S927
Clinical - Mixed sites & palliation
ESTRO 2026
SRS is highly effective, rigid fusion of the initial dose may overrepresent the relevant high dose at subsequent SRS. Our aim was to document the volumetric response of BMs following SRS to explore the idea of deformable dose registration. Material/Methods: Retreatment analysis software (Brainlab, Germany) was used to autosegment BM volume, at baseline and following repeat courses of SRS, on T1-weighted MRI scans. The segmented volumes were matched to treated volumes, ensuring consistent tracking. Individual BM volumes from each SRS course were summed to determine the total volume for each treatment group (Group 1: first SRS course PTVs, Group 2: second, etc.). The total volume for each group was tracked across the available MRI scans to quantify the volumetric response. Results: 21 patients with a total of 135 BMs treated in 48 groups were included. A mean of 3 courses (1-5) of SRS with mean of 3 BMs per course (1-12) were delivered. Fractionation was predominantly 1 x 20 Gy to 70% isodose, alternatively 5 x 7 Gy (21 BMs), 5 x 6 Gy (6 BMs), 5 x 5 Gy (5 BMs), and 1 x 18 Gy (3 BMs). Mean time interval between courses was 7.5 months (range 2-34). The cumulative volume irradiated to prescribed dose was greatest for the first course (7.6 cm3) and decreased for subsequent courses (1.36, 0.56, 0.58 cm3). 6/21 (28.5%) patients had a complete response after each course. 1/21 (4.8%) had stable disease. The remaining 14/21 (66%) patients showed partial response (commonly with complete response of groups 2 and 3). 6/21 (28.5%) showed a greater response after C2 and C3 than C1, however, 3/21 (14.3%) had the best response after C1. Across all patients, mean reduction in BM volume was 63% after C1, 91% after C2, and 83% after C3. There was local failure of 1 BM (0.7%) which was re-irradiated. 11 BMs (8.1%) show a temporary increase in volume after C3 and C4, attributed to treatment-related effects.
3039 cc). dHT was administered using the ALBA-4D system (Medlogix®) with a median of 5 sessions (range: 3–8). Pelvic lesion temperatures were monitored with rectal/vaginal probes or bladder catheters, guided by the Plan2Heat system. Temperature profiles, tolerability, patient compliance, toxicity, and clinical outcomes were analysed. Results: The median interval between RT and dHT was 19.5 minutes (range: 16.4–25.2 min). Temperature indices during 66 HT sessions were: T10, 42.19 ± 0.50 °C; T50, 41.25 ± 0.51 °C; and T90, 40.03 ± 0.91 °C. Minimal, average, and maximal mean temperatures were 39.40±1.09°C SD, 41.50±0.70°C SD, and 42.77±0.69°C SD, respectively. Real-time temperature measurements closely matched Plan2Heat estimates. Of the 57 patients, 52 (91%) completed the treatment, with discontinuations due to death (n = 4) or refusal (n = 1). Median RT dose delivered was 38.7 Gy (range: 7– 66 Gy) over 2–33 fractions. Eight patients (15%) declined further dHT due to pain.Acute toxicities were minimal, with ≤ 5% of patients experiencing grade 2 gastrointestinal issues, fatigue, or radiodermatitis. Among the 23 patients treated for pain palliation, 17 (74%) reported symptomatic relief at the end of treatment. Median OS was 3.3 months (range: 0-30.5 months) with 34 patients dead (60%). Of the 21 patients with follow-up imaging, 1 achieved a complete response, 3 had a partial response, 9 had stable disease, and 8 had progressive disease. Conclusion: Concomitant dHT and RT were feasible and well- tolerated across a heterogeneous patient cohort. This combination achieved significant symptomatic pain relief in over 70% of patients and local disease control in 60%, highlighting dHT as a valuable component of multimodal treatment strategies. Keywords: hyperthermia, radiotherapy, outcome Volumetric response following serial stereotactic radiosurgery for multiple metachronous brain metastases. Vesela Beddall, Nicoletta Lomax, Sara Alonso, Christoph Trepte, Roger A Hälg, Oliver Riesterer, Susanne J Rogers Radiation Oncology Center Mittelland, Kantonsspital Aarau, Aarau, Switzerland Purpose/Objective: The challenges of sequential stereotactic radiosurgery (SRS) treatment planning for brain metastases (BMs) include the evaluation of the prior delivered dose. As Digital Poster 4755
Conclusion: There was a clinically relevant reduction in cumulative BM volume (frequently 100%) in 20/21 patients compared to that irradiated at baseline. These data
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