Reconstruction of high-resolution 3D dose from matrix measurements: error detection capability of the COMPASS correction kernel method

The COMPASS system (IBADosimetry) is a quality assurance (QA) tool which reconstructs 3D doses inside a phantom or a patient CT. The dose is predicted according to the RT plan with a correction derived from 2D measurements of a matrix detector. This correction method is necessary since a direct reconstruction of the fluence with a high resolution is not possible because of the limited resolution of the matrix used, but it comes with a blurring of the dosewhich creates inaccuracies in the dose reconstruction. This paper describes the method and verifies its capability to detect errors in the positioning of a MLC with 10 mm leaf width in a phantom geometry. Dose reconstruction was performed forMLC position errors of various sizes at various locations for both rectangular and intensity-modulated radiotherapy (IMRT) fields and compared to a reference dose. It was found that the accuracy with which an error inMLC position is detected depends on the location of the error relative to the detectors in the matrix. The reconstructed dose in an individual rectangular field for leaf positioning errors up to 5 mm was correct within 5% in 50% of the locations. At the remaining locations, the reconstruction of leaf position errors larger than 3 mm can show inaccuracies, even though these errors were detectable in the dose reconstruction. Errors larger than 9 mm created inaccuracies up to 17% in a small area close to the penumbra. The QA capability of the system was tested through gamma evaluation. Our results indicate that themean gamma provided by the system is slightly increased and that the number of points above gamma 1 ensures error detection for QA purposes. Overall, the correction kernel method used by the COMPASS system is adequate to perform QA of IMRT treatment plans with a regular MLC, despite local inaccuracies in the dose reconstruction

Applicability of the Matrixx detector combined with the compass system to detect leaf positioning errors of an elekta beam modulator

This study explores the capability of the COMPASS system (IBA Dosimetry, Germany) to detect leaf positioning errors of a high resolution MLC with 4mm leaf width using a lower resolution (7.62mm detector spacing) 2D matrix of ionisation chamber

An efficient and independent 3D dose calculationtool for quality assurance of complex radiotherapy treatment plans

To validate the model-based 3D dose calculation performed by the COMPASS system, and to evaluate the use of the combination of model-based and measurement-based 3D dose determination for clinical QA purposes

Reconstruction of high-resolution 3D dose from matrix measurements: error detection capability of the COMPASS correction kernel method

To quantify the dosimetric accuracy of the COMPASS correction kernel method, and to determine its ability to detect dose delivery errors caused by MLC leaf mis-positioning

An efficient and independent 3D dose calculationtool for quality assurance of complex radiotherapy treatment plans

To validate the model-based 3D dose calculation performed by the COMPASS system, and to evaluate the use of the combination of model-based and measurement-based 3D dose determination for clinical QA purposes