Conventional 3D staging PET/CT in CT simulation for lung cancer: impact of rigid and deformable target volume alignments for radiotherapy treatment planning

Abstract

Objective: Positron emission tomography (PET)/CT scans can improve target definition in radiotherapy for non-small cell lung cancer (NSCLC). As staging PET/CT scans are increasingly available, we evaluated different methods for co-registration of staging PET/CT data to radiotherapy simulation (RTP) scans. Methods: 10 patients underwent staging PET/CT followed by RTP PET/CT. On both scans, gross tumour volumes (GTVs) were delineated using CT (GTV CT ) and PET display settings. Four PET-based contours (manual delineation, two threshold methods and a source-to-background ratio method) were delineated. The CT component of the staging scan was co-registered using both rigid and deformable techniques to the CT component of RTP PET/CT. Subsequently rigid registration and deformation warps were used to transfer PET and CT contours from the staging scan to the RTP scan. Dice's similarity coefficient (DSC) was used to assess the registration accuracy of staging-based GTVs following both registration methods with the GTVs delineated on the RTP PET/CT scan. Results: When the GTV CT delineated on the staging scan after both rigid registration and deformation was compared with the GTV CT on the RTP scan, a significant improvement in overlap (registration) using deformation was observed (mean DSC 0.66 for rigid registration and 0.82 for deformable registration, p50.008). A similar comparison for PET contours revealed no significant improvement in overlap with the use of deformable registration. Conclusions: No consistent improvements in similarity measures were observed when deformable registration was used for transferring PET-based contours from a staging PET/CT. This suggests that currently the use of rigid registration remains the most appropriate method for RTP in NSCLC.

Comparative evaluation of target volumes defined by deformable and rigid registration of diagnostic PET/CT to planning CT in primary esophageal cancer

“…Moreover, it also suggests that caution should be exercised when applying DIR for propagating gross target volumes between diagnostic PET/CT and planning CT for EC because of the inconsistent results. Our results were comparable to a previous investigation by Hanna et al [17] They compared the DSC and the displacements of COM between staging PET/CT rigid registered and deformable registered with RTP PET/CT scan for 10 lung cancer patients. The improvements were only observed for CT-to-CT-based contours with deformable registration.…”

Impact of FDG‐PET on lung cancer delineation for radiotherapy

“…In addition, we assessed the impact of PET/CT data on trainees and qualified ROs separately and found a difference. Superior methods of motion management 20 and deformable co‐registration 21 may have a greater impact upon variability in contouring than the use of dedicated planning PET. However, not all centres have access to these technologies and so the techniques using PET/CT, whilst not aimed primarily at motion management, may have some utility for this purpose.…”

Dose–function Histogram Evaluation Using 99mTc-GSA SPECT/CT Images for Stereotactic Body Radiation Therapy Planning for Hepatocellular Carcinoma Patients: A Dosimetric Parameter Comparison

“…After registration between SPECT and CT images by hardware arrangement, we registered SPECT/CT images onto the planning CT images: a rigid image registration followed by a non-rigid deformable registration. During this process, each SPECT voxel was mapped to a new position based on the transformations used in the CT-CT registration, resulting in new SPECT/CT fused images that were deformably registered with the planning CT images (12). Structures of the irradiated volumes of the liver parenchyma were generated at 5-Gy dose increments, based on the dose distribution information.…”