ESTRO 2020 Abstract book

S844 ESTRO 2020

Results D98 was larger than 95% prescription dose for all patients. Fig.2 shows OAR DVHs parameters time evolution between RT techniques. Heart D mean decreased over time due to the increased concern about cardiotoxicity and the consequent change in dose constrains (from 10 to 6Gy for left breast and 3 for right breast). The impact of the IMRT planning learning curve can be seen in the first year. IMRT increased D mean to heart and to CtlBreast compared with 3DCRT. VMAT significantly increased doses received by liver and CtlBreast (p<0.05). DBHI decreased doses to heart significantly with respect to non DBHI(p<2.2e-16).There was no correlation between DVHs parameters and the physician in charge. No correlation between PTV volumes and DVHs parameters was found.

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.

Conclusion The first patients treated with IMRT showed high doses in OAR. This shows the importance of training and external peer review when a new technique is used. Systematic collection of DVH parameters on a database allows to monitor doses to OAR helping to identify any special causes that could represent relevant changes both regarding equipment, change of practice o new personnel. For instance, VMAT significantly increases doses to OARs away from PTV, and should be used with care on breast cancer patients. As European guidelines had been always followed, the analysis made can provide useful information to other institutions that are going through technological changes. Acknowledges: This work was financed by the Spanish Association Against Cancer (AECC) PO-1480 Position in breast cancer radiotherapy: dosimetry and toxicity D. Hernandez 1 , M.S. Talaya 2 , C. Anson 1 , P. Castro 1 , M. Roch 1 , P. García 1 , S. Martín 2 , A. Valiente 2 , A. Viñals 1 , R. Capilla_Fayos 1 , M.T. Murillo 2 1 H.U.La Princesa, Medical Physics, Madrid, Spain ; 2 H.U.La Princesa, Radiation Oncology, Madrid, Spain

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