4.6 Gy Air Kerma, Right Radial Access and a Shield Moved Aside

Start with magnitude: 4.6 Gy cumulative air kerma is well past the 2 Gy notification level and approaching the range where deterministic skin effects become a real possibility - this is a case that should have been dose-managed from minute one, not at the end.

Contributors, roughly in order of impact:

• Detector at maximum distance: in a C-arm, moving the detector away from the patient means the patient sits closer to the source. Entrance skin dose rises steeply as source-skin distance falls. This is a large, easily reversible factor.
• Table kept high for ergonomics: same effect - it lowers the patient relative to the tube.
• Magnification in LAO cranial for most wire work: magnification roughly doubles dose and narrows the beam onto the same skin area, compounding the local peak.
• 15 pulses/s fluoroscopy throughout: halving to 7.5 pulses/s is usually adequate for wire work and cuts fluoro dose substantially.
• Long fluoroscopy time with a fixed beam angle: concentrating dose on one skin site is what produces injury.

Changes: detector down to the patient, lower the table, get out of magnification except when required, drop pulse rate, collimate tightly, use last-image hold, and change the beam angle periodically so dose is spread over different skin.

Because a deterministic threshold may have been reached, documentation and follow-up are part of the procedure, not optional extras:

• Record the cumulative air kerma (4.6 Gy) and DAP in the procedure report and the patient record, along with beam angulations used and total fluoroscopy time.
• Notify the patient that a higher radiation dose was used and what to watch for.
• Arrange a skin examination at roughly 2-4 weeks: erythema, blistering or a defined area of hair loss in the beam entry region. Early changes may be delayed and subtle.
• Flag the record so any future procedure takes the prior dose into account - cumulative skin dose is additive over weeks to months.
• Escalate to a radiation safety officer or physicist if the peak skin dose estimate (accounting for magnification and angulation, not just the displayed air kerma) is judged to exceed institutional action levels.

The judgment point: air kerma is a system reference point, not the skin dose itself; angulation, magnification and table position all concentrate it, so the clinical estimate should err on the high side.

Two separate effects, both fixable:

Position relative to the beam. With right radial access the operator works at the patient's right arm. During LAO projections the tube is on the patient's right side, so the operator is on the x-ray entrance side, where scatter is greatest. During RAO the geometry reverses and the same operator is on the detector side, with much lower exposure. Because LAO cranial is used heavily here, the operator's exposure is concentrated on the worst projections.

Removed shielding. Moving the ceiling-suspended shield aside removes the single most effective staff protection. The table-mounted lead drape and the ceiling shield together provide most of the attenuation; lead apron alone leaves the head, neck and lens exposed.

Corrections:

1. Put the ceiling shield back, positioned between the operator's head/neck and the patient's right side.
2. Keep the table drape in place; do not let it be lifted for access.
3. Step back during cine and any long fluoroscopy runs, and increase distance whenever hands are off the patient.
4. Wear a second dosimeter at collar level if lens dose is a concern, and review collar doses after high-fluoroscopy cases.
5. Keep the detector as close as possible - lower scatter production benefits staff as much as the patient.