118. Limiti di confidenza per l'assicurazione di qualità pre-trattamento in VMAT con il sistema COMPASS: Site-specific confidence limits in VMAT pre-treatment QA with COMPASS. (December 2018)

• Record Type: Journal Article
• Authors: Sutto, M.; Canonico, D.; Bindoni, L.; Rinaldin, G.; Monti, A.F.; Carbonini, C.; Torresin, A.; Begnozzi, L.
• Is Part Of: Physica medica. Volume 56(2018)Supplement 2
• Page Start: 136
• Page End: 137
• 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.2018.04.129
• Languages: English
• ISSNs: 1120-1797

Abstract

Abstract : Purpose: The aim of this study was to establish site-specific confidence limits (CL) for pre-treatment QA of VMAT plans with COMPASS® (IBA Dosimetry), adopting the AAPM-TG119 approach. Secondly, we reviewed the CL analysing the pre-treatment QA results of clinical plans. Methods and materials: Five AAPM-TG119 benchmark plans (multitarget, C-shape easy, C-shape hard, prostate, head & neck) were optimized with VMAT on a cylindrical homogeneous phantom with Monaco 5.0 TPS (Elekta). Plans were delivered on two Elekta Synergy LINAC equipped with Agility MLC. Plans were independently recalculated by COMPASS before delivery (CC), and then reconstructed from measurements performed with MatriXX Evolution (CR). Dose distributions from TPS, CC and CR were compared using global gamma 3%/3mm and differences in the mean (Dmean ) and near minimum (D99% ) doses of the PTV. CL on gamma passing rate ( γ PR ) and on the differences of the DVH indices were established using the Student's statistics and successively reviewed by analysing the QA results of 41 H&N and 10 prostate plans. Additionally CL on the variability of the DVH indices of the main OAR were established from the analysis of the clinical plans. Results: From the QA of the AAPM-TG119 tests, the CL of γ PR were 99%, 99% and 98%, respectively for CC vs. TPS, CR vs. CC and CR vs. TPS. The CL of Δ D mean / D mean (PTV) were (−1%;+2%), (0%, +1%) and (−1%;+2%) respectively. The CL of Δ D 99 % / D 99 % (PTV) were (−5%;+5%), (−5%, +4%) and (−6%;+4%) respectively. The major dose differences were registered under the Y-jaws, due to non-eliminable differences between predicted and measured dose under the collimators. The analysis of the QA of H&N and prostate plans confirmed or tighten the CL, especially the CL of Δ D 99 % / D 99 % (PTV) were (−5%;+5%), (−5%, +4%) and (−6%;+4%) with the exception of the CL for the γ PR which was broadened to 98% for CC vs. TPS, because the dose values calculated by Monaco and COMPASS disagree in regions with density different from water. Conclusion: Site-specific CL on γ PR and on the percentage difference of mean and near-minimum doses to the target were set for clinical routine QA using AAPM-TG119 tests and tightened or confirmed from the QA analysis of clinical plans.