Dose-volume complication analysis for visual pathway structures of patients with advanced paranasal sinus tumors

Abstract

Purpose : The purpose of the present work was to relate dose and volume information to complication data for visual pathway structures in patients with advanced paranasal sinus tumors. Methods and Materials : Three-dimensional (3D) dose distributions for chiasm, optic nerve, and retina were calculated and analyzed for 20 patients with advanced paranasal sinus malignant tmors. 3D treatment planning with beam's eye view capability was used to design beam and block arrangemeents, striving to spare the contralateral orbit (to lessen the chance of unilateral blindness) and frequently the ipsilateral orbit (to help prevent bilateral blindness). Point doses, dose-volume histogram analysis, and normal tissue complciation probability (NTCP) calculations were performed. Published tolerance doses that indicate significant risk of complications were used as guidelines for analysis of the 3D dose distributions. Results : Point doses, percent volume exceeding a specified published tolerance dose, and NTCP calculations are given in detail for patients with complications versus patients without complications. Two optic nerves receiving maximum doses below the published tolerance dose sustained damage (mild vision loss). Three patients (of 13) without optic nerve sparing and/or chiasm sparing had moderate or severe vision loss. Complication data, including individual patient analysis to estimate the overall risk for loss of vision, are given. Conclusion : 3D treatment planning techniques were used successfully to provide bilateral sparing of the globe for most patients. It was more difficult to spare the optic nerves, especially on the ipsilateral side, when prescription dose exceeded the normal tissue tolerance doses. NTCP calculations may be useful in assessing complication risk better than point dose tolerance criteria for the chiasm, optic nerve, and retina. It is important to assess the overall risk of blindness for the patient in addition to the risk for individual visual pathway structures.