SU-E-T-491: Accuracy of Dose Calculation in Inhomogeneity Region for Proton Radiotherapy

Abstract

Purpose: The purpose of this study was to evaluate the accuracy of dose calculation in inhomogeneity region provided with Eclipse treatment planning system for proton therapy using the head and neck phantom. Method and Materials: The inhomogenous head and neck phantom for proton therapy quality assurance (QA) was housed in a custom-designed package for efficient evaluation of the measured doses using the different materials and various dosimeters (pinpoint type ionization chamber, TLD- 100, glass dosimeter). All measurements were performed in clinical proton beam at National Cancer Center in Korea. The accuracy of proton therapy dose calculations with pencil-beam algorithms (Varian Eclipse) were also investigated with respect to measurements used in head and neck phantom in the presence of inhomogeneity region (PMMA, air, bony structure). Results: The differences for pencil-beam dose calculation algorithm and measured dose with dosimeters were 3.0% in average target doses (PMMA region). However, the measured results with dosimeters were approximately 7.0% higher than the calculated dose by Eclipse in air region. Conclusion: Our results show that accurate measurements of the inhomogeneity region improve the accuracy of the dose calculation algorithms predicted by the treatment planning system.