ESTRO 2021 Abstract Book

S57

ESTRO 2021

Conclusion We presented a method that defines the application range of our DL-based dose engine, by analyzing anatomical features of a large variety of abdominal tumour patients. We used this analysis to perform a fast QA check on arbitrary MLC segments: any segments lying within the envelope can be safely handled by the dose engine, while segments located outside its boundaries are flagged by our algorithm for additional checking. Our next steps will focus on improving the specificity and complexity of our method as well as adding more features in our envelope analysis. In the near future we aim to expand the tumour sites handled by our dose engine in order to introduce it in a clinical setup for secondary dose calculations. OC-0084 Validation of a source tracking method for brachytherapy in vivo dosimetry using a realistic phantom T. van Wagenberg 1 , G. Fonseca 1 , R. Voncken 1 , C. Van Beveren 1 , F. Verhaegen 1 1 Maastricht University Medical Centre+, Department of Radiation Oncology (Maastro), Maastricht, The Netherlands Purpose or Objective Despite excellent reported clinical outcomes in different treatment sites for high-dose rate (HDR) brachytherapy (BT), the numerous manual steps in the workflow make it somewhat error prone. Due to the lack of monitoring systems, errors are often not detected and in some cases go unnoticed for years. To overcome this issue, our group is developing IrIS (Iridium Imaging System) for in vivo dosimetry (IVD) in BT that should allow for real time detection of treatment errors. IrIS tracks the source with an imaging panel (IP), by capturing gamma rays exiting the patient. This then allows for time-resolved reconstruction of the source position. In this work this method will be validated using realistic phantoms, to evaluate the sensitivity of the IP and assess its ability to reconstruct the source position. Materials and Methods To validate the source tracking method, a head phantom based on the CT scan of a patient was created with a 3D printer. The phantom was printed with multiple filaments that mimic soft tissue and bone-like materials. Radiopaque markers are attached to the phantom to allow for registration of the IP in the CT coordinate system (fig. 2a). A different set of markers with a fixed position compared to the panel is used to reconstruct the source position (fig. 2b). Realistic treatment plans with a range of dwell times (0.3-4s) in 3 catheters and interdwell distances of 0.2 cm were administered for different positions of phantom and IP to define the precision and accuracy of the method. In addition, the capability of IrIS to detect wrong dwell times, skipped dwell positions and swapped catheters was tested by simulating these errors experimentally.