ESTRO 2025 - Abstract Book

S1791

Clinical – Upper GI

ESTRO 2025

2116

Digital Poster Stereotactic Body Radiotherapy (SBRT) for treatment of multiple liver metastases: dosimetric and clinical analysis Ilaria Morelli 1 , Mauro Loi 1 , Michele Aquilano 2 , Marianna Valzano 1 , Giulio Frosini 1 , Pierluigi Bonomo 1 , Alessandra Galardi 1 , Gabriele Simontacchi 1 , Emanuela Olmetto 1 , Viola Salvestrini 1 , Marco Banini 1 , Andrea Romei 1 , Beatrice Bettazzi 1 , Ilaria Bonaparte 1 , Luca Burchini 1 , Cecilia Petruccioli 1 , Luisa Caprara 1 , Doruntina Cela 1 , Livia Marrazzo 3 , Margherita Zani 3 , Lorenzo Livi 1 1 Radiation Oncology, Azienda Ospedaliero-Universitaria Careggi, Florence, Italy. 2 Cyberknife Centre, Istituto Fiorentino di Cura e Assistenza (IFCA), Florence, Italy. 3 Medical Physics Unit, Azienda Ospedaliero-Universitaria Careggi, Florence, Italy Purpose/Objective: Evidence regarding the use of SBRT for the treatment of 4 or more liver metastases (LM) is limited. We present preliminary clinical and dosimetric data from patients treated with SBRT for ≥4 LM. Material/Methods: We retrospectively collected data from patients with miscellaneous metastatic primary tumors treated at our Institution for multiple (≥4) LM from July 2023 to October 2024. Abdominal compression (AC) was applied to all patients. An isotoxic approach was applied where a dose prescription to the PTV between 55 and 35 Gy in 5 fraction was chosen in relation to the following constraints to dose-limiting adjacent organ at risk (OAR): mean liver dose (MLD) should be inferior to 15.2 Gy while at least 700 cc of healthy liver (i.e. liver minus all GTVs) should mandatorily receive less than 21 Gy; duodenum, bowel and stomach should not receive more than 35 Gy to 0.5 cc (D 0.5 ). Prescription dose, number of LM, GTV volumes, healthy liver volume and dose to OARs were determined. To assess target coverage, volume receiving 95% of the prescription dose (V95%) was defined for each PTV, aiming at a 95% dose threshold. Results: Data from 9 patients, 11 treatment plans and 63 metastases were reported. Primary tumor type was melanoma (n=3), breast (n=2), colo-rectal (n=2), kidney (n=1) and pancreatic (n=1) cancer. Median number of LM was 6 (4-8). Median GTV volume was 4.5 (range 0.5-56.7) cc. Two patients received a second SBRT course for out-of-field recurrent LM. Median dose prescription was 45 Gy (35-55) in 5 fractions. Median healthy liver volume was 1179.46 cc (1005.1 1523.8). Median MLD was 17.92 (11.6-25.7): a MLD<15.2 Gy was obtained in 3/11 plans. In all cases, at least 700 cc of healthy liver received less than 21 Gy (range 702-1007). A D 0.5 <35 Gy was achieved in duodenum (median 19.96 Gy, range 6.15-34.65), bowel (median 26.20 Gy, range 8.06-34.80) and stomach (median 23.83 Gy, range 15.23-34.14). For PTV, median V95% was 97.4% (range 90-99%): V95%>95% was achieved in 59/63 cases. At a median follow-up of 13 (range 2-15) months, no grade ≥3 toxicity was observed. Conclusion: Simultaneous SBRT with AC for ≥4 LM is feasible and was not correlated with severe toxicity. Using an isotoxic dose prescription strategy, mandatory dose constraints to OARs were met, with the exception of MLD <15.2 Gy. Adequate PTV coverage was obtained in the majority of cases.

Keywords: SBRT, liver, oligometastases