S989
Clinical - Oligometastatic cancer
ESTRO 2026
Clinical Trial. JAMA Oncol 2023. DOI:10.1001/jamaoncol.2023.0161 [3] Jooya et al. Patient-reported quality-of-life outcomes after abdominopelvic stereotactic body radiation therapy using an MR-linac system. Int J Radiat Oncol Biol Phys 2025. DOI:10.1016/j.ijrobp.2025.03.052 Keywords: MR-Linac, prostate cancer, SBRT Digital Poster 4542 Feasibility and safety of MR-guided adaptive SABR for re-irradiation of adrenal metastases Miguel A. Palacios, Peter S.N. van Rossum, Anna M.E. Bruynzeel, Bohoudi Omar, Senan Suresh, Famke L. Schneiders Radiation Oncology, Amsterdam UMC, Amsterdam, Netherlands Purpose/Objective: Re-irradiation of adrenal metastases is highly challenging due to cumulative dose constraints of nearby organs-at-risk (OARs). Traditional options are limited. This study describes an innovative, collaborative approach using MR-guided adaptive SABR (MRgSABR) to safely deliver ablative doses in this high-risk patient population [1] . We assessed the feasibility, safety, and dosimetric benefits of this technology-driven, multidisciplinary workflow, aiming to expand non-invasive treatment options [2]. Material/Methods: We identified seven consecutive patients from an ethics-approved database who underwent MR-guided SABR re-irradiation for recurrent or oligoprogressive adrenal metastases between March 2024 and March 2025. All had undergone high-dose radiotherapy with geometric overlap (re-irradiation type 1). Re-irradiation was delivered on an MR-Linac using real-time imaging and daily online adaptive planning. Re-irradiation was delivered using 5 × 10 Gy in five patients (biologically effective dose, BED10=100Gy), 3 × 15 Gy in one patient (BED10=112.5Gy), and one patient completed only three fractions of 10 Gy (BED10=60Gy) due to declining clinical condition. Cumulative doses were estimated by registering initial treatment plans to the re-irradiation imaging. Dosimetric comparisons were made between the original non-adaptive plan and the final adapted plan. Clinical outcomes were assessed. Results: At a median follow-up of 8.6 months, six of seven patients remained progression-free. All treated lesions remained stable per RECIST criteria at last follow-up. Toxicity was acceptable, with no Grade ≥ 3 events reported. One patient experienced a Grade 2 vertebral fracture adjacent to the target; the estimated cumulative EQD2 to 1.0 cc of the vertebra was 101 Gy.
first prostate cancer-directed intervention since treating the primary disease. 8/38 (21.1%) patients commenced ADT with MR-SBRT and were excluded from analysis of biochemical response. Of the remaining 30, 10/30 (33.3%) had rising PSA at first post-treatment assessment; this group included 6 of the 9 patients on study who were castrate resistant. Of 20/30 (53.3%) patients with a PSA response, median time to PSA nadir was 6.5 months (range 1-29), and 8 have not reached biochemical, local, or distant failure at last follow-up (median 25.1 months, range 11.7- 36.6). 20/38 (52.6%) of patients had distant disease progression, detected at a median time of 13.1 months (range 2.8-33.5). 21/38 (55.3%) patients underwent further oncologic intervention during the follow-up period (7 started or intensified ADT, 8 radiotherapy alone, 4 both started ADT and had radiotherapy, 2 chemotherapy), at a median time of 13.1 months (range 3.0-34.9). 91 OMs were treated; of 59 with radiographic follow-up, 2 had evidence of local failure (large iliac bone metastases). One patient, who had MR-SBRT immediately following prostate-directed radiation, had grade 2 genitourinary toxicity. Otherwise, no grade 2 or higher adverse events were recorded. Patient-reported outcomes were available for 30/38 (78.9%) patients. Treatment was well- tolerated for most patients [3] with median patient- reported QoL of 6 out of 7 (range 3-7) after final fraction and at first follow-up.
Conclusion: MR-SBRT was well-tolerated for prostate OM patients with good baseline performance status, across a heterogeneous group by age, OM size, number, previous treatment, castrate status, and disease burden. A minority of patients may reach durable control following MR-SBRT. References: [1] Phillips et al. Outcomes of Observation vs Stereotactic Ablative Radiation for Oligometastatic Prostate Cancer The ORIOLE: Phase 2 Randomized Clinical Trial. JAMA Oncol 2020. DOI:10.1001/jamaoncol.2020.0147 [2] Tang et al. Addition of Metastasis-Directed Therapy to Intermittent Hormone Therapy for Oligometastatic Prostate Cancer: The EXTEND Phase 2 Randomized
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