S2759
RTT - RTT contouring, target definition, and treatment planning
ESTRO 2026
(MU/cGy) was reported.2
Digital Poster 26 Dosimetric analysis of nodal breast VMAT using a High-Definition MLC CORAL LAOSA-BELLO 1 , MARÍA-DEL-CARMEN ARANDA- QUINTERO 2 , JUAN-FRANCISCO CALVO-ORTEGA 1,2 1 RADIATION ONCOLOGY, HOSPITAL QUIRÓNSALUD BARCELONA, BARCELONA, Spain. 2 RADIATION ONCOLOGY, HOSPITAL QUIRÓNSALUD MÁLAGA, MÁLAGA, Spain Purpose/Objective: The Varian High-Definition (HD) MLC only allows a maximum MLC field size of 22 cm in the cranio-caudal patient's direction. Therefore, a single-isocenter half- beam technique is not permissible to treat a large target such as breast/chest with lymph node involvement. We aim to report our experience using this type of MLC and the VMAT technique for this clinical situation. Material/Methods: The first 16 patients (7 right-sided, 9 left-sided) receiving postoperative radiotherapy for breast cancer plus regional nodes in our department were included. The treatment plans were designed with the Varian Eclipse treatment planning system (Acuros XB v. 16.1, dose-to-medium), using 6 MV photon beams from a Varian TrueBeam linac equipped with the HD MLC. The prescription dose to the breast and the regional nodes (PTV40.05) was 2.67 Gy in 15 fractions. A simultaneous integrated boost of 48 Gy was prescribed for the tumor bed (PTV48).The plans consisted of 4 arcs and a single-isocenter, with the gantry running from about 181/179 degrees to about 50/310 degrees (Varian IEC scale) for right-/left-sided cases. The Eclipse Arc Geometry tool was used to try to cover the whole PTV with the jaws of each arc. However, it was partially outside in the beam's-eye-view in some projections of each arc (Figure). To allow full MLC modulation, the “flip-flop” technique was used such that the X-jaw total aperture was kept at ≤ 14 cm on each arc. Two arcs were set with a collimator angle of 30 degrees and the X1-jaw and X2-jaw were closed in the first and second arc, respectively, such that the X-jaw total aperture was ≤ 14 cm for each arc. Collimator angle of 330 degrees was set in the other two arcs, and the same X1/X2 adjustments as described before were done. During plan optimization (Varian Photon Optimizer v. 16.1), the aperture shape controller strength was set to “low” and a pseudo skin flash based on a virtual bolus method was used.1The planning aim was to achieve our departmental target objectives and organ- at-risk (OAR) constraints (Table). Analysis of the dosimetric results was conducted, included patient specific QA (PSQA) results. PSQA was performed using the PTW Octavius 4D system. Complexity plan
Results: See Table
Conclusion: The single-isocentric VMAT planning technique using the HD MLC resulted in acceptable target dosage and OAR protection. Despite the high plan complexity (> 3 MU/cGy),3 PSQA ensured the accuracy of this technique. References: 1 J Appl Clin Med Phys. 2018 Sep;19(5):463-472.2 Br J Radiol. 2019 Jul 24;92(1102):20190270.3 Adv Radiat Oncol. 2024 May 6;9(8):101535. Keywords: breast, VMAT, high-definition
Digital Poster 32
Comparison of non-flattened vs. flattened beams for ultra-hypofractionated breast radiotherapy CORAL LAOSA-BELLO 1 , JUAN-FRANCISCO CALVO- ORTEGA 1,2 , María-del-Carmen Aranda-Quintero 2 , Marcelino Hermida-López 3
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