Comparison of Calculated Radiation Delivery Versus Actual Radiation Delivery in Military Macaws (Ara militaris).

The skin and oral cavity are common sites of neoplasia in avian species. Radiation therapy has been described for the treatment of these tumors in birds; however, its observed effectiveness has been variable. One possible explanation for this variability when radiation is used to treat the head is the unique anatomy of the avian skull, which contains an elaborate set of sinuses not found in mammalian species. To compare a calculated dose of radiation intended to be administered and the actual amount of radiation delivered to the target area of the choana in 3 adult military macaws (Ara militaris), computed tomography scans were obtained and the monitor unit was calculated to deliver 100 cGy (1Gy) by using radiation planning software. The birds received 3-4 radiation treatments each from a megavoltage radiation therapy unit. A thermoluminescent dosimetry chip (TLD) placed in the choana of the birds was used to measure the amount of ionizing radiation delivered at each treatment. The TLDs were kept in place using Play-Doh as a tissue analog. The actual dose of radiation delivered was lower than the 100-cGy calculated dose, with the 95% confidence limits of predicted bias values between 2.35 and 5.39 (radiation dose from 94.61 to 97.65 cGy). A significant difference was identified between the actual amount of radiation delivered and the calculated radiation goal (P < .001). None of the TLDs received the intended dose of 100 cGy of radiation. The results revealed that the amount of radiation delivered did not reach intended levels. Because the combination of the significance of this discrepancy and the standard dose inhomogeneity could lead to greater than 10% dose inhomogeneity, future investigation is warranted for accurate dose calculation and efficacy of radiation therapy for neoplasia at the lumen of the choana in birds.