SU-E-T-286: Verification of Treatment Delivery Monitor Unit (MU) Calculation and Dose Estimation of Bilateral Total Body Irradiation (TBI)

Medical Physics
S LiC Lin

Abstract

TBI treatment delivery MU and patient dose estimation are calculated manually at our institution. This study was to verify the accuracyof MU calculation and dose estimation of bilateral TBI by application of tissue heterogeneity correction. Twelve TBI patients were simulated from neck to thigh in bilateral TBI position. CT images were imported into the treatment planning system (Philips, Pinnacle3). Treatment dose was prescribed to the midpoint at the level of the umbilicus. Treatment distance was 519 cm. Both 6MV and 23 MV opposite lateral beams delivered 200 cGy to the dose prescription point with a 40 ×40 cm(2) field size and 45o collimator angle. A 1 cm thick spoiler was placed about 15 cm from patient skin. Adaptive convolution superposition with and without heterogeneity correction was used for calculation of MUs and doses at the midpoints of the shoulder, chest, abdomen, and pelvis. Monitor units calculated with heterogeneity correction were 1.1% and 0.9% smaller on average than those without heterogeneity correction for 6MV and 23MV beams respectively. The maximum deviations of MU were 3.8% and 2.8% smaller. Average percentage differences of point doses with and without heterogeneity corrections were -0.2%, 17.0%, -0.3%...Continue Reading

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