ESTRO 2020 Abstract book

S790 ESTRO 2020

Average overestimation of V5Gy was 9.22 % (std dev 1.5 and P value 0.006). Mean Heart dose obtained by the both algorithms agreed within 3%. Conclusion Lung density decreases for DIBH CT scan. Model based AAA algorithm overestimate low lung dose V5 Gy for DIBH CT scan which is very important parameter for accepting VMAT plan for chest wall. PO‐1397 Validation of two different Monte Carlo engines for secondary independent dose calculation. S. Hofer 1 , P. Ferrari 1 , M. Maffei 2 , M. Haller 1 1 Südtiroler Sanitätsbetrieb, Dienst für medizinische Strahlenphysik, Bozen, Italy ; 2 Südtiroler Sanitätsbetrieb, Dienst für onkologische Strahlentherapie, Bozen, Italy Purpose or Objective Secondary independent dose calculations ( SIDC ) have the potential to identify several problems (heterogeneity calculations, data corruptions, system failures) with the primary TPS, which generally are not identificable with a measurement based approach. The aim of this work is to test two Monte Carlo systems for independent dose calculation in terms of accuracy and to confront them with the Raystation (v 7.0, Raysearch Laboratories) treatment planning system with collapsed cone algorithm. The first Monte Carlo engine (Monaco v 5.11.02 , Elekta Oncology System) is a complete Planning system, which can also be used for SIDC. The second ProSoma Core (v4,1 , MedCom) is only for SIDC and has no accreditation as a TPS. The ProSoma Core Monte Carlo engine has on average, with the same parameters and on similar machines, a ten times shorter calculation time respect to the Monaco TPS. Material and Methods The three dose engines were commissioned for the same Elekta Linac with Agility MLC and a 6MV Photon beam. Twelve Raystation Vmat plans, with two arcs each, for head and neck and pelvic cancer were evaluated. The plans were recalculated on the PTW Octavius 4D QA phantom with a uncertainty of 0.5% and a voxel size of 2mm. Measurements were done with the Octavius 4D phantom and the Octavius 1500 measurement array. Furthermore the plans were calculated with all three dose engines on patients anatomy and evaluated with Gamma Analysis. Results With a global gamma of 2%/2mm the three planning systems showed a mean agreement of 95.1%+-1.5% (Raystation), 96.1%+-1.8% (Prosoma) and 96.4%+-1.5%. (Monaco) with measurement. The Prosoma and Monaco Monte Carlo algorithms showed a significantly better agreement (paired bilateral T test - p < 0.05) with measurement than the Raystation calculations. Between the two Monte Carlo engines the difference was not significant. Regarding the dose to the isocenter the mean deviation between calculation and measurement is the following: - 0.8% +-1.7% (Raystation), -0.7% +-1.3% (Prosoma), -1.5% +- 1.3% (Monaco). The calculation on the patients CT showed no significant difference using a global gamma of 2%/2mm ( mean Gamma value Raystation-Monaco: 97.3%+- 2.4% Raystation-Prosoma: 97.1%+-1.2% and Monaco- Prosoma: 98.2%+-1.9% ). Using a local gamma of 2%/2mm, the agreement between Raystation and Monaco is significantly better than between Raystation and Prosoma.

Conclusion In the homogenous medium of the phantom the Monte Carlo engines showed a significantly better agreement with measurement. The two Monte Carlo systems were equivalent in terms of accuracy. The behavior of the algorithms in the patient anatomy i.e.inhomogenous media has to be subject of further investigations since there were no reference measurements available. The calculations among themselves showed a better agreement between Raystation-Monaco than between Raystation-Prosoma. PO‐1398 Validation and clinical Implementation of Sun Nuclear DoseCHECK and PerFRACTION for Varian Halcyon E. Almond 1 , G. Kidane 1 , A. Ikthaker 1 , Y. Miao 1 1 Queen's Hospital- Barking Havering and Redbridge Hospitals NHS Trust, Radiotherapy, Romford, United Kingdom Purpose or Objective In the UK a Radiotherapy Provider should ensure that an independent dose recalculation is carried out. This recalculation must be independent of the planning computer and independent of the person producing the computer generated plan. When Halcyon TM was first released there was no software based patient specific quality assurance system available in the market to provide an independent pre-treatment verification, due to the beam modelling challenges presented by the Halcyon’s double stacked MLC banks and other Halcyon specific special features. Recently, Sun Nuclear (Melbourne, FL) released DoseCHECK TM , independent 3D dose calculation software for pre-treatment verification, and PerFRACTION TM , a 3D dose reconstruction system using the machine log-file to verify the treatment delivery. The aim of this study was to validate DoseCHECK and PerFRACTION as software based independent patient-specific QA for Halcyon. Material and Methods PDDs were generated in water by the Eclipse v15.6 treatment planning system (Varian, Palo Alto) using the Analytical Anisotropic Algorithm (AAA) and DoseCHECK which uses the Collapsed Cone Convolution Superposition algorithm (CCCS) dose calculation engine. The percentage differences between the PDDs at various depths were compared. 21 patient plans produced by the Eclipse treatment planning system (TPS) which covered a range of treatment sites (Head & Neck, Thorax, Abdomen and Pelvis) were used for this study. The dose distributions produced by the Eclipse TPS were compared to the distributions calculated by DoseCHECK and PerFRACTION. The gamma pass rates (criteria 3%/3mm, global