ESTRO 2022 - Abstract Book

S88

Abstract book

ESTRO 2022

Conclusion Previously published methods of dwell time determination can also be applied on a moving phantom, with a similar accuracy of <0.1s. Time resolved dosimetry using an IP and 3D camera allows for distinguishing between internal and external motion, providing information on dwell times even when the phantom is moving. Consequently, it is expected that this system could differentiate between external patient movement and source movement, and thus improve in vivo dosimetry for HDR BT.

OC-0114 Improving brachytherapy needle ultrasound conspicuity with an echogenic coating

E. Brost 1 , B. Stish 1 , C. Deufel 1

1 Mayo Clinic, Department of Radiation Oncology, Rochester, USA

Purpose or Objective This study was aimed at improving the conspicuity of titanium high-dose rate (HDR) brachytherapy needles under B-mode ultrasound imaging by applying a commercially available echogenic surface coating (Sono-Coat™, Encapson, Netherlands). The echogenic coating was intended to improve needle visualization within regions of signal degradation that can occur during prostate or gynecological HDR brachytherapy. Sono-Coat™ is a commercial product designed to improve ultrasound visibility, particularly when imaging objects which are nonparallel to the ultrasound transducer. Materials and Methods 17-gauge, 25 cm titanium HDR brachytherapy needles (Varian Medical Systems, USA) were coated with Sono-Coat™, a coating composed of acoustically reflective microspheres, over a 2 cm region starting from the needle tip. Three coatings of variable thickness: M2 (25 um thickness), M3 (40 um), and M5 (64 um) were compared against an uncoated control needle. The coated and uncoated needles were imaged using B-mode ultrasound in a CIRS tissue equivalent prostate phantom (CIRS Inc., USA) with a bk3000 (BK Medical, USA) unit and E14CL4b transrectal probe. Needle conspicuity was assessed under three conditions: a single needle implant, an implant with multiple needles between the probe and the needle of interest, and an implant with simulated rectal gas. The simulated rectal gas was introduced into images through taping medical gauze to the ultrasound probe surface then wrapping the probe with a condom. All images were assessed qualitatively for needle visibility and the presence of artifacts. Results Under ideal geometry, where the needle is implanted parallel to the transrectal probe, the control needle and microsphere coated needle were equally visible (Figure 1, top panels). The microsphere coated needles produced noticeably less reverberation artifact and appeared as a contiguous object, whereas the control needle imaged as a bifurcated object along the body of the needle. When the angle of incidence between the needle and probe was increased, the visibility of the microsphere-coated needle was noticeably better than the control needle (Figure 1, bottom panels). In the rectal gas simulation (Figure 2), the microsphere coating improved visibility into a region of signal degradation, an effect that may be attributed to the redirection of ultrasound waves by the microspheres from non-void regions towards the probe.