MPP07  Presentation Time: 4:54 PM: Clinical Implementation of Optimized Magnetic Resonance Sequences in the Treatment Planning of Surface Brachytherapy

• Published in: Brachytherapy Vol. 24; no. 4; pp. S18 - S19
• Main Authors: Lavelle, Michael, Devlin, Phillip, Kaza, Evangelia, Buzurovic, Ivan
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.07.2025
• ISSN: 1538-4721
• DOI: 10.1016/j.brachy.2025.06.029

The clinical standard practice of surface brachytherapy (SBT) planning has long been to use computed tomography (CT) imaging to visualize applicators for catheter reconstruction in the treatment planning process. Recent work in SBT has suggested that magnetic resonance (MR)-guidance can be used in place of CT-guidance in SBT planning to utilize the increased soft tissue contrast for visualization of diseased tissue. This soft tissue visualization can be used to verify the target depth for enhanced coverage of the clinical target volume. Two optimized MR sequences (pointwise encoded time reduction with radial acquisition and volumetric interpolated breath-hold examination (VIBE)) have been shown to detect sufficient signal from the silicon-based applicators to perform accurate catheter reconstruction. The VIBE Dixon opposed-phase (DOP) series display superior soft tissue contrast and therefore is considered most-suited for SBT planning. The purpose of this study is to demonstrate that MR-guided SBT planning using the DOP series can produce clinical plans comparable to CT-guided plans through segmentation of volumetric isodose clouds and point-based dose difference calculations. The hand and foot of an anthropomorphic phantom (True Phantom Solutions, Ontario, Canada) and the hands of five patients undergoing SBT treatment for Dupuytren’s Contracture/Palmar fascial fibromatosis were fitted with flap-style (Elekta, Netherlands) applicators and imaged with a VIBE sequence to obtain DOP images. Helical CT scans for all subjects were acquired for the creation of verification plans. SBT planning was performed in Oncentra Brachy (Elekta Brachytherapy, The Netherlands) treatment planning software in parallel for both the CT-based and MR-based image sets. The MR-based plan was rigidly registered to the CT-based plans, and the isodose volumes were segmented to V150, V125, V100, V95, V90, V80, and V65 and compared using the Dice similarity coefficient (DSC). Additionally, dose points were chosen throughout the volume and on the surface to perform dose difference calculations for treatment plan comparisons. The Cartesian coordinates of these dose points were transformed from the MR-based plans to the CT-based plans using the transformation matrix from a rigid registration, and the doses of the corresponding points were compared using a dose difference calculation. The DOP series demonstrated excellent visibility of both the flap applicators and diseased tissue. The DSC’s for the isodose volumes V150, V125, V100, V95, V90, V80, and V65 were on average 0.85, 0.91, 0.93, 0.96, 0.97. 0.97, and 0.98 for the phantom and 0.75, 0.90, 0.91, 0.93, 0.94. 0.94, and 0.95 for the patients, respectively. There is a relatively low overlap for V150; however, this result is not a concern as this isodose volume has no clinical relevance. The dose difference calculations were on average 1.42% for the phantom and 3.79% for the patients. The higher dose difference calculation and lower overlap for the patients can be attributed to motion between scans. The figure contains the DOP image (top left), the catheter reconstruction (top center), the isodose lines of the CT-MR fusion for patient 5 (top right), average dose differences across all subjects (bottom left), DSC’s for patient 5 (bottom center), and the phantom foot (bottom right). The high overlap of the DSC’s (>0.90) for all clinically relevant dose volumes and the low dose differences for the point-based calculations (< 5%) imply that DOP is well suited for SBT planning. By implementing the DOP series in the SBT planning process, patient-specific data can be considered in the treatment planning process ensuring proper coverage of the clinical target, which can potentially reduce the need of retreatment due to insufficient coverage of the target volume.