ESTRO 2020 Abstract book

S849 ESTRO 2020

material filling of sample volume during printing helps to avoid such defects. In this report, the investigation of electron beam percentage depth dose (PDD) in 3D-printed samples with different material filling is performed. Material and Methods To optimize the manufacturing of plastic shaping samples, numerical simulation of electron beam PDD in 3D-printed samples is carried out in 100-75% material filling (k) range with the 5% step. For these purposes, the cubic PLA samples (50% C, 5.6% H, 44.4% O) are created with UP! Plus 2 by fused deposition modelling. The measured densities are varied from 1.2 g/cm 3 (k=100%) to 0.9 g/cm 3 (k=75%). Geant4 toolkit is used for clinical electron beam model creation. The radiation parameters are selected according to real 6 MeV extracted electron beam of ONCOR Impression Plus medical linear accelerator. The statistical error for the calculated results is less than 1%. Results The electron beam PDD in 3D-printed samples with 100- 75% material filling is simulated using a created model. It is shown that the depth of the dose maximum (R Dmax ) is shifted with material filling factor changing. R Dmax values equals to 12 mm (k=100%), 14 mm (k=90%), 16 mm (k=80%) and 17 mm (k=75%). The half-value depth (R 50 ) equals to 18 mm (k=100%), 21 mm (k=90%), 23 mm (k=80%) and 24 mm (k=75%) accordingly. The plastic sample thickness required for electron beam total absorption (R max ) are 25 mm (k=100%), 28 mm (k=90%), 30 mm (k=80%) and 32 mm (k=75%). Conclusion The obtained results allow us to conclude that electron beam shaping devices can be produced using fused deposition modelling with variable material filling of sample volume. It is shown that for k=90% the main parameters of electron beam PDD (R Dmax , R 50 , R max ) are shifted to 3 mm and for k = 80% to 5 mm. This does not significantly increase the samples printing time to achieve a given sample thickness. At the same time, the manufacturing quality of such samples significantly higher in comparison with 100% filling. This work is supported by the Russian Science Foundation, project No. 19-79-10014. References 1. Miloichikova I. et al. (2019). Physica Medica , 64, 188- 194. 2. Miloichikova I. et al. (2019). Radiotherapy and Oncology , 133, S1008-S1009. PO-1487 Proton versus photon therapy in locally advanced cervical cancer; a dosimetric study D. Abdulwahid 1 , D. Lines 2 , P. Stich 2 , J. Lee 2 , L. Barraclough 1 , P. Hoskin 1 1 The Christie NHS trust, clinical oncology, Manchester, United Kingdom ; 2 The Christie NHS trust, Physics, Manchester, United Kingdom Purpose or Objective To investigate whether protons deliver comparable target dose whilst reducing organs at risk (OAR) doses for the external beam component of cervical cancer treatment which could allow dose escalation for the brachytherapy component and improve toxicities. Material and Methods Five patients who received radical chemoradiation with a Volumetric Modulated Arc Therapy (VMAT) technique using the EMBRACE II protocol for definition of planning volumes and constraints. The prescribed dose to the planning- target volume primary (cervix, uterus, pelvic ± para-aortic lymph nodes) was 45 Gy in 25 fractions. The SIB dose for the involved nodes was 55 Gy in four patients. They were retrospectively replanned with single field (SFO) and multi-field (MFO) optimised proton plans. The lower target constraints were 95% of the prescribed dose in 95% of the target volume. For every patient, target parameters as well as V20, V30,V40 to the organs at risk (bladder and

In this work, we experimentally obtain the radiation field shapes for the 6 MeV electron beam of the ONCOR Impression Plus medical linear accelerator. The metal collimator shapes are calculated using the XiO dosimetry planning system. The collimator with these shapes is casted using special CIVCO furnace and A-158 alloy (50 % bismuth, 26.7 % lead, 13.3 % tin, 10 % cadmium). To print a plastic collimator, its 3D model is designed based on the same field shapes from the XiO dosimetry planning system. The collimator is made of PLA-plastic by rapid prototyping using the Prusa Mk2 printer. The thickness of the plastic collimator is chosen accordingly to the data of electron beam total absorption obtained in previous researches [1, 2]. To obtain the radiation field of the shaped electron beam pre-calibrated Gafchromic EBT3, dosimetry film is used. The film is fixed perpendicularly to the beam propagation on the surface of the solid tissue equivalent phantom SP34. The source-to-surface distance equals to 100 cm, collimator to the surface distance equals to 6.3 cm. Results The resulting images obtained by the dosimetry films radiation fields is analyzed using an ad-hoc MATLAB program code. The electron beam shapes obtained with metal and plastic collimator are compared by overlapping of the images. The quantitative matching of the electron beam radiation fields dose distribution for both collimators is shown (maximum dose difference is 3 %) as well as quality matching of the field shapes and collimator holes. Conclusion Observed results demonstrate that usage of the samples manufactured using PLA-plastic and fused deposition modeling makes it possible to effectively collimate electron beams and refuse metal collimators which are difficult to use. This work is supported by the Russian Science Foundation, project No. 18-79-10052. References 1. Miloichikova I. et al. (2019). Radiotherapy and Oncology , 133, S1008-S1009. 2. Miloichikova I. et al. (2019). Physica Medica , 64, 188- 194. PO-1486 Electron beam depth dose distributions in 3D-printed samples with different material filling factor S. StuchebroV 1 , A. Bulavskaya 1 , Y. Cherepennikov 2 , B. Gavrikov 3 , I. Miloichikova 2,4 , N. Turgunova 4 1 Tomsk Polytechnic University, Research School of High- Energy Physics, Tomsk, Russian Federation ; 2 Tomsk Polytechnic University, School of Nuclear Science & Engineering, Tomsk, Russian Federation ; 3 Moscow City Oncological Hospital No. 62, the 1st Radiological Department, Moscow, Russian Federation ; 4 Cancer Research Institute of Tomsk National Research Medical Center of the Russian Academy of Sciences, Radiotherapy Department, Tomsk, Russian Federation Purpose or Objective The main aim of radiation therapy is to treat malignant tumors by ionizing radiation with minimum damage to normal tissues located near the irradiation area. Individual shaping samples are created for electron beam radiotherapy to reach this aim. These allow to individualize configuration for the irradiation of neoplasms located close to critical organs. One of the promising ideas is applying an additive technology to the manufacturing of such samples [1, 2]. Application of 3D-printing can increase the effectiveness of electron-beam based treatment methods by reducing time and increasing manufacturing accuracy. The feature of the samples production by fused deposition modelling with 100% filling of the volume with printing material, is a high probability of product defects. Reducing