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Angular Dependence of Surface Dose Enhancement Measured On Several Inhomogeneities Using Radiochromic EBT3 Films

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A Jansen

A Jansen1,2*, A Schoenfeld1,2, D Poppinga1,2 , N Chofor 1,2 ,B Poppe1,2 , (1) University of Oldenburg, Oldenburg, Germany, (2) Pius Hospital Oldenburg, Oldenburg, Germany


SU-E-T-44 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: The quantification of the relative surface dose enhancement in dependence on the angle of incidence and the atomic number Z of the surface material.

Methods: Experiments were performed with slabs made of aluminum, titanium, copper, silver, dental gold and lead. The metal slabs with equal sizes of 1.0x8.0x8.8mm³ were embedded in an Octavius 4D phantom (PTW Freiburg, Germany). Radiochromic EBT3 films were used to measure the surface dose for angles of incidence ranging from 0° to 90°. The setup with the metals slabs at the isocenter was irradiated with acceleration voltages of 6MV and 10MV. Water reference measurements were taken under equal conditions.

Results: The surface dose enhancement is highest for angles of incidence below 30° and drops significantly for higher. The surface dose enhancement produced by lead and dental gold at 6MV showed a peak of 65%. At 90°, the surface dose enhancement dropped to 15% for both materials. The surface dose enhancements for silver, copper, titanium and aluminum were 45%, 32%, 22% and 12% at 0°, respectively. At an angle of incidence of 80°, the values dropped to 22%, 18%, 12% und 6%. The values for 10MV were very similar. Lead and dental gold showed peaks of 65% und 60%. Their values dropped to 18% at an angle of 90°. The surface dose enhancements for silver, copper, titanium and aluminum were 45%, 30%, 20% and 8% at 0°. At 80° the values dropped to 30%, 20%, 12% and 5%. A dependence of the magnitude of the surface dose enhancement on the atomic number of the surface material can be seen, which is in consistence with literature.

Conclusion: The results show that the surface dose enhancements near implant materials with high Z-values should be taken into consideration in radio therapy, even when the angle of incidence is flat.

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