S2032
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
1 Radiation Oncology, Abderrahmen Mami Hospital, Ariana, Tunisia. 2 Faculty of Medecine of Tunis, Tunis El Manar University, Tunis, Tunisia Purpose/Objective: We aimed to evaluate and compare the dosimetric impact of VMAT versus 3D conformal radiotherapy on cardiacsubvolumes in patients with left-sided breast cancer treated with hypofractionated radiotherapy including a simultaneous integrated boost (SIB). Material/Methods: Data from 22 patients with left-sided breast cancer planned for hypofractionated radiotherapy were retrospectively analyzed. Treatment included 40 Gy in 15 fractions to the whole breast with a simultaneous integrated boost (SIB) of 48 Gy in 15 fractions to the tumor bed. For each patient, two plans were generated: 3D conformal RT (two tangential beams ± subclavicular field) and cardiac-optimized VMAT. Cardiac subvolumes—including ventricles, atria, and coronary arteries were contoured according to Duane’s cardiac atlas, and dose-volume metrics (Dmean, Dmax, V5–V40) were extracted. Paired comparisons between 3D and VMAT plans were performed using paired t-tests or Wilcoxon signed- rank tests, with evaluation of target coverage and adherence to cardiac dose constraints per DEGRO recommendations. Results: In our cohort of 22 patients with left-sided breast cancer treated with hypofractionated radiotherapy (40 Gy/15 fractions to the whole breast, 48 Gy/15 fractions SIB to the tumor bed), VMAT provided substantial reductions in cardiac exposure compared with 3D conformal radiotherapy. The most pronounced benefit was observed in the interventricular anterior artery (IVA), where Dmean decreased from 2.69 ± 0.43 Gy with 3D conformal RT to 0.13 ± 0.57 Gy with VMAT, corresponding to a mean difference of − 2.56 Gy (p<0.001). Similarly, high-dose volumes were markedly reduced: V15Gy decreased from 15.46 ± 4.44% to 0.05 ± 0.002% (p<0.001), V20Gy from 50.29 ± 0.85% to 14.12 ± 3.76% (p<0.001), and V30Gy from 39.04 ± 13.35% to 11.74 ± 3.25% (p<0.001).Global heart dosimetry also improved significantly with VMAT. Mean heart dose decreased from 3.50 ± 1.95 1.16 ± 0.29 (p=0,01), while high-dose volumes such as Heart V35 were reduced from 5.69 ± 2.05 Gy to 3.48 ± 0.49 Gy (p=0.033). Lower dose metrics, including Heart V8 and V16, were also significantly decreased, confirming that VMAT can effectively spare the heart across a wide dose range. For the left ventricle, V5Gy was significantly reduced from 27.79 ± 5.21 to 16.89 ± 8.25 (p=0.005), whereas differences in V10Gy and V23Gy were not statistically significant.(Table1)
Conclusion: In hypofractionated left breast radiotherapy with a SIB, VMAT provides superior sparing of the heart and critical subvolumes compared with 3D conformal RT. Nevertheless, 3D conformal RT can achieve satisfactory dosimetric outcomes, and the optimal technique should be individualized based on patient anatomy and cardiac risk factors. Keywords: Simultaneous integrated boost, Breast Cancer dose calculation evaluation in patient on a c-arm linear accelerator with advanced cone-beam computed tomography Kenneth W Gregg 1 , Theodore Arsenault 1,2 , Sagar Regmi 1 , Kyle OCarroll 1 , Beatriz Guevara 1 , Meiying Xing 1 , Runyon Woods 1 , Atefeh Rezaei 1 , Rojano Kashani 1,3 , Lauren Henke 1,3 , Alex Price 1,3 1 Department of Radiation Oncology, University Hospitals Seidman Cancer Center, Cleveland, USA. 2 Department of Biomedical Engineering, Case Western Reserve University, Cleveland, USA. 3 School of Medicine, Case Western Reserve University, Cleveland, USA Purpose/Objective Technical innovations in advanced CBCT demonstrate higher precision in CT number over prior systems, showing promise for accurate dose calculation with inhomogeneity correction. Direct CBCT dose calculation could enable efficient workflows not previously available on C-arm systems, enhancing patient care experience and reducing barriers to healthcare. This early in-patient study investigates dose calculation accuracy on TrueBeam v4.1 CBCT equipped with the HyperSight imaging solution (HSTB- CBCT). Material/Methods Digital Poster 5147 High-quality research images (>120kV, >670mAs) were acquired for 37 patients enrolled in IRB-approved trial NCT05975619 on HSTB-CBCT and reconstructed using
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