ESTRO 2020 Abstract book

S101 ESTRO 2020

a generalized horse-shoe shaped oropharhyngeal disease surrounded by two parotids and a spinal cord as avoidance structures. The optimized beams were then copied onto the uncorrected scan, OMAR corrected scan and AMPP corrected scan. The dose distributions were recalculated without reoptimizing the proton beams in order to analyze dose distribution differences. Results Noticeable dose distribution differences were observed in the plans using OMAR corrected and uncorrected scans. Figure 1 shows the same axial slice on the phantom, centered inside the artifact filled region, for all the scan sets. There is under dosing in the posterior region near the spinal cord in the OMAR and uncorrected scans. In contrast, the dose distributions after AMPP show a similar dose distribution to the baseline scan without artifacts. AMPP also showed comparable target coverage compared to the baseline (96.8%) scan with 97.5% of target covered with prescription dose. The plan on the AMPP corrected images also showed a larger number of hotspots inside the target which could be the reason for the higher percentage of target coverage. Alternatively, the uncorrected and the OMAR corrected scans presented lower target coverages, with 84.7% and 77.9%, respectively.

Conclusion CM showed correlation with γ evaluations: as a general behaviour, higher plan complexities were associated with lower concordances between computed and measured doses. Different characteristics of the optimized plans (beam aperture and shapes, leaf travel, variations in speed and acceleration of the MLC, as well as variations of the gantry speed) have a significant influence on the treatment delivery accuracy. Correlations between QA results and CM depend on the technical solution adopted for QA measurements and the detector resolution is a key parameter. PD-0184 Proton dosimetric comparison of CT metal artifact reduction techniques for head and neck patients D. Branco 1 , P. Taylor 1 , S. Kry 1 , X. Zhang 1 , J. Rong 2 , S. Frank 3 , D. Followill 1 1 MD Anderson Cancer Center, Radiation Physics, HOUSTON, USA ; 2 MD Anderson Cancer Center, Imaging Physics, Houston, USA ; 3 MD Anderson Cancer Center, Radiation Oncology, Houston, USA Purpose or Objective Dental metal amalgam filling artifacts obscure the visualization of tissues in the oral cavity and oropharyngeal region leading to poor visualization of the anatomy, potential erroneous patient diagnoses, in addition to negatively impacting the quality of radiation therapy treatments, specifically in proton therapy. The purpose of this study is to compare the proton dosimetric impact of the use of an in-house metal artifact management for proton planning (AMPP) technique and Phillip’s commercial solution (OMAR). Material and Methods A head and neck anthropomorphic phantom composed of proton tissue equivalent materials with a human skull, air cavities and a removable jaw was used. The removable jaw allowed for the exchange of bone equivalent and metal filled teeth inserts for the creation of baseline and artifact filled scans. A clinically relevant proton treatment plan was designed on the baseline scan using two anterior oblique beams and one posterior beam. The target mimics

Conclusion Proton dose distributions were evaluated using different metal artifact reduction techniques. The in-house AMPP algorithm outperformed the uncorrected and OMAR corrected scans showing a treatment plan with a similar

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