Physical and technical quality assurance in the CHARTWEL-Bronchus trial.

Abstract

On-site physical quality assurance (QA) was performed in the participating centers of the CHARTWEL-Bronchus trial to ensure that physical and technical treatment parameters correspond with the requirements of this trial. Questionnaires were sent to the clinics to obtain information on the equipment and in-house QA policies. In addition, two phantoms with drillings for an ionization chamber were shipped with detailed instructions for CT-based treatment planning of a fixed field (RW3 phantom) and a standardized isocentric 3-field technique (Rando humanoid phantom). Using their routine treatment planning system, the participating centers performed point dose calculations for the isocenters in both phantoms and for defined points in the lungs and the spinal cord of the Rando phantom. During the on-site visit, the doses in these points and the deviation of the actual monitor calibration from the internal reference value of the department were determined. In addition, relevant geometric parameters of the accelerator were checked. In the RW3 phantom, the maximum dose deviations from the prescribed value were 3.5% without correction for the actual monitor calibration and 2.1% after correction. The maximum dose deviation in the isocenter of the Rando phantom was 4.0%. To separate the influence of the treatment planning system on this deviation from other sources, all measurements in the Rando phantom were corrected for the deviations determined in the RW3 phantom. After this correction, the maximum deviation was 3.0% in the isocenter. For the other measurement points, the largest dose deviation of 7% was found in the left lung. Deviations of geometric parameters were negligible in all audited departments. The CHARTWEL-Bronchus physical QA program revealed a high conformity of geometric and dosimetric parameters and valid dose calculations by the CT-based treatment planning systems in all audited departments.