Program Information
EBT3 Gafchromic Film and NanoDot OSLDs as In-Vivo Dosimeters for Total-Skin Electron Therapy
J Cammin*, H Li , Washington University School of Medicine, St. Louis, MO
Presentations
TU-RPM-GePD-T-1 (Tuesday, August 1, 2017) 3:45 PM - 4:15 PM Room: Therapy ePoster Lounge
Purpose: To assess the usability of EBT3 Gafchromic film and NanoDot OSLDs as in-vivo dosimeters for total-skin electron therapy (TSET).
Methods: EBT3 film and OSLDs were used during commissioning of TSET to measure PDDs and surface dose for a stationary TSET technique with six dual-fields (gantry angles of 270+/-20°) using 6MeV high-dose rate electrons. An anthropomorphic phantom was placed at 320cm SSD behind a 1cm acrylic screen. Film was placed between two axial slabs of the phantom to measure PDD and on the surface (together with OSLDs) to measure skin dose. The film was scanned in color at least 24 hours after exposure. Both red and blue channel were used to convert optical density to dose. OSLDs were read using a calibration function from 6MV photon beams.
Results: The PDD from a single anterior dual-field and from six dual-fields at 60° angular increments using EBT3 film showed the expected behavior. The full TSET PDD had a dose maximum at the skin surface due to the contribution from oblique electron fields for each surface point. Repeated measurements of surface dose with different film pieces of the same batch gave consistent results within ± 4%. The surface dose reported by the OSLDs was systematically 4–10% lower than the measured film dose.
Conclusion: EBT3 film provides reliable in-vivo dosimetry for TSET if a strict protocol is followed. Calibration functions based on multiple color channels can compensate for intra and inter-film variations. OSLDs are easy to use for in-vivo dosimetry. However, OSLD readers are typically calibrated with 6 MV photons, and a dose-correction factor is required when using OSLDs for TSET dosimetry. This factor is attributed to the lower effective electron energy in TSET treatments (~2.1MeV) and a greater sensitivity of OSLDs to the incident beam angle.
Contact Email: