S1796
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
cm on each arc to allow full MLC modulation. Two arcs were set with a 30-degree collimator angle, one with the X1-jaw closed to get an X-jaw aperture of 14 cm, while the X2-jaw was closed in the other arc to get an X-jaw aperture of 14 cm. The other 2 arcs were set with a collimator angle of 330 degrees and the same X1/X2 setting as before. A pseudo-skin flash based on a virtual bolus method was used during plan optimization.2All treatment plans were optimized to achieve D95% > 95% and D2% < 107% for each PTV and to meet our institutional OAR dose constraints. A retrospective analysis of these plans was performed to investigate the achievability of the OAR dose constraints (see Table) reported by De Rose et al.1 Results: The Table shows the metric values and compliance rates for each OAR constraint. The contralateral breast and liver were the organs where the recommended dose constraints were most frequently unfulfilled (in 9 and 5 plans, respectively).
Conclusion: The use of the stoichiometric CT number calibration curve improves the accuracy of the dose calculation. References: 1 Med Phys. 2020 Apr;47(4):1509-1522.2 Med Phys. 2024 Mar;51(3):1571-1582. Keywords: CT, stoichiometric, calibration
Digital Poster 58
A retrospective analysis of the achievability of recommended dose constraints in VMAT plans for breast cancer plus regional nodes irradiation CORAL LAOSA-BELLO 1 , JUAN-FRANCISCO CALVO- ORTEGA 1,2 , MARIA-DEL-CARMEN ARANDA-QUINTERO 2 1 RADIATION ONCOLOGY, HOSPITAL QUIRÓNSALUD BARCELONA, BARCELONA, Spain. 2 RADIATION ONCOLOGY, HOSPITAL QUIRÓNSALUD MÁLAGA, MÁLAGA, Spain Purpose/Objective: To analyze VMAT plans designed for breast cancer plus regional nodes irradiation (RNI) by evaluating the compliance with recently published organ-at-risk (OAR) dose constraints.1 Material/Methods: The first 16 patients (7 right-sided, 9 left-sided) receiving postoperative radiotherapy for breast cancer plus RNI in our department were included. Treatment plans were designed with the Varian Eclipse treatment planning system (Acuros XB v. 16.1 algorithm, dose-to- medium), using 6 MV photon beams from a Varian TrueBeam linac equipped with the High Definition MLC. Prescription dose was 40.05 Gy in 15 fractions for the breast and the regional nodes (PTV40.05) ± a simultaneous integrated boost of 48 Gy for the tumor bed (PTV48). The plans consisted of 4 VMAT arcs and a single-isocenter. The gantry angles ranged from about 181/50 degrees to about 310/179 degrees for right- /left-sided cases. The Eclipse Arc Geometry tool was used to try to encompass the whole target (breast plus regional nodes) with the jaws. The whole target was partially outside the beam's-eye-view in some projections of each arc. The “flip-flop” technique was used such that the X-jaw aperture was limited to 14
Conclusion: Our analysis revealed that the liver and the
contralateral breast should be spared the most to meet the dose constraints recommended by De Rose et al.1 We think that these recommendations can be used as a benchmark for self-auditing the institutional OAR dose constraints of radiotherapy departments. References: 1 Radiother Oncol. 2024 Oct 19:202:110591. 2 J Appl Clin Med Phys. 2018 Sep;19(5):463-472. Keywords: constraints, OAR, VMAT Validation of a freely available Eclipse script for automatic calculation of EQD2 dose distribution in external beam radiotherapy JUAN-FRANCISCO CALVO-ORTEGA 1,2 , CORAL LAOSA- BELLO 1 , SANDRA MORAGUES-FEMENIA 1 1 RADIATION ONCOLOGY, HOSPITAL QUIRÓNSALUD BARCELONA, BARCELONA, Spain. 2 RADIATION ONCOLOGY, HOSPITAL QUIRÓNSALUD MÁLAGA, MÁLAGA, Spain Digital Poster 67 Purpose/Objective: We present the validation of an Eclipse script designed to streamline equivalent dose in 2 Gy fractions (EQD2) calculations for external beam radiotherapy (EBRT). Material/Methods: The Eclipse v. 16.1 treatment planning system (Varian
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