Patient and Aneurysm Characteristics (table 1 and table 2)

• 183 patients (68.3% female), mean age 62.0 ± 12.8 years.
• 155 aneurysms (79.4%) in the anterior circulation; 40 (20.6%) in the posterior circulation.
• 171 patients (90.0%) had a single aneurysm; 12 had multiple.
• Intracranial stents such as neck-bridge stent for coil embolization and flow diverter stent were used in 106 patients (57.9%).

Radiation Dose Parameters (table 1)

• Mean TFT: 44.2 ± 23.1 min
• Mean K_a,r: 2.17 ± 1.18 Gy
• Mean P_KA: 153.8 ± 103.2 Gy·cm²
• Mean K_a,r ratio: 1.92 ± 0.64
• Mean PSD: 0.96 ± 0.52 Gy

Table 1: Patient demographics, aneurysm characteristics and radiation dose characteristics. Ka,r ratio = Ka,r of frontal X-ray tube tube / Ka,r of lateral X-ray tube

PSD Location (figure 5)

PSD location distribution:

• Occipital region: 129 cases (70.5%)
• Temporal region: 54 cases (29.5%)

Fig 5: Breakdown of PSD location in NET. The PSD was located in the occipital region in 129 cases (70.5%) and the temporal region in 54 cases (29.5%).

Predictive Factors for Occipital PSD (table 2)

 Univariate analysis:

• Male sex: odds ratio [OR] = 2.24; 95% confidence interval [CI], 1.08−4.95; p = 0.0289
• Posterior circulation aneurysm: OR = 3.20; 95% CI, 1.27−9.82; p = 0.0123
• K_a,r ratio > 1.6: OR = 4.06; 95% CI, 2.04−8.21; p < 0.001

Multivariate analysis:

• Non-stent use: OR = 2.56; 95% CI, 1.22−5.65; p = 0.0125
• K_a,r ratio > 1.6: OR = 5.05; 95% CI, 2.39−11.1; p < 0.0001

These two parameters were the strongest independent predictors of occipital PSD.

Table 2: Univariate and multivariate analyses of PSD location. Univariate logistic analysis showed that male sex, posterior circulation aneurysm and Ka,r ratio > 1.6 were significantly associated with the occipital PSD. Multivariate logistic analysis showed that the non-stent use and ka,r ratio > 1.6 remained independent, significant predictors for the PSD occurring in the occipital region.

Representative case (figure 6)

A man in his 60s with an unruptured basilar tip aneurysm underwent coil embolization using a double-catheter technique without intracranial stent. The K_a,r was 2.63 mGy for the frontal X-ray tube and 0.79 mGy for the lateral X-ray tube. The resulting K_a,r ratio was 3.32, exceeding the threshold value of 1.6. The PSD was observed in the occipital region (No. 27), with a measured dose of 1.74 mGy.

Fig 6: Representative case of occipital PSD in a non-stent NET procedure. The Ka,r ratio was 3.32 (over 1.6), and the PSD was observed at the occipital region (No. 27). (A) Three-dimentional rotation angiography image (B) DSA image (working projection): pre embolization (C) DSA image (working projection): post embolization (D) Non-DSA image (working projection): post embolization (D): Skin dose distribution map obtained from direct measurement system. PSD was located in occipital region (No. 27)