SU-E-J-125: Uncertainty in Accumulated Dose to the Cochlea Due to Setup Error during External Beam Treatment of Head & Neck Cancer Patients

Medical Physics
M YanA Jackson

Abstract

Treatment uncertainties are not included in modeling dose response of hearing loss. We determine uncertainty of accumulated dose to cochleas of head & neck cancer patients due to setup error during treatments of external beam IMRT. We studied 8 patients: 1 planning CT for each patient and total 40 cone beam CTs. Those patients were treated with 33 fractions. Treatments delivered 70 Gy to PTV, 50 to 60 Gy to nodal and sub-clinical disease using IMRT dose painting. Setup error was measured using 6-dimensional rigid registration between planning CT and cone beam scans obtained prior to treatment. Planning CTs were transformed and resliced to produce 'treatment CTs' according to the measured setup error matrix to simulate the cochlea position during treatment. We calculated dose delivered to cochleas at each treatment position. Treated dose to the cochlea from each fraction was accumulated on the planning CT using its registration with each 'treatment CT'. The RMS value of set error of left cochlea is 0.48pm0.28cm, right cochlea is 0.47pm0.26cm. Mean values of left and right cochleas are ∼zero. Uncertainty in the dose to cochlea depends on each treatment plan and relative positions of the cochlea and target volumes. Average uncerta...Continue Reading

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