S262
Clinical - Breast
ESTRO 2026
Results:
Digital Poster 1879 Dosimetric analysis for single fraction radiation therapy in breast cancer: CRYSTAL trial Marco Lucarelli 1 , Maria Alessia Zerella 1 , Samantha Dicuonzo 1 , Damaris Patricia Rojas 1 , Anna Morra 1 , Maria Alessandra Gerardi 1 , Cristiana Fodor 1 , Elena Rondi 2 , Silvia Penco 3 , Manuela Sargenti 4 , Paola Baratella 4 , Elena Vicini 4 , Consuelo Morigi 4 , Sabrina Kahler-Ribeiro-Fontana 4 , Viviana Enrica Galimberti 4 , Sara Gandini 5 , Giulia Cursano 6 , Elisa De Camilli 6 , Giuseppe Renne 6 , Federica Cattani 2 , Paolo Veronesi 7,8 , Roberto Orecchia 9 , Barbara Alicja Jereczek-Fossa 1,8 , Maria Cristina Leonardi 1 1 Department of Radiation Oncology, European Institute of Oncology IRCCS, Milan, Italy. 2 Unit of Medical Physics, European Institute of Oncology IRCCS, Milan, Italy. 3 . Division of Breast Radiology, European Institute of Oncology IRCCS, Milan, Italy. 4 . Division of Breast Surgery, European Institute of Oncology IRCCS, Milan, Italy. 5 . Department of Experimental Oncology, European Institute of Oncology IRCCS, Milan, Italy. 6 Division of Pathology, European Institute of Oncology IRCCS, Milan, Italy. 7 Division of Breast Surgery, European Institute of Oncology IRCCS, Milan, Italy. 8 Department of Oncology and Hemato-oncology, University of Milan, Milan, Italy. 9 Scientific Directorate, European Institute of Oncology IRCCS, Milan, Italy Purpose/Objective: This investigation evaluates the dosimetric quality of radiotherapy (RT) plans developed for the CRYSTAL trial (NCT04679454), a monocentric, single-arm, open- label phase I/II study, supported by Fondazione AIRC and designed to assess the impact of pre-operative ablative RT on early stage breast cancer (BC). The objectives were: first, the dosimetric coverage of the target volume, and second, the adherence to dose constraints for organs at risk (OARs). Material/Methods: The treatment planning process utilized preoperative MRI, with fiducial markers in place. This MRI dataset were subsequently used for registration with RT computed tomography images. For target delineation, the GTV was expanded by a uniform 0.5 cm margin to create the CTV, which, for this protocol, was defined as coincident with the PTV. All RT plans were generated on the Cyberknife Treatment Planning System (Precision, Accuray), using a non-coplanar and non- isocentric approach. Dosimetric objectives and OAR constraints were established based on criteria from the National Surgical Adjuvant Breast and Bowel Project B-39/Radiation Therapy Oncology Group 0413 partial breast trial1.
A total of 18 RT plans were included, comprehending 9 right-sided and 9 left-sided BC. The mean PTV volume was: 17.2 ml (±16.1 ml). For all patients, the total dose was prescribed to the 85% isodose line. The median prescription dose for the cohort was 22.5Gy. In phase I, the trial contemplated a dose escalation with 3 patients receiving 18Gy, 3 patients receiving 21Gy and 4 patients receiving 24Gy. In phase II, started in 2023 and still on going, all patients received 24Gy. The mean PTV coverage of 96.49% (±3.34%). Dosimetric analyses for OARs were found to be well within protocol constraints, as shown in Table I: the mean DMAX to the spinal cord was 0.6Gy (±0.36 Gy), below the 14Gy limit, and the mean DMAX to the heart was 2.3 Gy (±2.1 Gy), well under the 22Gy constraint. Excellent sparing was also observed for the ribs (median DMAX 14.6Gy ±8.4Gy; constraint DMAX<33 Gy) and the skin (DMAX 19Gy ±6.3Gy; constraint DMAX<27.5 Gy). Both lungs exposure was minimal, with a median V7.6Gy of 3.4ml (±6.8ml), significantly below the 1000ml constraint. The contralateral breast was the most challenging OAR, with a median DMAX of 0.68Gy (±0.33Gy), which closely approached the protocol constraint of <0.7Gy. Conclusion: This dosimetric study confirmed that the CRYSTAL- specified treatment planning methodology successfully achieved excellent target volume coverage, affirming the technical safety and feasibility of this single-fraction, ablative, pre-operative RT for early BC. References: 1. NSABP B-39, RTOG 0413: A Randomized Phase III Study of conventional whole breast irradiation versus partial breast irradiation for women with stage 0, I, or II breast cancer. Clin Adv Hematol Oncol. 2006 Oct;4(10):719-21. PMID: 17111558. Keywords: Dosimetric, CyberKnife, Pre-operative
Digital Poster 1959
Management of spinal disease in metastatic breast cancer in a UK tertiary hospital: a single centre experience Annie Zhao 1 , Audrey Le Bihan 1 , Saman Jalilzadeh Afshari 1 , Victoria Bradley 2 , Emma M Kenney-Herbert 3
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