ESTRO 2022 - Abstract Book

S1395

Abstract book

ESTRO 2022

Conclusion Our results on patient data suggested the possibility of reducing the CT dose for the purpose of dose calculation during the course of treatment. An aggressive dose reduction by a factor of up to 10 did not have a significant effect on the dose distributions. A quantitative analysis utilizing more patient data is ongoing.

PO-1608 Application of BioXmark® liquid fiducial markers for CyberKnife® stereotactic body radiotherapy

I. Surkova 1 , G. Boka 1 , M. Me ž eckis 1 , S. Ledi ņ a 1 , V. Buryk 1

1 Radiosurgery Centre Sigulda, Radiation Oncology, Sigulda, Latvia

Purpose or Objective Robotic stereotactic body radiotherapy (SBRT) has the benefit of automatic tracking of moving targets. Fiducial markers are essential for multiple target locations, but implantation of fiducials are linked with risk of complications. The BioXmark ® is a novel liquid based fiducial marker which might be implanted with a very thin needle reducing possible risk of complications. Earlier BioXmark has been tested for image guided radiotherapy with conventional linear accelerators, but has not yet been tested for automatic tracking with CyberKnife ® robotic SBRT systems. The purpose of this study is to compare BioXmark ® and current standard solid gold fiducial markers in CyberKnife ® tracking system, in order to evaluate correction precision during the CyberKnife ® stereotactic body radiotherapy (SBRT). Materials and Methods BioXmark ® fiducials (Nanovi A/S, Lyngby, Denmark) were prepared in vitro with following volumes 50 µL, 100µL, and 200 µL and cooled to acquire stability of the markers. 4 fiducials of each size were placed and sealed in custom-made inserts according to Accuray recommendations ( ≥ 20mm from each other). Following inserts were placed in the anthropomorphic E2E head and neck phantom (Cetacea ® , California, USA) with built-in standard gold markers. Three experimental treatment plans with every fiducial size were made with 3 image centers and 8 fiducials in each (4 built in standard gold fiducials and 4 test fiducials). Measures were made in 3 different phantom positions and systems proposed corrections were recorded. The average value of linear, rotational offsets and “uncertainty” parameters were assessed to characterize accuracy. Significant difference between BioXmark ® and reference gold fiducials was considered as ≥ 0.5mm in translations and ≥ 0.5 deg in rotations (W. Kilby et al. 2010).