ESTRO 2023 - Abstract Book

S404

Sunday 14 May 2023

ESTRO 2023

PD-0496 Feasibility of MR-only Interstitial HDR Brachytherapy with ZTE Imaging for Catheter reconstruction H. Alsaleh 1 , S. Aldelaijan 2 , B. Moftah 2 1 king Faisal Specialist Hospital & Research Centre, Biomedical Physics, Riyadh , Saudi Arabia; 2 king Faisal Specialist Hospital & Research Centre, Biomedical Physics , Riyadh , Saudi Arabia Purpose or Objective One of the main challenges for MR-only interstitial brachytherapy treatment planning is that the implanted plastic needles cannot be detected with acceptable accuracy using conventional MR T1 and T2 weighted images. Since thin plastic needles are not visible in CT scans, the current workflow requires the acquisition of CT images with marker-filled catheters for registration with MR images and needle reconstruction. Eventual changes between MR and CT scans could lead to registration errors and affect the calculated dose. In this work, we aim to evaluate the feasibility of MR-only workflow using ZTE images with conventionally used CT markers for the detection and reconstruction of interstitial needles as an alternative to the CT approach. Materials and Methods Two ProGuide interstitial plastic needles (one rounded and one sharp) 6Fx294mm (Elekta, Stockholm, Sweden) were inserted into a melon and scanned with and without CT-marker in a Signa Premier 3T MRI system (GE Healthcare) and a Brilliance big-bore CT (Philips, Netherland). The phantom was CT-scanned and subsequently, coronal 3D MR images were acquired with MPRAGE T1W (TR/TE 2308/4 ms, FOV 200, matrix 288), CUBE T2W (TR/TE 3000/108 ms, FOV 200, matrix 288) and ZTE (TR/TE 647/0.016, FOV 200, matrix 288). Scan time was approximately identical for all MR sequences. MR images were registered to CT images for comparison. Registered CT and MR images were sent to the Oncentra treatment planning system (Nucletron B.V, Netherlands) for manual catheter reconstruction and determination of the first dwell position. Results Susceptibility-induced artifacts around the empty needles are pronounced in T1w and T2w images as shown in the first row of figure 1 (green arrows). ZTE image with CT-like contrast showed a clear depiction of the empty catheters with no distortion. With CT marker, distortion increased around the needles in T1w and T2w images (red arrows) while ZTE images present less artifact and a uniform signal void around the marker. Furthermore, the metal-induced susceptibility artifact in the ZTE image (blue arrows) correlates well with the bright part of the marker in the CT image. Catheter reconstruction with Oncentra TPS on the reference CT image demonstrated a very good positional agreement of the first dwell position between CT and registered ZTE image as compared to conventional T1w and T2w images.

Conclusion In this work, we demonstrated that MR-only interstitial gynecologic HDR brachytherapy workflow is feasible with Zero TE MR sequence with CT marker for needle reconstruction as an alternative for CT scanning. ZTE images showed CT-like contrast and minimal metal-induced susceptibility artifact around the needles. Future clinical investigation is required to confirm these initial results for clinical workflow. PD-0497 Initial results for a state of the art “transferless” multi-modality imaging brachytherapy suite F. Lacroix 1 , N. Dufour 2 , M. Lefebvre 2 , S. Aubin 2 , M. Lavallee 2 , J. Morrier 2 , E. Vigneault 2 , M. Froment 2 , W. Foster 2 , L. Beaulieu 2 , E. Poulin 2 1 CHU de Quebec-Universite Laval, Radio-oncologie, Quebec, Canada; 2 CHU de Quebec, Radio-oncologie, Quebec, Canada Purpose or Objective This work focusses on CHU de Québec-Université Laval’s initial 6 months experience in a new state of the art brachytherapy suite optimized for gynecology patients housing an OR, a dedicated MR and a sliding gantry CT. A Kevlar CT and MR compatible tabletop is used to move the patient from the OR to the MR to the CT, making the procedure “transferless” (i.e. patient remains on the same surface). Initial results are presented and compared to a standard multiple manual transfer procedure to validate if this concept minimizes the patient’s applicator/needle displacements.

Materials and Methods