatter shielding geometry in a fluoroscopy suite Side view of a fluoroscopy table. An under-couch x-ray tube directs the primary beam up through the patient to the image receptor. The patient is the main source of Compton scatter. Nested isodose arcs show scatter falling with distance from the patient by the inverse-square law, labelled 0.5 m times 4, 1 m times 1, 1.5 m times 0.4, and 2 m times 0.25. Scatter is greater on the entrance (tube) side than the exit (detector) side. An operator stands back at about 2 m wearing a 0.25 mm lead apron. Notes state that patient scatter dominates staff dose over design-limited tube leakage, and that a 0.25 mm lead apron attenuates scatter about 10 to 20 times and protects against scatter, not the primary beam. Scatter geometry in a fluoroscopy suite (side view) image receptor (detector) patient — main scatter source x-ray tube (under couch) primary beam exit (detector) side: less scatter entrance (tube) side: more scatter 0.5 m · ×4 1 m · ×1 1.5 m · ×0.4 2 m · ×0.25 isodose contours greater distance → lower dose (∝ 1/r²) operator lead apron ~0.25 mm Pb (scatter protection) Patient Compton scatter dominates staff dose. Tube-housing leakage is design-limited (≤1 mGy/h at 1 m) and minor. Scatter at 1 m ≈0.1–0.5% of entrance dose rate; it falls as 1/r². Tighter collimation (smaller field) → less scatter. A 0.25 mm Pb apron attenuates scatter ~10–20× — it protects against scatter, not the primary beam.
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