ESTRO 2023 - Abstract Book

S1593

Digital Posters

ESTRO 2023

Purpose or Objective Intraoperative radiation therapy (IORT) can be used to locally apply radiation doses to surgical cavities of resected brain metastases and glioblastoma. The miniaturized linear accelerator INTRABEAM 600® (Carl Zeiss Meditec AG, Oberkochen, Germany) offers a low-energy system of 50kV X-rays. To date, placing the spherical applicator in the surgical bed has been done manually and without final positioning verification. Ultimately, without positional control, it must be assumed that the applicator is optimally positioned against the tissue in the tumor cavity, without any air interference or fluid underlying. Misplacements could lead to incomplete dose delivery, potentially yielding an increased risk of recurrence. Therefore, we deemed relevant to assess intraoperative imaging as a novel option for easing the applicator positioning. Materials and Methods A surgical environment was mimicked in two test runs with an interdisciplinary team, accounting for operating and anesthesia times. The IORT planning software Radiance (GMV Innovating Solutions, Madrid, Spain) was previously calibrated with a “cheese” phantom, using twelve different density levels from 0.3 to 1.842 g/cm3, yielding a value-to-density table with -600 to +600 HU range. Furthermore, two inserts were placed in the phantom to evaluate the quality and spatial resolution of the cone-beam CT (CBCT) imaging. The O-Arm System (Medtronic, Minneapolis, MN, USA) was employed for acquiring tomographic intraoperative imaging, once the applicator was placed in a skull-shaped phantom. Two expert radiation oncologist contoured the acquired dataset and performed the treatment calculations, based on a 30 Gy prescription dose.

Fig 1. Head phantom, stereotactic device and O-arm system, mimicking a real surgical scenario.

Fig 2. Density tables acquired with the O-arm system, importen to Radiance for Monte Carlo planning