135 Patient specific QA system: Experimental stress analysis by introducing intentional errors. (December 2018)

• Record Type: Journal Article
• Authors: Martinucci, E.; Capomolla, C.; Rosica, F.; Zagari, A.; Quarta, S.; De Luca, D.; Carlà, A.; Cazzato, M.
• Is Part Of: Physica medica. Volume 56(2018)Supplement 2
• Page Start: 147
• Page End: 148
• Publication Date: 2018-12
• Subjects: Medical physics -- Periodicals; Biophysics -- Periodicals; Biophysics -- Periodicals; Imagerie médicale -- Périodiques; Radiothérapie -- Périodiques; Rayons X -- Sécurité -- Mesures -- Périodiques; Physique -- Périodiques; Médecine -- Périodiques; 610.153
• DOI: 10.1016/j.ejmp.2018.04.146
• Languages: English
• ISSNs: 1120-1797

Abstract

Abstract: Purpose: QA procedures and their results are strictly connected to the measuring system. The purpose of this study is to investigate the sensitivity of Delta4 Phantom+ (Scandidos, 2015), by introducing intentional errors in some reference plans. It would be possible to evaluate the Delta4 ability to find errors related to the radiotherapy treatment. Methods: Delta4 Phantom+ consists of two orthogonal detector arrays placed in a 3D cylindrical PMMA phantom. Three VMAT reference plans were created in treatment planning system (Monaco, Version 5.11) and measured with Delta4 Phantom+. Reference plans are characterized by a simple geometry and involve anatomic parts such as prostate, head and neck and brain (stereotactic). The same plans were measured introducing errors during delivery. Errors introduced are: Monitor Unit variation (3%), collimator rotation by 5° and 10°, gantry error angle of 2° and 4°. The measurements were analyzed using the inherent gamma passing rate %GP (or gamma failure rate) with 2% and 2 mm criteria and 3% and 3 mm criteria. Results: The results show that the sensitivity of the system depends on the characteristics of irradiated plans. In particular, the stereotaxic plan shows a weakness due to the PTV volume considered and the reduced number of diodes directly interacting whit primary beam. When using 2% and 2 mm criteria and 95% as a pass rate the system detected 11 of 14 errors, while using 3% and 3 mm criteria only 6 of 14 errors were detected (Table 1). Conclusions: Delta4 Phantom+ is an efficient system for QA verification of VMAT, it will be interesting to further analyze the stereotactic case to identify the most suitable procedure.