ESTRO 2020 Abstract Book

S794 ESTRO 2020

PO-1479 OARs dose volume parameters temporal evolution in Breast Cancer RT treatment in a single institution M. Lizondo 1 , N. Jornet 2 , A. Latorre-Musoll 2 , P. Delgado- Tapia 2 , P. Carrasco 2 , J. Pérez-Alija 2 , P. Gallego 2 , P. Simón 2 , A. Ruiz-Martínez 2 , M. Adrià 2 , I. Valverde-Pascual 2 , M. Barceló 2 , N. Garcia 2 , M. Ribas 2 1 Institut de Recerca Hospital de la Santa Creu i Sant Pau, Servei de Radiofísica i Radioprotecció, Barcelona, Spain ; 2 Hospital de la Santa Creu i Sant Pau, Servei de Radiofísica i Radioprotecció, Barcelona, Spain Purpose or Objective During the last decade our department has changed breast treatment techniques and also has merged with another department. The impact of human and technology factors on DVH for PTVs and OARs are reported and analysed. Material and Methods We analysed the DVHs of 1351 breast cancer patients treated with radiotherapy from 2013 to 2019 in one single institution, which incorporated all the personnel from other radiotherapy department in 2017. 3DCRT being still the standard technique, and IMRT(2013), VMAT(2018) and DBHI(2015) implemented in patients not fulfilling dose objectives and constraints. OARs and PTVs contouring followed the ESTRO breast cancer group guidelines. Patients were treated on a Clinac2100CD with RPM respiratory motion system(Varian). Fig.1 shows patient’s treatment characteristics. DVHs parameters were automatically recorded on an external database(RedCap). DVHs parameters extracted were for PTV D98, for heart structure D mean , D2 and V25, for lungs V5, for ipsilateral lung (IpsLung) V20, for contralateral breast (CtlBreast) V5, and for liver the D mean . Dose values were normalized to dose prescription of 50Gy to avoid differences due to different dose fractionations. PTV breast and boost volumes were extracted from Eclipse by scripting. DVHs parameters time evolution was studied. Statistical differences between those parameters by year or physician were determined by Krustal-Wallis test, and correlations between DVHs parameters and PTV volumes (breast and boost) were determined by Spearman’s rho statistic.

obtained with breath hold techniques in 3D-CRT technique. VMAT and IMRT should be reserved only for especially challenging cases of WBI. PO-1478 The effect of magnetic port density on dose distribution in 3D, IMRT, VMAT for breast radiotherapy A. Rygielska 1 , A. Walewska 1 , M. Gabor 1 , D. Pruska-Pich 1 , B. Czeremszynska 2 , L. Kepka 2 1 Military Institute od Medicine, Radiotherapy Department- Laboratory of Medical Physics, Warsaw, Poland ; 2 Military Institute od Medicine, Radiotherapy Department, Warsaw, Poland Purpose or Objective Postmastectomy radiotherapy following immediate breast reconstruction is increasingly used in the treatment of patients with breast cancer. It means that patients are irradiated with a tissue expander (TE) in place before permanent implant exchange. The purpose of this study is to evaluate the influence of magnetic port (MP) in expander on dose distribution for 3D, IMRT and VMAT techniques in case of lack of full technical specification of the magnetic port. The effect of relative electron density (rED) values given to different parts of port was examined too. Material and Methods The CIRS phantom (CIRS Inc. USA) and expander (Nagor Ltd. the United Kingdom) were used. Three single MOSFET detectors (Best medical, Canada) were placed on expander surface under the 2 mm orfit (used for attach expander to phantom). Mosfets were positioned on the top (named A), proximal (B) and distal (C) part of “breast” (Fig. 1). 1 cm silicon bolus (Klarity Medical, USA) was placed on the top. PTV was delineated as usual in such a treatment situation. The total dose was prescribed to PTV mean dose as 39.9 Gy in 15 fractions. Three types of plan: 3D-CRT, IMRT and VMAT (all 6X) was prepared using Monaco v.5.1 (Elekta) treatment planning system (TPS). As we hadn’t a full technical specification of magnetic port (material and dimensions) we made contour for port and divided it into two parts with different density. For planning, we used two types of CT: with the overwritten rED (equals the average number of rED in each volume of MP) and with ‘row’ rED (without overwritten rED). Every plan was irradiated three times, and doses from every mosfet were collected.

Results We obtained agreement with TPS within 4.8% using for planning CT with overwritten rED for magnetic port for all of the tested techniques. In case of using ‘row’ CT (including artefacts, without overwritten density) the difference is higher (up to 6.8 %). In both situations, the biggest difference was noticed for IMRT plan (point A, the nearest to MP). Conclusion In case of lack of the full technical specification of expander (especially magnetic port) the CT with the average number of rED in each part of magnetic port may be used in routine.