Optimization of Patient Skin Dose by C-Arm Angulation in Interventional Radiology for Spinal Vascular Lesions

Accurate assessment of a patient's skin dose during interventional radiology (IVR) for spinal vascular lesions is challenging, particularly when the upper arms are positioned within the irradiation field. This study aimed to quantify the discrepancy between system-displayed dose values and actual skin dose, while assessing the impact of C-arm angulation on patient skin dose during spinal IVR.

Dosimetric measurements were performed using an adult anthropomorphic phantom. A 0.6-cc CT ionization chamber was positioned on the phantom surface at the center of the lateral C-arm irradiation field. Fluoroscopic irradiation was performed for 1 min at right anterior oblique (RAO) angulations ranging from 40° to 120° in 10° increments using a biplane angiography system. The measured skin dose was compared against the system-displayed reference air kerma at the patient reference point. Measurements were performed in triplicate and evaluated across 3 anatomical regions: the upper thoracic region (including the upper arms), lower thoracic region (excluding the upper arms), and lumbar region. Air kerma was used as a surrogate for skin dose.

The measured skin dose exceeded the system-displayed dose in all anatomical regions, with the most significant discrepancy observed in the upper thoracic region. At RAO 90°, which corresponds to a true lateral projection, the measured skin dose in the upper thoracic region was 1.68 times higher than the system-displayed dose. Conversely, smaller discrepancies were observed in the lower thoracic and lumbar regions, and the measured doses were 1.17 and 1.18 times higher than the displayed values, respectively. Modifying the C-arm angulation by 20° from RAO 90° significantly reduced the measured skin dose in the upper thoracic region, with reductions of 77.9% and 85.4% at RAO 70° and 110°, respectively. However, even with these optimizations, the measured skin dose remained 1.42 times higher than the system-displayed dose.

During spinal IVR, particularly in the lateral projections of the upper thoracic spine, system-displayed dose may substantially underestimate actual patient skin dose when the upper arms are included within the irradiation field. This discrepancy likely reflects increased X-ray tube output driven by automatic dose control in response to elevated tissue attenuation. Optimizing the C-arm angulation represents a practical and effective strategy for reducing patient skin dose in this anatomically challenging region.