During a prolonged fluoroscopic GI procedure the radiologist asks about skin injury risk, with the table height changed twice and steep obliques used. The dose-area product is moderate but fluoroscopy time is long. Which dose-monitoring parameter best estimates deterministic skin risk in this setting?

Cumulative air kerma at the patient entrance reference point is the standardized surrogate for peak entrance skin dose and deterministic injury, integrating output, pulse parameters, filtration and duration at a fixed gantry-based point so thresholds for erythema can be applied even when dose-area product is moderate but overlapping steep obliques concentrate dose on one skin area. The DAP-based approach fails because dose-area product measures total energy and stochastic burden, and identical DAP distributed widely versus focused on a single overlapping port produces very different peak skin doses after table moves. The time-based approach fails because fluoroscopy time omits dose rate, habitus, magnification, frame rate and automatic exposure response, so long low-rate screening may be safe while brief high-rate acquisition injures skin. The isocenter kerma approach fails because isocenter calibration diverges from skin entrance exposure when table height changes source-to-skin distance under inverse-square conditions despite using the correct quantity. An exam caveat is that the reference point is not the true skin location, so with changed table height and obliques formal peak-dose mapping is required when action levels are approached. As a practical check record displayed cumulative air kerma, angulations and table shifts, compare to the 3 Gy follow-up level, and arrange skin surveillance and documentation.