ESTRO 2022 - Abstract Book

S89

Abstract book

ESTRO 2022

Conclusion An echogenic surface coating reduced reverberation artifacts and improved needle visibility when brachytherapy needles were implanted at an angle to the ultrasound probe or in the presence of B-mode signal degradation. The results are consistent with the hypothesis that a microsphere coating can redirect ultrasound waves to improve needle visibility when the signal-generating ultrasound waves impinge nonparallel to the transducer. Testing is ongoing within a cadaverous male pelvis.

OC-0115 Monte Carlo study of high atomic number inorganic scintillators for Ir-192 BT in vivo dosimetry

V. Kaveckyte 1,2 , E. Buch Jørgensen 3,4 , J. Graversen Johansen 3,4 , Å. Carlsson Tedgren 1,5,6

1 Linköping University, Department of Health, Medicine and Caring Sciences, Linköping, Sweden; 2 Copenhagen University Hospital - Rigshospitalet, Department of Oncology, Copenhagen, Denmark; 3 Aarhus University, Department of Clinical Medicine, Aarhus, Denmark; 4 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 5 Karolinska University Hospital, Department of Medical Radiation Physics and Nuclear Medicine, Stockholm, Sweden; 6 Karolinska Institute, Department of Oncology-Pathology, Stockholm, Sweden Purpose or Objective High atomic number ( Z ) inorganic scintillators have properties suitable for 192 Ir BT in vivo dosimetry. Compared to organic scintillators, they have greater light output and negligible stem-effect. However, high Z leads to larger absorbed-dose energy dependence which requires thorough characterization. Up to now, experimental determination is prevalent though measurement accuracy can be compromised by steep dose gradients. Additionally, the measured signal may be convolved with other detector response artifacts that are not accounted for. Monte Carlo (MC) circumvents such problems and allows for broader investigation of factors affecting the absorbed-dose energy dependence of detectors under clinically relevant conditions. Therefore, aiming to improve in vivo dosimetry accuracy, three inorganic scintillators, which have been used in practice and have suitable luminescence properties, were characterized with MC in this study. Materials and Methods The focus was on ZnSe ( Z =32), and for comparison, CsI ( Z =54) and Al 2 O 3 ( Z =11) were included. A general-purpose MC code PENELOPE was used to evaluate detector absorbed-dose energy response relative to water and its dependence on scatter conditions (full and patient-like), as well as patient anatomy (pelvic bones and prostate calcifications). Results ZnSe and CsI overresponded substantially compared to water in a patient-like phantom, but the normalized curves, which would correspond to the absorbed-dose energy correction, did not differ between the two media despite large difference in their atomic numbers (Fig. 1). Under full-scatter conditions, ZnSe response increased by 10% at 5 cm compared to limited scatter conditions, whereas the response of Al 2 O 3 did not depend on phantom size. Pelvic bones did not affect ZnSe response in a mimicked prostate treatment. However, it decreased by 2% when an intermediate-size calcification was between the source and the detector. Finally, comparison with high-precision experimental data of ZnSe:O response showed good agreement with the MC results (Fig. 2).