S509
Clinical - Haemotology
ESTRO 2026
and red DVHs in Figure 2). VMAT slightly increased Dmean to lenses and to PTV with median (min, max) 4.1% (-3.6%,12.9%,p=0.05) and 5.4% (0.9%,10.0%,p=0.004), respectively (Figure 2). PTV V110%<8% was met by all IMRT plans and six of nine VMAT plans, while PTV V120%<3% was met by all IMRT plans and seven of nine VMAT plans.
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Total body irradiation: VMAT considerably reduces dose to kidneys and lungs compared to step and shoot IMRT at extended SSD Isak Wahlstedt 1 , Aleksandra Caranovic 1 , Tim E Berlon 1 , Lisa M Frederiksen 1 , Katrin E Håkansson 1 , Rebecca J Tobin 1 , Ivan R Vogelius 1,2 , Mogens Bernsdorf 1 1 Department of Oncology, Centre for Cancer and Organ Diseases, Copenhagen University Hospital - Rigshospitalet, Copenhagen, Denmark. 2 Department of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark Purpose/Objective: Recently, Hui et al.[1] showed that reduced dose to kidneys and lungs with VMAT compared to 2D-TBI translated into significantly reduced related side effects while retaining the same treatment efficacy. We are currently using an extended SSD step and shoot IMRT technique [2] which is more advanced than the 2D-TBI technique investigated by Hui et al.[1]. We investigated if we could reduce the dose to lungs, kidneys, and lenses without compromising PTV coverage with (i) our current clinical IMRT technique and (ii) using a publicly available VMAT-TBI script [3]. Material/Methods: We included nine patients - the three most recent pediatric (<18years), three most recent female adults ( ≥ 18years), and three most recent male adults treated with myeloablative regimens (12 Gy in 6 fractions) in our clinic. First, an experienced TBI dose planner re- planned our clinically delivered IMRT plans to achieve as low Dmean to lungs, kidneys, and lenses as possible. Second, we generated VMAT plans with the same aims using a publicly available script for VMAT- TBI dose planning in Eclipse (Varian Medical Systems) [3]. We normalized all plans to PTV D98%=90% and strived to achieve PTV V110%<8% and PTV V120%<3%. PTV was defined as PTV = (body- 5mm)-(lungs+3mm)-(kidneys+3mm)-(lenses+3mm). We compared doses achieved with IMRT and VMAT based on Dmean to PTV, kidneys, lungs, and lenses as well as on DVHs of the same structures. We evaluated differences in Dmean achieved with re-planned IMRT and VMAT with Wilcoxon signed-rank tests. Results: Patient ages (years) were 9, 10, and 15 (pediatric), 18, 39, and 50 (female), and 20, 41, and 52 (male). VMAT reduced Dmean to kidneys with median (min, max) 11.4% (3.6%,23.8%,p=0.004) and Dmean to lungs with 17.7% (1.5%,34.3%, p=0.004) compared with re- planned IMRT (Figure 1 and 2). Largest Dmean reductions to kidneys and lungs were seen for pediatric patients (orange symbols in Figure 2D and F). Re-planned IMRT only slightly reduced doses to lungs and kidneys compared to clinical IMRT plans (green
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