ESTRO 2023 - Abstract Book

S1528

Digital Posters

ESTRO 2023

A.I. Milanes Gaillet 1 , G. Pozo Rodriguez 1 , P. Adaimi 1 , E. Cabello Murillo 2 , R. Diaz Fuentes 1 , A. Gaitan Simon 1 , M. Manzano Rodriguez 2 , P. Botella 3 , A. Ferrando 1 , D. Rojo Navarrete 1 , I. Alonso Delgado 3 , D. Martin Garcia 3 , V. Trapaga Porrero 3 , R. Rollan Plaza 3 , R. Brazales 1 , A. Ruiz Alonso 3 , J.F. Perez-Regadera 3 1 Hospital Universitario 12 de Octubre, Radiotherapy Oncology, Madrid, Spain; 2 Hospital universitario 12 de Octubre, Radiotherapy Oncology, Madrid, Spain; 3 Hospital 12 de Octubre, Radiotherapy Oncology, Madrid, Spain Purpose or Objective Stereotactic body radiation therapy (SBRT) is an established treatment modality in the management of early-stage nonsmall cell lung cancer. Techniques have evolved to achieve faster treatments using Volumetric modulated arc therapy (VMAT). In addition, with the use of flattening filter free beam (FFF) instead of a traditional flattened filter beam (FF) allow higher rates to be used. With this study we will compare whether treatments with FFF beams are really faster compared to treatments with FF beams. Materials and Methods A total of 42 patients were selected for the study. Imaging of each patient consisted of a 2 mm slice thickness CT scan. Compression abdominal was used to reduce ITV margin generated with ten phases. For each patient, two different treatment plans were calculated in Eclipse v.15.6 TPS (Varian Medical Systems. Palo Alto, CA) one using 6MV for Varian Clinac IX linac with maximum dose rate of 600 MU/min with filter beams and the other with 6MV FFF Varian Halcyon v.2 of 800MU/min. The Anisotropic Analytical Algorithm (AAA) was used with the Progressive Resolution Optimizer (v 15.6) for VMAT optimization. The prescription was 60 Gy to the PTV in 8 fractions (7.5 Gy per fraction). The isocenter position was set to the geometric center of the PTV and with three half rotations arcs and collimator angles of 30°, 330° and 30° as shown in Figure 1.

The clinical Clinac VMAT and Halcyon VMAT plans were calculated with same constrains optimizations.

Results In each case, MU was adjusted to get the same target coverage. In some patients it was necessary more MU for Clinac VMAT plan but in others, Halcyon VMAT calculated more MU as shown in Table 1. In this table, each point represents one patient calculated in two different plans for Clinac IX and Halcyon v.2. No significant differences exist (p>0.05).

Conclusion The result of this study indicates that treatments of lung SBRT patients on Halcyon is so effective and similar than on Clinac IX linac. However Halcyon have higher MU rate than Clinac IX, so treatments on Halcyon are slighter faster but with no