ESTRO 2021 Abstract Book

S1348

ESTRO 2021

VeriSoft software. As an evaluation criterion, 3 mm DTA and 3% DD were used for local dose and gamma passing threshold was set as 90%.

Results It was found that infill percentages, infill patterns and printing directions caused a significant change in the dosimetric property of printed electron compansator as presented in Table 1 and Table 2. Maximum gamma passing rates were found as 97.1% and 98.6% for 6 MeV and 12 MeV electron energies, respectively. According to gamma analysis results, optimal printing parameters for both electron energies were 80% infill-percentage, sunglass fill infill-pattern and horizontal printing direction.

Conclusion Dosimetric properties of the printed electron compensator changed significantly with the selected printing parameters. Therefore, it is important to note that each combination of the printing parameters needs to be investigated separately before using 3D-printed electron compensator in clinical practice. PO-1628 Pre-treatment verification using portal images. Could them substitute our reference phantom? J.D. García Fuentes 1 , P. Retorta 1 , R. Colmenares 1 , D. Sevillano 1 , F. Orozco 1 , A.B. Capuz 1 , M. Cámara 1 , R. Morís 1 , P. Galiano 1 , D. Prieto 1 , M.J. Béjar 1 , F. García-Vicente 1 1 H.U. Ramón y Cajal, Medical Physics, MADRID, Spain Purpose or Objective Our institution has recently acquired Epibeam and Epigray (Dosisoft) software. Both use portal images. The first module converts portal images into dose planes at SAD = 100 cm and z = 5 cm in water which are used to test without a patient, while the second allows volumetric dose reconstruction tracking of each patient session. The main objective of this work is to evaluate the Epibeam (EP), tracing it to ArcCheck (AC), since it is our reference equipment for the VMAT technique. Materials and Methods Ten patients previously treated with 6 MV-VMAT were selected: 5 prostate (3Gy/fr) and 5 head and neck (2.2Gy/fr). Each initial plan (case 0) was subjected to 4 different modifications using a self-developed program (Matlab): the MLC was varied ±1 mm or ±2 mm in one of the banks (cases a and b), as well as with a random error ±1 mm or ±2 mm in each individual leaf at each control point (cases c and d). The roadmap of the work was as follows: i. Dosimetric impact study (DHV in Pinnacle v16.2, Philips) of the modifications. ii. Irradiation on the Linac (Infinity, Elekta) of all the plans both in AC and iviewGT (IW)-EP. iii. Study of different EP gamma index metrics (Global(3%,2mm), G(2,2), G(2,1) and Local(2,2)) to find the one