Monte Carlo evaluation of tissue inhomogeneity effects in the treatment of the head and neck

摘要: Abstract Purpose: To use Monte Carlo dose calculation to assess the degree which tissue inhomogeneities in head and neck affect static field conformal, computed tomography (CT)-based 6-MV photon treatment plans. Methods Materials: We retrospectively studied three-dimensional plans that had been used for of 5 patients with tumors nasopharyngeal or paranasal sinus regions. Two large surgical cavities. The were designed a clinical planning system uses measurement-based pencil-beam dose-calculation algorithm an equivalent path-length inhomogeneity correction. Each plan employs conformally-shaped beams. Patient anatomy electron densities obtained from CT images. For each plan, distribution was recalculated method, utilizing same beam geometry method accurately accounts perturbation effects local heterogeneities. calculated distributions compared those system. Results: affects individual fields varies specific anatomic geometry, especially size location air cavities relation orientation size. Most apertures completely enclose within adjacent gross tumor volume (GTV). Equivalent squares (including blocking) ranged approximately 9.5 cm. A common feature observed is doses directly behind cavity are lower. However, after combining employed overall shows only small differences between two methods. all patients, showed slightly lower received by 95% target (D 95 ) than algorithm. average difference encompassed prescription isodose line less 2.2%. dose-volume histograms (DVHs) GTV generally small. brainstem chiasm, DVHs similar. spinal cord, details DHV 1 cc 1cc structure observed, predicting increased indices cord. these changes not expected be clinically significant. Conclusion: photons, both normal on coverage adequately accounted conventional pencil methods cases studied. Although structures depending whether calculation, In general, corrected primary attenuation pathlength sufficiently accurate head-and-neck using photons.