Evaluation of dose profiles using Gafchromic EBT3 films in Leksell Gamma Knife 4C around inhomogeneities in the treatment of pituitary adenoma in anthropomorphic heterogeneous head phantom

Purpose: The Leksell Gamma Knife is a complete system for radiosurgery. Treatment dose planning of Gamma Knife assumes the human head as a homogenous media; thus received dose by target tissue and organs at risk may be lower or higher than predicted dose. Our main interest is to compare measured dose profiles in an anthropomorphic heterogeneous head phantom by EBT3 films with calculated dose by Leksell Gamma Plan. Methods: An adult head phantom with size, shape and inhomogeneity the same as an adult human head was constructed. Then dose profiles across from isocenter and organs at risk were measured by EBT3 films and compared with those predicted by Leksell Gamma Plan. Results: Our findings indicate that when isocenter placed at the target tissue near the frontal sinus cavity, overestimation and underestimation of the dose value affect the dose profiles. In some points of organs at risk, measured dose is more than calculated dose. Comparison of isodose curves near air-tissue interface shows that in higher isodose levels, dose perturbation is more seen. Distance to Agreement parameter for some isodose lines exceeds the total positioning error for Gamma Knife ( +/- 2 mm). Also dose differences are more than numerical accuracy in dose delivery for stereotactic radiosurgery ( +/- 5%). Conclusions: Inhomogeneities in head impress dose distributions. Ignorance of inhomogeneities can cause the parts of target tissue receive under dosage and also in some points, organs at risk receive more dose. Results of this study are closer to reality because of anthropomorphic heterogeneous head phantom.