We measured radiation doses to the thyroid during neurointerventional angiographic procedures to assess the effectiveness of lead shields at dose reduction.
METHOD AND MATERIALS
Fifty patients were recruited from those attending for endovascular treatment of AVMs and aneurysms. Informed consent was obtained and patients were randomised into one of 2 groups A) No shield(n=25) B) Thyroid lead shield(n=25). Two thermoluminescent dosimeters(TLDs) were placed over the thyroid gland to measure dose in each patient. A thyroid lead shield(Pb eq. 0.5 mm) was placed around the neck of patients in group B after the neurointerventional radiologist had obtained satisfactory working access above the neck. The total Dose-Area-Product(DAP) value, number and type of digital subtraction angiography(DSA) runs and screening time were recorded for all patients.
Patient demographics included: age(mean 49.5 yrs., range:15-73yrs.), M:F=2:1. No statistically significant differences were seen between the 2 groups for age or sex. Twice as many anterior circulation compared to posterior circulation procedures were performed. The mean screening time was 27.35 minutes, mean DAP value: 13,908 cGy/cm² (approx. 12 mSv). The average number of DSA runs was 14. As screening time, number of DSA runs and projections varied between patients, we calculated the average thyroid dose and divided by the DAP value for each patient, to compare relative doses between the 2 groups. This revealed a statistically significant difference between the 2 groups: mean relative dose 6.68(unshielded) vs. 3.41(shielded)[p=0.039], a dose reduction of 49% with thyroid shileds. Four patients were excluded from the study when the thyroid shield interfered with the working angle.
Considerable radiation exposure to the thyroid is incurred during neurointerventional procedures, as a consequence of long screening times and multiple DSA runs. This highlights the need for increased awareness of patient radiation protection. Young patients regularly attend for these procedures, often repeatedly. Patient thyroid lead shielding yields significant radiation protection, is inexpensive and when not obscuring the field of view, should be used routinely.