ESTRO 2022 - Abstract Book

S1481

Abstract book

ESTRO 2022

1 Aichi Cancer Center, Radiation Oncology, Nagoya, Japan; 2 Aichi Cancer Center, Neurosurgery, Nagoya, Japan; 3 Shiokawa Hospital Gamma Knife Center, Radiation Oncology, Suzuka, Japan; 4 Yachiyo Hospital Radiation Therapy Center, Radiation Oncology, Anjo, Japan; 5 Aichi Medical University Hospital, Radiology, Nagakute, Japan; 6 Daiyukai General Hospital, Radiology, Ichinomiya, Japan Purpose or Objective Spine stereotactic body radiation therapy (SBRT) planning requires accurate image registration of MRI/CT-myelogram to the planning CT for spinal cord delineation. To confirm the fully automated rigid image registration (A-RIR) accuracy in postoperative spine SBRT, we conducted a multicenter non-inferiority study compared to the human registration (H-RIR). Materials and Methods Twenty-eight metastatic cancer patients who underwent postoperative spine SBRT are enrolled. All patients underwent planning CT scans in the immobilized supine position under the following conditions: field of view = 550 mm, slice thickness = 1 mm, the spatial resolution = 1.074 mm/pixel. CT-myelogram was obtained for spinal cord delineation through an intrathecal injection of iohexol contrast, followed by CT simulation. The adopted A-RIR workflow is a contour-focused algorithm performing a rigid registration by maximizing normalized mutual information (NMI) restricted to the data contained within the automatically extracted contour. The A-RIR and H-RIR were performed after an NMI-based RIR on the whole image as the baseline. Three radiation oncologists from multicenter were prompted to review two blinded registrations and choose one for clinical use. Indistinguishable cases were allowed to vote equivalent, counted A-RIR side. A-RIR is considered non-inferior to H-RIR if the lower limit of the 95% confidence interval (CI) of A-RIR preferable/equivalent is greater than 0.45. We also evaluated the NMI improvement from the baseline and the translational/rotational errors between A-RIR and H-RIR. Results The A-RIR preferable/equivalent was selected in twenty-one patients (0.75, 95% CI: 0.55–0.89), demonstrating non- inferiority to H-RIR. The NMI improvement of A-RIR was greater than that of H-RIR in twenty-four patients: the mean value ± SD was 0.225 ± 0.115 in A-RIR and 0.196 ± 0.114 in H-RIR (P <0.001). The absolute translational error was 0.38 ± 0.31 mm. The rotational error was –0.03 ± 0.20, 0.05 ± 0.19, –0.04 ± 0.20 degrees in axial, coronal, and sagittal planes (range: – 0.66–0.52). L. Stolarczyk 1 , J. Folsted Kallehauge 1 , L. Barbosa Valdetaro 1 , L. P. Muren 1 , M. Høyer 1 , P. Randers 2 , T. Stagaard Johansen 1 , H. S. Rønde 1 , M. Sitarz 1 , S. Tilbæk 1 , A. Vestergaard 3 , L. Bentzenb 4 , S. Elleberg Petersena 5 1 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark; 2 Aarhus University Hospital, Danish Center for Particle Therapy, , Aarhus, Denmark; 3 Aarhus University Hospital, Aarhus, Danish Center for Particle Therapy, , Aarhus, Denmark; 4 Aarhus University Hospital, Department of Oncology,, Aarhus , Denmark; 5 Aarhus University Hospital, Aarhus, Denmark, Danish Center for Particle Therapy, Aarhus, Denmark Purpose or Objective Implantation of fiducial markers may potentially expand image-guidance strategies in proton therapy of prostate cancer. However, markers may cause imaging artefacts, and more importantly degradation of the dose distribution of proton beams passing through a high-density marker. As a part of a national randomised trial (PROstate PROTON trial 1) where proton therapy will be delivered concomitantly to the prostate, seminal vesicles and pelvic lymph nodes, we therefore evaluated different commercially available fiducials with respect to their visibility in selected imaging modalities and dose degradation downstream of the markers. Materials and Methods Best Gold Markers (GM) and Gold Anchor (GA) fiducials of different forms and sizes (Table 1) were assessed. Comparison was performed for markers already used in proton RT as well as for a recently developed GA with increased content of iron in the alloy (GA MR+). Markers were implanted in animal tissue positioned inside the Gammex (CIRS) phantom. The phantom underwent CT scanning (Siemens Somatom Definition Edge), magnetic resonance imaging (Philips Ingenia 3T), 2D kV imaging and cone-beam CT scanning (CBCT, ProBeam Varian). Visibility of different markers was assessed qualitatively through visual inspection. The dose distribution downstream of the markers positioned parallel to proton beam was evaluated using EBT3 films (Ashland) in the entrance, in the plateau and at the end of a spread-out Bragg peak (SOBP) with energies ranging from 160 to 190 MeV. Additional dose measurements were obtained with 3D radiochromic dosimeters for the GA-0.4 marker commonly used in proton RT. Conclusion A-RIR shows non-inferior to H-RIR in CT and CT-myelogram registration for postoperative spine SBRT planning. PO-1682 Visibility, artifacts and dose degradations around gold markers in proton therapy of prostate cancer