ESTRO 2020 Abstract Book

S501 ESTRO 2020

Purpose or Objective To evaluate feasibility, treatment compliance and organs at risk sparing in LBCP treated with DIBH (Elekta ABC ® ) in

4 European Institute of Oncology, Department of Medical Physics, Milan, Italy ; 5 European Institute of Oncology, Division of Breast Surgery- European Institute of Oncology- Milan- Italy, Milan, Italy ; 6 European Institute of Oncology, Scientific Directorate- European Institute of Oncology- Milan- Italy, Milan, Italy Purpose or Objective Although the standard treatment of in-breast recurrence (IBR) after breast conservative surgery (BCS) and whole breast radiotherapy (WBRT) is still represented by mastectomy, over the last decade there has been an increasing attitude towards performing a second BCS followed by further radiotherapy (RT) with different techniques (intraoperative RT, brachytherapy, external beam RT). The aim of the study is to evaluate acute toxicity and local control of partial breast re-irradiation (re-PBI) with intensity modulated RT (IMRT), using a hypofractionated scheme. Material and Methods Eligibility criteria included patients previously treated with WBRT who experienced IBR and were operated on with second BCS. Re-irradiation was limited to the tumor bed and was performed using either TomoTherapy® IMRT with helical modality or BrainLab-VERO® IMRT step-and-shoot. Planning target volume (PTV) was generated by clinical target volume (CTV) with a margin of 5 mm. Daily image guided RT was applied by megavoltage fan beam computerized tomography (CT) for TomoTherapy® and kilovoltage cone beam CT for VERO®. For target volume, the PTV planning objectives were V100%≥95%, V95%≥98%, V90%≥100%, Dmax≤110%. Toxicity was evaluated using RTOG/EORTC criteria. Results Between 6/2012 and 3/2018, 59 patients were treated with re-PBI. Prescription dose was 37.05 Gy in 13 fractions. Fifteen (25%) patients were treated with TomoTherapy® and 44 (75%) with VERO®. Overall, median follow-up was 38.7 (1-80) months. Data of chronic toxicity > 1 year are available for 44 (74%) patients; 5%,10%, 5% of patients report fibrosis G3, atrophy G2 and teleangectsia G2, respectively. Ten (17 %) patients showed a subsequent oncologic event 24±12 months after the retreatment: 1 patient had a second IBR distant from the re-PBI field (1.6% cumulative incidence of IBR), 1 patient had regional recurrence, 7 patients developed distant metastasis (lymph nodes, lung, bones and brain) and 1 had other primitive tumors. Conclusion Re-PBI after second BCS represents a feasible alternative to mastectomy with regard to local control, showing good toxicity profile. Longer follow-up is needed to evaluate late toxicity and to establish the role of this treatment modality in local control. Longer follow-up is needed to evaluate late toxicity and to establish the role of this treatment modality in local control. This abstract is the basis for a future article. PO-0938 Deep Inspiration Breath Hold (DIBH) as a standard option in left breast cancer patient (LBCP) A. Huscher 1 , L. Donadoni 1 , A. Taddeo 2 , M. Galelli 3 , T. Prochilo 4 , F. Guerini 5 , S. Mutti 5 , A. Zaniboni 6 , M. Bignardi 1 1 Fondazione Poliambulanza, Radiation Oncology, Brescia, Italy ; 2 University of Brescia, Radiation Oncology Chair, Brescia, Italy ; 3 Fondazione Poliambulanza, Medica Physics, Brescia, Italy ; 4 Fondazione Poliambulanza, Medical Oncology, Brescia, Italy ; 5 Fondazione Poliambulanza, Surgery, Brescia, Italy ; 6 Fondazione Poliambulanza, Oncology Department, Brescia, Italy

daily clinical practice. Material and Methods

459 LBCP treated with ABC ® from 2012 to September 2019 were included in a retrospective analysis. Clinical Target Volumes (CTVs) contouring for breast, chest wall and nodal areas followed ESTRO Guidelines. Whole breast or chest wall CTVs were irradiated, either with 3D conformal technique (3D) or intensity modulated techniques (IMRT). Irradiation of breast/chest wall with nodal areas was always performed with IMRT. Hypofractionation (42.4 Gy in 16 fractions) was prescribed in most cases of whole breast irradiation while 50 Gy in 25 fractions were prescribed in any case of nodal irradiation. Clinically positive internal mammary nodes (IMN) were treated with a Simultaneous Integrated Boost technique (SIB) with doses of 55/50 Gy in 25 fractions. A 9 Gy boost (in 3 fraction) to tumor bed was used when indicated. 3D Treatment planning was performed through Elekta Xio ® and Elekta Monaco ® , while IMRT plans with Elekta Monaco ® . On board imaging included portal imaging for 3D technique and CBCT for IMRT and VMAT. In all cases a standard protocol was applied. Dose metrics for heart and left lung were analyzed, as well as ABC parameters.. Results ABC ® from 2016 represents the standard approach to LBCP irradiation with up to 85% of LBCP treated in the latest years with this technique; in 10% of cases we use prone irradiation or thermoplastic breast mask but about 5% of patients do not show adequate compliance for DIBH. Mean patient age was 56 years (range 28-85 years). Target volumes included in 304 the whole breast, in 28 the chest wall, in 77 the chest wall and supraclavicular nodes, in 43 breast and supraclavicular/axillary nodes and in 7 cases IMN. Hypofractionation was delivered in 252 cases, SIB in 2 cases and the remaining received conventional fractionation. 3D accounted for 53% of treatments while IMRT for 47%. Planned Target Volume mean value was 818 cc (range 2352-162), ABC ® threshold had a mean and median of 1423 and 1500 (range 1000-2000 cc); breath hold time showed mean and median values of 24 and 25 seconds (range 18- 30 s). Lung reference constraints, depending on clinical prescriptions and fractionation, were always respected, and mean left lung dose was 8.2 Gy, (range 4-13.9 Gy). Heart reference constraints, depending on fractionation (V 20Gy for hypofractionation and V 25 Gy for standard fractionation), were always lower than 5% and mean heart dose was 3 Gy, (range 0.9-7, this latter in case of IMN irradiation). All radiation sessions were completed in a 15 minutes slot. Conclusion Routine use of DIBH with ABC ® is feasibile in real time practice and effective in achieving respect of organs at risk. PO-0939 Structured prospective database:exploratory study about toxicity and progression in breast patients. M. Lizondo 1 , J. Fuentes-Raspall 2 , A. Soto 2 , N. Jornet 3 , A. Latorre-Musoll 3 , P. Delgado-Tapia 3 , P. Carrasco 3 , J. Pérez-Alija 3 , P. Gallego 3 , P. Simón 3 , A. Ruiz-Martínez 3 , M. Adrià 3 , I. Valverde-Pascual 3 , M. Barceló 3 , N. Garcia 3 , M. Ribas 3 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 d'Oncologia Radioteràpica, Barcelona, Spain ; 3 Hospital de la Santa Creu i Sant Pau, Servei de Radiofísica i Radioprotecció, Barcelona, Spain