Orthovoltage radiation of normal canine nasal passages: assessment of depth dose.

Frozen heads of 9 clinically normal dogs were irradiated with orthovoltage x-rays. Surface doses and nasal cavity depth doses were measured, and the percentage of surface dose (depth dose) was calculated at random depths from the dorsal cutaneous surface in transverse planes through the medial and lateral canthi. Depth dose of 2 orthovoltage x-ray beams having half-value layers of 1.5 mm of Cu (96 keV) and 2.6 mm of Cu (134 keV) were compared with and found to resemble that reported in depth dose tables based on soft tissue equivalent material. Any differences (identified graphically) in depth dose, compared with that described using a uniform (soft tissue equivalent) phantom, were explained by the variations in tissue composition and the presence of air within the normal nasal and paranasal cavities.