ESTRO 2025 - Abstract Book

S1636

Clinical – äediatric tumours

ESTRO 2025

2960

Digital Poster Estimated benefit of IMPT compared to VMAT for highly conformal flank target irradiation in pediatric renal tumors Fasco van Ommen 1 , Shermaine Pan 2 , Mirjam Willemsen-Bosman 1 , Louise Dawdall 3 , Sarah Tweedly 3 , Marianne C. Aznar 4 , Matthew Lowe 3,4 , Ed Smith 2,4 , Enrica Seravalli 1 , Marry M. van den Heuvel-Eibrink 5 , Geert O. Janssens 1,5 1 Department of Radiation Oncology, University Medical Center Utrecht, Utrecht, Netherlands. 2 Department of Clinical Oncology, The Christie NHS Foundation Trust, Manchester, United Kingdom. 3 Christie Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, United Kingdom. 4 Division of Cancer Sciences, University of Manchester, Manchester, United Kingdom. 5 Pediatric Oncology, Princess Máxima Center for Pediatric Oncology, Utrecht, Netherlands Purpose/Objective: An increasing number of pediatric patients with renal tumors across SIOP-RTSG-affiliated countries are treated with highly conformal flank target volumes mainly by Volumetric-Modulated Arc Therapy (VMAT) treatment plans. Given the increasing access to proton therapy, this in silico study aims to estimate the dosimetric benefit, in terms of dose constraint violations, of highly conformal flank target volumes with IMPT compared to VMAT for pediatric patients with renal tumors. Material/Methods: Ten consecutive cases with a left-sided renal tumor (median age: 4.5 years) were selected. For each case, a VMAT and IMPT plan was made for an intermediate risk (IR; 14.4/1.8 Gy/#) and high-risk (HR; 25.2/1.8 Gy/#) prescription dose (PD). The treatment plans were analyzed for coverage of target volumes (ITV: D99% > 95% PD; PTV/OTV: D98% > 95% PD and D2% < 107% PD), and to compare dose constraints of the contralateral kidney (Dmean < 8Gy; priority 1), vertebrae (left-right and anterior-posterior gradients for 0-2 years < 3 Gy and ≥3 years: < 5 Gy; priority 2), heart, spleen, pancreatic tail and liver (Dmean < 10 Gy; priorities 3-5;7), bowel (Dmean < 20 Gy; priority 6) and mammary glands (Dmean < 1 Gy; priority 8). Results: Target coverage was achieved and similar for both PDs and techniques. For IR and HR PDs, dose constraints to the vertebrae, heart, bowel and liver were met for all patients with both VMAT and IMPT. For IR PDs, constraint violations for cases treated with VMAT vs IMPT were respectively observed for the spleen (2/10 vs 2/10), pancreatic tail (5/10 vs 3/10) and mammary glands (1/10 vs 0/10). For HR PDs, constraint violations with VMAT vs IMPT were respectively observed for the contralateral kidney (0/10 vs 1/10), spleen (7/10 vs 6/10), pancreatic tail (10/10 vs 10/10) and mammary glands (5/20 vs 0/20). The absolute dose constraint violations were minimal for the contralateral kidney and mammary glands, but not for the spleen and pancreatic tail (Table 1).