Characterization and clinical evaluation of a novel 2D detector array for conventional and flattening filter free (FFF) IMRT pre-treatment verification

Abstract

Background and purposeThe novel MatriXXFFF (IBA Dosimetry, Germany) detector is a new 2D ionization chamber detector array designed for patient specific IMRT-plan verification including flattening-filter-free (FFF) beams. This study provides a detailed analysis of the characterization and clinical evaluation of the new detector array. Material and methodsThe verification of the MatriXXFFF was subdivided into (i) physical dosimetric tests including dose linearity, dose rate dependency and output factor measurements and (ii) patient specific IMRT pre-treatment plan verifications. The MatriXXFFF measurements were compared to the calculated dose distribution of a commissioned treatment planning system by gamma index and dose difference evaluations for 18 IMRT-sequences. All IMRT-sequences were measured with original gantry angles and with collapsing all beams to 0° gantry angle to exclude the influence of the detector's angle dependency. ResultsThe MatriXXFFF was found to be linear and dose rate independent for all investigated modalities (deviations ≤0.6%). Furthermore, the output measurements of the MatriXXFFF were in very good agreement to reference measurements (deviations ≤1.8%). For the clinical evaluation an average pixel passing rate for γ(3%,3mm) of (98.5±1.5)% was achieved when applying a gantry angle correction. Also, with collapsing all beams to 0° gantry angle an excellent agreement to the calculated dose distribution was observed (γ(3%,3mm)=(99.1±1.1)%). ConclusionsThe MatriXXFFF fulfills all physical requirements in terms of dosimetric accuracy. Furthermore, the evaluation of the IMRT-plan measurements showed that the detector particularly together with the gantry angle correction is a reliable device for IMRT-plan verification including FFF.