ESTRO 2023 - Abstract Book

S1486

Digital Posters

ESTRO 2023

Figure 1: Heat maps showing the sensitivity of the various metric combinations to lateral and longitudinal inaccuracies with the Alderson phantom for the 3D and IMRT plans.

Conclusion The SunCHECK platform was systematically evaluated and has been successfully implemented for clinical QA of radiotherapy deliveries in our clinic. The 2 % / 2 mm metric was shown to be sensitive enough to detect positional inaccuracies in the Alderson phantom investigations. Notably, a more complex phantom and more complex changes to the phantom lead to a higher sensitivity of the EIVD system. Therefore, larger DTA/DD combinations have been established by other authors in retrospective clinical studies on real patients.

PO-1765 Transit Dosimetry of SBRT with Electronic Portal Dosimetry Device in Patient with Spinal Implant

Y. Yedekci 1 , A. Elmalı 1 , G. Demirkiran 2 , G. Ozyigit 1 , G. Yazici 1

1 Hacettepe University, Radiation Oncology, Ankara, Turkey; 2 Hacettepe University, Orthopaedics and Traumatology, Ankara, Turkey Purpose or Objective In recent years, the use of the Electronic Portal Imaging Device (EPID) as an in vivo dosimeter has become widespread. However, reports of EPID for stereotactic body radiotherapy (SBRT) applications is scarce. There is no data on this topic especially when there are high-density materials in the radiation field. In this study, we aimed to investigate the dose distributions of SBRT treatment plans in patients with spinal implants by in vivo EPID dosimetry. Materials and Methods Implants were inserted in phantoms that mimic the vertebrae, and VMAT plans were created on the phantoms to deliver 16 Gy radiation doses to the target in 1 fraction. In vivo EPID measurements were performed for each irradiation. The results were compared with the treatment planning system using the gamma analysis method. Results According to the gamma analysis results, while the non-implant model met the acceptance criteria with a rate of 95.4%, the implanted models did not pass the test with results between the rates of 70% to 73%. In addition, while the dose difference in the isocenter was 1.3% for the non-implanted model, this difference was observed to be between 7% and 8% in the implanted models. Conclusion Our study revealed that EPID can be used as in vivo dosimetry for the VMAT-SBRT applications. However, unacceptable dose differences were obtained by in vivo EPID dosimetry in the VMAT-SBRT applications of patients with an implant. In the treatment of such patients, alternative treatment methods should be preferred in which the interaction of the implants with radiation can be prevented.

PO-1766 High-resolution CMOS detector array for robotic SRS treatment plan verification

K. Holm 1 , S. Erdem 1 , K. Schubert 1 , J. Krimmer 2

1 Heidelberg University Hospital, Department of Radiation Oncology, Heidelberg, Germany; 2 IBA Dosimetry GmbH, -, Schwarzenbruck, Germany Purpose or Objective Robotic stereotactic radiosurgery (SRS) is able to deliver spatially precise, very small dose distributions. To verify these complex treatment plans, a 2D dose measurement with a sufficient resolution has to be performed. For this purpose, we have examined the usability of the IBA myQA SRS array which is based on a CMOS technology as it offers a resolution of 0.4 mm with no pixel spacing.