Dose distribution resulting from changes in aeration of nasal cavity or paranasal sinus cancer in the proton therapy

Background and purposeAeration in the nasal cavity and paranasal sinus (NCPS) was investigated during the course of proton therapy (PT), and the influence of aeration on the dose distribution was determined.Material and methodsTwenty patients with NCPS cancer (10 nasal cavity, 10 paranasal sinus) were analyzed. All the patients received a total proton beam irradiation dose of 38–78.4 Gray equivalents (GyE). Two to five CT examinations were performed during the course of treatment. The aeration ratio inside the cavity/sinus was calculated for each CT observation. Moreover, a simulation study supposing that the first treatment plan had been continued until the end of treatment was performed using the subsequent CT findings.ResultsThe aeration ratio was increased in 18 patients. The largest increase was from 15% to 82%. Three patients had a simulated maximum cumulative dose in the brainstem of beyond 60 GyE, while 10 patients had a simulated maximum cumulative dose in the optic chiasm of beyond 50 GyE. The shortest simulated time period to reach the dose limitation was 21 days.ConclusionsAeration in the NCPS is altered during the course of PT treatment and can greatly alter the dose distribution in the brainstem and optic chiasm