ESTRO 2021 Abstract Book

S1318

ESTRO 2021

Conclusion This work provides an end to end test which ensures that the TPS is correctly calculating dose, and that the new source (10Ci nominal activity) has been correctly entered into the TPS and afterloader software. The afterloader dwell scaling is verified with correct measurements of absolute dwell times and source positions. This procedure has been embedded efficiently in the post-exchange quality assurance of the unit. The dose formalism described by using a cross-calibrated micro-ionization chamber is novel and was not found elsewhere in literature, accounting on the advantages of using a dosimeter of this nature. PO-1595 Patient-Specific QA of single-isocenter multitarget SRS using the OCTAVIUS® detector 1600 SRS J. Calvo-Ortega 1 , S. Moragues-Femenia 1 , C. Laosa-Bello 1 , M. Pozo-Massó 1 , J. Casals-Farran 1 1 hospital Quirónsalud Barcelona, Radiation Oncology, Barcelona, Spain Purpose or Objective To establish the action levels for pre-treatment QA of single-isocenter multiple brain metastasis stereotactic radiosurgery (SRS) plans using a new 2D detector array. Materials and Methods The Octavius 4D Modular Phantom (O4D) with Top SRS plus phantom. Fifteen clinically treated SIMT SRS plans were retrospectively included in this study. Number of lesions per plan ranged from 2 to 6 (median: 2), with a median volume of 1.5 cm 3 . Distance from target center to treatment isocenter ranged from 1.7 to 6.2 cm (median: 6.2 cm). Plans were designed with the Eclipse TPS (AAA v 10.0.28, 1 mm calculation grid size) using non-coplanar IMRT technique, and delivered using 6 MV photons from a Varian Clinac 2100 CD linac with a Millennium 120 MLC. Each clinical SRS plan was recalculated on the Top SRS plus phantom synthetically created in the Eclipse. From the measurements taken by the 2D array for the different beam incidences of the SRS plan, the PTW Verisoft software (v 8.0.0164) reconstructs the 3D dose within a cylindrical region of 15 cm-diameter contained by the Top SRS plus phantom. Dose reconstruction with 1 mm voxel size was selected in Verisoft. Eclipse and