ESTRO 2020 Abstract book

S1057 ESTRO 2020

calculated as the weighted mean of the PCs, as follows:

Resubmitted plans were better optimised as can be seen below. Fig. 1 shows that the average mean nodal (PTVn_4700) doses were closer to 47 Gy in the resubmissions. Fig. 2 shows the average bowel dose was reduced. Similar results were found for the other PTV's and the rectal dose. On-trial plan reviews have been conducted for 27 RT centres. 2 plans failed, 1 was created by a less experienced planner, the other had incorrect outlining of nodal CTV. The plans were modified and patients continued treatment.

where n is the minimum number of PCs corresponding to a cumulative percentage of the total explained variance higher than 80%. v is the sum of the variance explained by the retained PCs and v k the percentage of the variance explained by PC k . A standardized version of this score, sPCS, was then calculated for a given plan i , as:

sPCS is 0 for the audit plan having the minimum PCS (min PCS) and 1 for the audit plan having the maximum PCS (max PCS). The higher the value of sPCS, the superior the plan complexity. Results The first two principal components explained over 90% of the total variance in the original dataset, therefore they were selected to calculate the standardized global plan complexity score. The global score showed that the Eclipse sliding window plans were the most complex and the group formed by Eclipse VMAT plans the one with the highest complexity variability (maximum sPCS of 0.973 and minimum of 0.046, mean±SD = 0.466 ±0.316). The spread in Monaco VMAT plans was much lower (mean±SD=0.104±0.078), being generally less complex than the VMAT Eclipse ones for the evaluated plan parameters. These findings highlight the differences at the national level resulting from different planning strategies and/or planner’s skills. Conclusion The proposed global plan complexity score allowed to have a global overview of the plans complexity, highlighting differences intra and inter groups of technology and IMRT/VMAT technique. Moreover, the proposed methodology can be applied to any given plan set and the resulting standardized plan scores may be taken as unique indicators to compare the global complexity among those plans. PO‐1802 LXA4 attenuates the radiation‐induced pulmonary fibrosis via FPR2. J. KIM 1 , S. Park 1 , S.Y. Han 1 , J. Cho 1 1 Yonsei University College of Medicine, Department of Radiation Oncology, Seoul, Korea Republic of Purpose or Objective Radiation (IR)-induced pneumonitis and pulmonary fibrosis are common side effects of thoracic cancer radiotherapy. Lipoxin A 4 (LXA 4 ) is a lipid mediator as a bioactive product for arachidonic acid and has the anti-inflammatory properties that regulates neutrophil infiltration and proresolving signaling through macrophage polarization and uptake apoptotic neutrophil in a wide variety of tissues and have been reported that LXA 4 exhibit diverse anti-inflammatory action in airways. However, the effects of LXA 4 on IR-induced lung fibrosis have not been investigated before. Also, the problem with current Poster: Radiobiology track: Radiobiology of normal tissues

Conclusion The Trial Launch Workshop engaged planners and enabled faster opening of the first centres. The planning benchmark identified 2 major protocol deviations and was effective in standardising and improving plan quality. Timely retrospective reviews have been sufficient to maintain quality during the trial. PO‐1801 A new standardized global plan complexity score indicator T. Santos 1,2 , T. Ventura 2 , M.D.C. Lopes 2 1 Faculty of Sciences and Technology, Physics Department, Coimbra, Portugal ; 2 Instituto Portugues de Oncologia de Coimbra Francisco Gentil- E.P.E.- Portugal, Medical Physics Department, Coimbra, Portugal Purpose or Objective A new standardized global plan complexity score is proposed with the aim of characterizing and comparing, through a unique indicator, the complexity of the IMRT/VMAT plans created in the context of a national dosimetry audit. Material and Methods Nine metrics, proposed in the literature, assessing different plan complexity features, such as the total monitor units, shape, area, and/or location of the individual beam apertures, have been computed from the DICOM RT files of the 19 IMRT/VMAT head and neck audit plans, using an in-house developed MATLAB program. Principal Component Analysis (PCA) was used to obtain a new reduced set of uncorrelated variables (principal components, PC) that explain most of the variability in the original complexity dataset. To summarize and give a global meaning to the information provided by the new uncorrelated variables, a plan complexity score was