ESTRO 2021 Abstract Book

S914

ESTRO 2021

For the purpose of this study, simulation CT-scans of five female patients who underwent RT for lung cancer with CyberKnife at European Institute of Oncology were selected. Using the 4 dimension-computed tomography (4D-CT) images, benign lumps in the breast were identified and served as surrogate of target volume. They were contoured on both the maximum inspiration and the maximum exhalation phases of 4D-CT and an Internal Target Volume (ITV) was obtained. Three treatment plans per patient were optimized prescribing 18 Gy, 21 Gy and 24 Gy at 85% isodose to the ITV. The treatment plans were evaluated taking into consideration the recommendation by Timmerman. Results Fifteen treatment plans were compared. Fourteen treatment plans had an average target coverage of 98.5% (91% - 99.9 %) and fulfilled all the OARs constraints. In only one case, where the lump was close to the skin and the prescribed dose was 24 Gy (85% isodose), target coverage was 84.1% in order to satisfy the D max skin constraint of 27.5 Gy. Conclusion This preliminary investigation highlighted a possible issue in satisfying the constraints by Timmerman when the higher dose level of the dose-escalation study (24 Gy) is used and the breast lump is close to the skin. Subcutaneous lesion localization has been already recognized as challenging and, if the 24 Gy threshold is safely reached in the dose-escalation, it may have clinical implications for patients’ selection and treatment. PO-1098 Standard Radiotherapy Fractionation Toxicity Versus Ultra-Hypofractionation In Breast Cancer. C. Escuin 1 , M. Cerrolaza 1 , V. Navarro 1 , A. Lanuza 1 , A. Campos 1 , S. Flamarique 1 , C. García 1 , M. Gascón 2 , P. Sanagustin 1 , A. Pardo 2 , R. Ibañez 1 1 university Hospital Miguel Servet, Radiation oncology, Zaragoza, Spain; 2 University Hospital Lozano Blesa, Radiation oncology, Zaragoza, Spain Purpose or Objective Radiotherapy is an essential treatment in the local control of breast cancer. Standard treatment is currently carried out in 15 daily sessions. At present, following the results of the phase III Fast-Foward trial and in view of the situation triggered by COVID-19, the number of sessions has been reduced to 5. The RHEMA (extreme hypofractionated radiotherapy in breast cancer) study has been initiated in Spain. It is a multi-hospital study designed to determine the evolution of the change in fractionation. The hypothesis is that the change in fractionation does not increase acute toxicity. The aim of the study was to determine whether there are differences in acute skin toxicity in breast cancer patients who receive adjuvant radiotherapy according to the different fractionation schedules applied. Materials and Methods We retrospectively analysed skin toxicity in patients treated with glandular radiotherapy at the end of treatment and one month later. Out of 75 patients treated with the ultra-hypofractionated schedule, 58 patients with a follow-up of more than 1 month were compared with 38 patients who received the standard schedule, all of whom were treated in 2020 in the Multihospital Clinical Unit of Radiation Oncology of Aragon. In the case of the ultra-hypofractionated treatment, as indicated in the GEORM (Spanish group of breast radiation oncology) guidelines at the beginning of the pandemic, was carried out in 5 sessions with a total dose of 26 Gy over the breast and 29 Gy over the tumour bed, while the standard treatment, consisted in 15 sessions with a total dose of 40.5 Gy over the breast and 48 Gy over the tumour bed. Results The median age was 61 years in the standard group and 63.4 years in the ultra-hypofractionated group. No significant differences were observed in the histological profile. Differences were found in toxicity at the end of treatment, being significantly higher in the standard group (p 0.03). On the other hand, no differences were found in toxicity one month after the end of treatment. Grade 2 toxicity appeared in 2 patients from the ultra-hypofractionated group and 4 from the standard group, with no significant difference (p 0.943). There were no differences in the development of grade 1 toxicity and no grade 3 or higher toxicity was observed. Conclusion It can be concluded that the use of the ultra-hypofractionation schedule compared to standard treatment was not associated with an increase in acute skin toxicity in our series. This is a change in fractionation that could be adopted as a routine treatment in radiation oncology departments after verifying the results with a larger number of patients and a longer follow-up. PO-1099 To plan and deliver adjuvant breast radiotherapy over 1 week: 1-week breast workflow implementation G. Louvel 1 , C. Milewski 1 , G. Auzac 2 , F. Villaret 1 , M. Ung 1 , K. Berthelot 1 , E. Folino 2 , P. Ezra 1 , E. Roberti 2 , I. Yessoufou 1 , M. Cheve 1 , N. Fournier-Bidoz 2 , N. Paragios 3 , E. Deutsch 4 , S. Rivera 1 1 Gustave Roussy, Radiation Oncology, Villejuif, France; 2 Gustave Roussy, Radiation oncology, Villejuif, France; 3 CentraleSupélec-Therapanacea, Centre of Artificial Intelligence in Radiation Therapy and Oncology, Saclay, France; 4 Gustave Roussy , Radiation Oncology, Villejuif, France Purpose or Objective To limit hospital visits and transportation of the patients with early breast cancer (BC) especially during the covid-19 pandemic, we aimed to implement a workflow of treatment to prepare and deliver adjuvant breast radiotherapy (RT) within 1 week. Materials and Methods Based on the Fast Forward RT schedule of 5 fractions of 5.2 Gy over 5 days for adjuvant BC, we designed a workflow to perform BC RT over 1 week from the first RT consultation to the end of treatment (figure 1).