S929
Clinical - Mixed sites & palliation
ESTRO 2026
T2, MDA evaluation was available for 40 lesions: 20(50%) CR, 7(18%) PR, 9(22%) SD and 4(10%) PD. In five lesions, cortical interruption was consistent with post-SBRT bone remodeling rather than disease.For RECIST, T2 data (n=19) showed 10(53%) CR, 1(5%) PR, 7(37%) SD and 1(5%) PD . Among lesions assessable with both criteria, discordance between MDA and RECIST was shown in 3/19 lesions (k=0.105). Conclusion: MDA criteria enable evaluation of RM after SBRT, including those lacking measurable soft-tissue components excluded by RECIST. Slight concordance was observed between MDA and RECIST in evaluable lesions. Given the thin cortical bone of the ribs and their susceptibility to radiation-induced remodeling, response assessment requires caution. Site specific response criteria need to be developed based on larger cohorts and longer follow-up. References: doi:10.1007/s00330-024-11006- wdoi:10.7150/jca.1.80doi:10.1016/S1470- 2045(15)00166- 7doi:10.1016/j.ijrobp.2015.07.2288doi:10.1016/j.jos.20 18.08.018doi:10.3390/ijms17091391 Keywords: rib, sbrt, radiological assessment Poster Discussion 4799 Phase III randomized trial comparing Preoperative versus Postoperative Hypofractionated radiosurgery for large brain metastases. Support Trial Pierina Navarria 1 , Federico Pessina 2,3 , Elena Clerici 1 , Antonio Marco Marzo 1 , Giuseppe Minniti 4 , Silvia Chiesa 5 , Paola Anselmo 6 , Fabio Trippa 6 , Michela Buglione Di Monale E Bastia 7 , Francesca Giordano 8 , Cesare Guida 8 , Riva Marco 3 , Anna Maria Ascolese 9 , Laura Fariselli 10 , Isacco Desideri 11 , Lorenzo Livi 11 , Valentini Pinzi 10 , Ciro Franzese 1,3 , Marta Scorsetti 1,3 1 Radiotherapy and Radiosurgery, IRCCS Humanitas Research Hospital, Rozzano, Italy. 2 Neurosurgery, IRCCS Humanitas Research Hospital, Rozzano, Italy. 3 Biomedical Sciences, Humanitas University, Pieve Emanuele, Italy. 4 Radiological Science, Oncology nd Anatomical Patology, Sapienza University, Rome, Italy. 5 Radiotherapy, Policlinico Gemelli, Rome, Italy. 6 Radiotherapy, S.Maria Hospital, Terni, Italy. 7 Department of Radiation Oncology, ASST Spedali Civili and Brescia University, Brescia, Italy. 8 Radiation Oncology, Ospedale del Mare, Napoli, Italy. 9 Radiotherapy, St. Andrea Hospital, Rome, Italy. 10 Radiotherapy, Neurological Institute Carlo Best, Milan, Italy. 11 Biomedical, Experimental and Clinical
evaluation. Keywords: Leptomeningeal spread, surgery, postop- SRS
Digital Poster 4783 Applicability of MDA versus RECIST criteria in the evaluation of response to stereotactic body radiation therapy in rib metastase Chiara Mattioli, Silvia Ruggeri, Mauro Loi, Gabriele Simontacchi, Vanessa Di Cataldo, Giulio Francolini, Emanuela Olmetto, Vieri Scotti, Mangoni Monica, Alessandra Galardi, Andrea Rampini, Beatrice Bettazzi, Matteo Mariotti, Giulio Frosini, Giulia Cesari, Cecilia Petruccioli, Luisa Caprara, Doruntina Cela, Lorenzo Livi Radiation Oncology Department - Careggi Hospital, University of Florence, Florence, Italy Purpose/Objective: Assessment of bone metastases response to stereotactic body radiation therapy (SBRT) using RECIST 1.1 is limited to lesions with measurable soft- tissue components. In contrast, the MD Anderson (MDA) criteria account for radiologic bone features such as sclerosis, offering broader evaluability. This study compared MDA and RECIST in assessing the response of rib metastases (RM) treated with SBRT. Material/Methods: RMs treated with SBRT between 2015 and 2024 were retrospectively reviewed. Inclusion required baseline (T0) and 6-month post-treatment (T1) CT scans: when available, a later CT (T2) was analyzed. SBRT was delivered via VMAT or robotic systems with dose- intensive regimens (16–35 Gy in 1–5 fractions; median 24 Gy, EQD2 47 Gy ₁₀ ). Lesions were classified as lytic, sclerotic, or mixed. MDA criteria were applied to all lesions, while RECIST 1.1 was used only for measurable extra-osseous components ( ≥ 10 mm). Responses were categorized as complete (CR), partial (PR), stable disease (SD), or progressive disease (PD). Concordance in terms of CR rate between the 2 modalities was assessed using the k-index. Results: Fifty RMs in 44 patients were analyzed: 48%(24) lytic, 28%(14) sclerotic, 24%(12) mixed. Primary tumors were mainly prostate (n=16, 36%) and NSCLC (n=11, 22%). At T1, MDA(n=50/50) responses were CR 38%(n=19), PR 24%(n=12), SD 32%(n=16), and PD 6%(n=3), yielding an overall response rate (ORR) of 62%. RECIST(n=22/50) assessement showed CR 45% (n=10), PR 14% (n=3), and SD 41% (n=9), for an ORR of 59%. Among lesions assessable with both criteria, slight agreement was found between MDA and RECIST (k=0.136) due to discordance between 5/22 lesions.At
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