Skin exposure and thyroid dose distribution using niobium filtration.

A thermoluminescent dosimetry system was utilized to investigate how much the radiation dose is reduced through the addition of a niobium-based accessory filter to an X-ray unit's conventional aluminum filter. A two-bitewing series was exposed in a tissue-equivalent human phantom. The skin exposures from an X-ray beam with the added niobium filter and a beam with the aluminum filter alone were measured and compared. Thyroid dose distribution was also measured and similarly compared. Utilization of the niobium filter resulted in a significant reduction in skin exposure (p less than 0.001) of 14.8 per cent. Thyroid dose was not lessened by using the niobium filter, however. In fact, in one region of the thyroid it increased significantly.