S1002
Clinical – Paediatric tumours
ESTRO 2026
Digital Poster Highlight 1014
2012 to April 2025. Primary endpoints were relapse rate and overall survival. Relapse was defined as in- field (relapsed within the ≥ 95% isodose region), marginal (relapsed within the 19.9-94.9% isodose region) and out-field (relapsed within the 0-20% isodose region). Results: 45 patients were treated, delivered using conformal radiotherapy (CRT) (n = 23) or VMAT (n = 22). Median age was 5 years (range: 1-49). Right sided tumours were more common (60%), pathological stage III (82.2%), and intermediate risk histology (66.7%). Patients with high-risk histology (31.1%) comprised 6/23 patients in CRT group and 8/22 patients in VMAT group. Irradiated sites included flank only (n = 27), flank + lung (n =17), and flank + lung + liver (n = 1). Median follow-up from diagnosis was 6.4 years (range:0.75-13.4), with 4-year progression free survival of 76% for both CRT and VMAT groups.The median prescribed flank radiotherapy dose was 14.4Gy in 8 fractions (range:12-25.2 Gy; 1.5-1.8Gy per fraction). The overall relapse rate was 20% (n = 9), occurring at median of 1.3 years from diagnosis. In-field relapse was observed in 2 CRT patients and 1 VMAT patient. For the flank-only irradiation group (n = 27); out-field relapses occurred in 3 patients in CRT group and 1 patient in VMAT group. The out-field relapse sites were lung (n = 3), and testes (n = 1). Overall mortality was low at 4.4% (n = 2), both with high-risk disease, with median time from diagnosis to death 2.3 years. Conclusion: The adoption of highly conformal VMAT flank irradiation for WT was associated with low rates of both in-field and out-field relapse and was not associated with an increase in local failure. This study adds further evidence to support the widespread adoption of highly conformal flank irradiation as the standard of care for WT. References: T.Ali, M.Khan, et al. Evaluating Potential Dosimetric Advantage of Integrating Highly Conformal Target Delineation with VMAT Compared to Conventional Flank Irradiation for Wilms Tumors. Inter Jour of Radiation Oncol Bio Physics. 2025. Mul J, van Grotel M, Seravalli, E Bosman ME, et al. Locoregional control using highly conformal flank target volumes and Volumetric-Modulated Arc Therapy in pediatric renal tumour: results from the Dutch national cohort.Radiother Oncol. 2021. Mul J, Seravelli E, Bosman ME, et al. Estimated Clinical Benefit of combining Highly Conformal Target Volumes with Volumetric Arc Therapy (VMAT) versus Conventional Flank Irradiation in Pediatric Renal Tumours.Clinical and Translational Radiation Oncol. 2021 Keywords: Flank irradiation, VMAT, Wilms tumour
Outcomes after proton beam therapy for childhood rhabdomyosarcoma of the pelvis Benjamin F.B. Mayer 1 , Sabine Frisch 2 , Yi-Lan Lin 2 , Sandija Plaude 2 , Andreas Schmidt 1 , Martin Ebinger 3 , Jörg Fuchs 1 , Beate Timmermann 2 1 Paediatric Surgery and Paediatric Urology, Children's University Hospital, Tübingen, Germany. 2 West German Proton Therapy Center, University Hospital, Essen, Germany. 3 Paediatric Hematology, Oncology, Gastroenterology, Nephrology and Rheumatology, Children's University Hospital, Tübingen, Germany Purpose/Objective: The treatment of pelvic rhabdomyosarcoma (RMS) involves chemotherapy with tumor resection and/or radiotherapy. Due to its proximity to neighbouring organs at risk, local treatment poses a significant challenge. Proton beam therapy (PBT) is favoured as the radiotherapy modality of choice because it reduces toxicity to the target organ and surrounding tissues. This study investigated the oncologic and functional outcomes of PBT for pelvic RMS, as well as the differences in outcomes between local treatment strategies. Material/Methods: A single-center study of children with RMS of the bladder/prostate, pelvis or lower retroperitoneum enrolled in a prospective registry (DRKS00005363) was conducted. Exclusion criteria were previous radiotherapy, relapsed or metastatic RMS, FOX01 fusion-positive RMS, tumors with a diameter smaller than 5 cm at diagnosis with negative lymph node status and unavailability of follow-up data. Adverse events (AEs) were classified according to CTCAE V4. Results: Between 2012 and 2022, 31 children (12 girls and 19 boys) received PBT for pelvic RMS. The median age at PBT was 49 months (range 19 – 182). PBT was performed as definitive local treatment (n=15) and in combination with tumor resection (n=16), respectively. The median total dose was 55.8 Gy (range 41.1 – 59.4) in the definitive PBT group and 50.4 Gy (range 41.1 – 55.8) in the combined local treatment group. Severe acute AEs were observed in 11 patients with grade IV anemia, in 10 patients with grade III neutropenia and in 9 patients with grade III dermatitis. All acute AEs were reversed 3 months after PBT. The median follow- up (FU) time was 44 months (range 5-117). The mean 4-year overall survival was significantly higher in the combined local therapy group than in the definitive PBT group (45.7 vs. 36.5 months, p=0.019). However, there was no statistically significant difference in the mean 4-year progression-free survival between the two groups (41 vs. 39.3% months, p=0.141). During FU, the bladder had been preserved in 12/15 patients in
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