ESTRO 2020 Abstract Book

S799 ESTRO 2020

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 material filling of sample volume during printing helps to avoid such defects. In this report, the investigation of

Conclusion Compared to a standard CT-based planning approach, MRI- only based planning significantly decreased the dose in all the OARs, in particular in the structures involved in the erectile function. This dosimetric study justifies a clinical trial demonstrating the clinical benefit (toxicity reduction) of this new planning strategy. PO-1485 Comparison of electron beam shaping efficiency with metal and 3D-printed plastic collimators S. Stuchebrov 1 , A. Bulavskaya 1 , Y. Cherepennikov 2 , B. Gavrikov 3 , I. Miloichikova 2,4 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 Electron beam therapy is highly effective for shallow tumors treatment. Modern radiotherapy techniques allow delivering a high single-time dose directly to the target volume. Consequently, there are strict requirements for the spatial profiles of therapeutic beams in order to ensure treatment accuracy. The latter causes a necessity to develop new patient-specific approaches to the shaping of electron beam radiation fields. This report proposes an alternative approach to electron beam shaping with plastic produced by fused deposition modeling instead of standard manufactured by metal cutting or melting. The purpose of this study is to compare the radiation fields of a 6 MeV electron therapeutic beam shaped by the plastic collimator and a standard metal one. Material and Methods In this work, we experimentally obtain the radiation field shapes for the 6 MeV electron beam of the ONCOR Impression Plus medical linear accelerator.