Patient-specific online dose verification based on transmission detector measurements

Abstract

Background and purpose: Since IMRT-techniques lead to an increasingly complicated environment, a patient specific IMRT-plan verification is recommended. Furthermore, verifications during patient irradiation and 3D dose reconstruction have the potential to improve treatment delivery, accuracy and safety. This study provides a detailed investigation of the new transmission detector (DTD) Dolphin (IBA Dosimetry, Germany) for online dosimetry.

Materials and methods: The clinical performance of the DTD was tested by dosimetric plan verification in 2D and 3D for 18 IMRT-sequences. In 2D, DTD measurements were compared to a pre-treatment verification method and a treatment planning system by gamma index and dose difference evaluations. In 3D, dose-volume-histogram (DVH) indices and gamma analysis were evaluated. Furthermore, the error detection ability was tested with leaf position uncertainties and deviations in the linear accelerator (LINAC) output.

Results: The DTD measurements were in excellent agreement to reference measurements in both 2D (γ3%,3mm=(99.7±0.6)% <1, ΔD±5%=(99.5±0.5)%) and 3D. Only a small dose underestimation (<2%) within the target volume was observed when analyzing DVH-indices. Positional errors of the leaf banks larger than 1mm and errors in LINAC output larger than 2% were identified with the DTD.

Conclusions: The DTD measures the delivered dose with sufficient accuracy and is therefore suitable for clinical routine.

Keywords: Online dose verification; Quality assurance; Transmission detector.