ESTRO 2021 Abstract Book

S1373

ESTRO 2021

An evident trend of diminishing thickness in LAT-LAT incidence was observed for all patients, with a mean value of -1.3±0.7 cm at treatment end for not-replanned patients. Replanned patients showed an evident thickness variation at the time of replanning decision, having measured values at least a standard deviation below the mean value of the not-replanned patients.

Conclusion Since patient’s overall weight loss is not a good candidate for driving the decision to replan [1], simple parameters should be adopted to help radiation oncologists in this decision. A sinogram-base method to evaluate inter-fraction thickness variation of irradiated tissue can be a potential metric for replanning decision. Anyway, further investigation and a wider number of patients should be considered for determine its effectiveness. [1] Radiol Med 2012 117:885-891 PO-1654 Quality Assurance of C-Arm CBCT Angiography for Stereotactic Radiation Surgery J.A. Fermoso Gutiérrez 1 , R. Rodríguez Romero 1 , X. Pifarré Martínez 1 , J. Martínez Ortega 1 , J. Ruiz Martín 1 , A. Gómez Gascón 1 1 Hospital Universitario Puerta de Hierro Majadahonda, Servicio de Radiofísica y Protección Radiológica, Majadahonda, Spain Purpose or Objective Stereotactic radiation surgery is one of the therapeutic modalities currently available to treat cerebral arteriovenous malformations. Conventionally, digital subtraction angiography using orthogonal x-rays are used to identify the target volume for SRS treatment, but often 2D images are not compatible with the treatment planning systems (TPS). The purpose of this study was to evaluate the image quality of a C-arm cone beam computed tomography (CBCT) comparing it with a CT simulator image. Materials and Methods CBCT images were acquired using an Allura Xper FD20 ( Philips ) angiograph, and compared with those obtained from an Aquilion LBTSX-201 A ( Toshiba ) CT simulator . The spatial distortion of CBCT was evaluated by analyzing the images of a Lucy ( Standard Imaging) phantom displaced from the center of rotation with the following configuration: a radiopaque grid (Fig. 1a), and four equispaced peripheral cylinders with radiopaque markers inside.