Impact of 90Y PET gradient-based tumor segmentation on voxel-level dosimetry in liver radioembolization

• Published in: EJNMMI physics Vol. 5; no. 1; pp. 1 - 17
• Main Authors: Mikell, Justin K., Kaza, Ravi K., Roberson, Peter L., Younge, Kelly C., Srinivasa, Ravi N., Majdalany, Bill S., Cuneo, Kyle C., Owen, Dawn, Devasia, Theresa, Schipper, Matthew J., Dewaraja, Yuni K.
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 30-11-2018; Springer Nature B.V; SpringerOpen
• Subjects: 90Y; 90Y PET; Applied and Technical Physics; Auto-segmentation; Biological effects; Computational Mathematics and Numerical Analysis; Computed tomography; Correlation coefficients; Diagnostic systems; Dosimeters; Dosimetry; Engineering; Histograms; Image segmentation; Imaging; Imaging and dosimetry for radionuclide based therapy; Lesions; Liver; Medicine; Medicine & Public Health; Methods; Nuclear Medicine; Original Research; Patients; Radioembolization; Radiology; Tumor segmentation; Tumors; Yttrium isotopes; Auto-segmentation; Y; Dosimetry; Radioembolization; Tumor segmentation; Y PET; Gradient-based segmentation
• ISSN: 2197-7364; 2197-7364
• DOI: 10.1186/s40658-018-0230-y

Background
The purpose was to validate
90
Y PET gradient-based tumor segmentation in phantoms and to evaluate the impact of the segmentation method on reported tumor absorbed dose (AD) and biological effective dose (BED) in
90
Y microsphere radioembolization (RE) patients. A semi-automated gradient-based method was applied to phantoms and patient tumors on the
90
Y PET with the initial bounding volume for gradient detection determined from a registered diagnostic CT or MR; this PET-based segmentation (PS) was compared with radiologist-defined morphologic segmentation (MS) on CT or MRI. AD and BED volume histogram metrics (D90, D70, mean) were calculated using both segmentations and concordance/correlations were investigated. Spatial concordance was assessed using Dice similarity coefficient (DSC) and mean distance to agreement (MDA). PS was repeated to assess intra-observer variability.
Results
In phantoms, PS demonstrated high accuracy in lesion volumes (within 15%), AD metrics (within 11%), high spatial concordance relative to morphologic segmentation (DSC > 0.86 and MDA < 1.5 mm), and low intra-observer variability (DSC > 0.99, MDA < 0.2 mm, AD/BED metrics within 2%). For patients (58 lesions), spatial concordance between PS and MS was degraded compared to in-phantom (average DSC = 0.54, average MDA = 4.8 mm); the average mean tumor AD was 226 ± 153 and 197 ± 138 Gy, respectively for PS and MS. For patient AD metrics, the best Pearson correlation (
r
) and concordance correlation coefficient (ccc) between segmentation methods was found for mean AD (
r
 = 0.94, ccc = 0.92), but worsened as the metric approached the minimum dose (for D90,
r
 = 0.77, ccc = 0.69); BED metrics exhibited a similar trend. Patient PS showed low intra-observer variability (average DSC = 0.81, average MDA = 2.2 mm, average AD/BED metrics within 3.0%).
Conclusions
90
Y PET gradient-based segmentation led to accurate/robust results in phantoms, and showed high concordance with MS for reporting mean tumor AD/BED in patients. However, tumor coverage metrics such as D90 exhibited worse concordance between segmentation methods, highlighting the need to standardize segmentation methods when reporting AD/BED metrics from post-therapy
90
Y PET. Estimated differences in reported AD/BED metrics due to segmentation method will be useful for interpreting RE dosimetry results in the literature including tumor response data.