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. 2024 Feb 29;15(1):356-367.
doi: 10.21037/jgo-23-890. Epub 2024 Feb 26.

Prospective comparison of positron emission tomography (PET)/magnetic resonance and PET/computed tomography dosimetry in hepatic malignant neoplastic disease after 90Y radioembolization treatment

Ram Gurajala  1 , Sasan Partovi  1 , Frank P DiFilippo  2 , Xin Li  3 , Christopher Coppa  4 , Shetal N Shah  2   4 , Karunakaravel Karuppasamy  1 , Nancy Obuchowski  5 , Ehsan Fayazzadeh  6 , Gordon McLennan  7 , Abraham Levitin  1
Affiliations

Prospective comparison of positron emission tomography (PET)/magnetic resonance and PET/computed tomography dosimetry in hepatic malignant neoplastic disease after 90Y radioembolization treatment

Ram Gurajala et al. J Gastrointest Oncol. .

Abstract

Background: 90Y radioembolization is an established treatment modality for hepatic malignancies. Successful radioembolization requires optimal dose delivery to tumors while minimizing dosages to parenchyma. Post-treatment positron emission tomography (PET)/computed tomography (CT) dosimetry is the established benchmark, whereas PET/magnetic resonance (MR) is an emerging modality. The goal of this study was to assess the intermodality agreement between PET/MR and PET/CT 90Y dosimetry.

Methods: In this single-institution study, 18 patients (20 treatment sessions) with a primary or metastatic hepatic malignancy underwent both PET/MR and PET/CT after 90Y radioembolization. Patients were randomized to undergo one modality first, followed by the other. The region of interest was delineated using MR images and tumor and liver dosimetry was calculated. Intermodality agreement was assessed using the Bland-Altman method. A generalized linear model was used to assess the effect of baseline variables on intermodality dose differences.

Results: PET/MR underestimated tumor and liver absorbed doses when compared to PET/CT by -3.7% (P=0.042) and -5.8% (P=0.029), respectively. A coverage probability plot demonstrated that 80% and 90% of tumor dose measurements fell within intermodality differences of 11% and 18%, respectively. PET/MR underestimated tumor dose at both low (<1 GBq) and high (>3 GBq) injected activity levels (P<0.001) by -22.3 [standard deviation (SD) =13.5] and -24.3 (SD =18.7), respectively.

Conclusions: Although PET/MR significantly underestimated the absorbed dose when compared to PET/CT, the intermodality agreement was high and the degree of underestimation was better than previously reported. Intermodality differences were more pronounced at low and high injected doses. Additional studies are required to assess the clinical implications of these findings.

Keywords: 90Y dosimetry; PET/computed tomography (PET/CT); Positron emission tomography (PET)/magnetic resonance (MR); hepatic malignancy; radioembolization.

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Conflict of interest statement

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jgo.amegroups.com/article/view/10.21037/jgo-23-890/coif). All authors report that this study was partially funded by a research grant from Cleveland Clinic Foundation Imaging Institute and by a research grant from Siemens Medical Solutions, USA. The authors have no other conflicts of interest to declare.

Figures

Figure 1
Figure 1
An example of treated tumor with radioembolization and subsequent PET/CT and PET/MR images. (A) Intraprocedural cone-beam CT image demonstrating a hypervascular segment VIII lesion. (B) Post-90Y radioembolization PET/CT image cannot definitively confirm adequate tumor coverage. (C) Post-90Y radioembolization PET/MR clearly demonstrates nontarget uptake medially and inadequate coverage of the lesion posterolaterally (star). PET, positron emission tomography; CT, computed tomography; MR, magnetic resonance.
Figure 2
Figure 2
An example of treated tumor with radioembolization and subsequent PET/CT and PET/MR images. Noncontrast CT (A) and MR (B) images obtained after 90Y radioembolization. Attenuation-corrected PET images derived from PET/CT (time-of-flight technique) (C) and derived from PET/MR (T1-weighted Dixon sequences leading to a 4-class segmentation model) (D). Fused PET/CT (E) and PET/MR (F) images with contours drawn around the liver (orange), tumor (blue), and lobe separation (white). PET, positron emission tomography; CT, computed tomography; MR, magnetic resonance.
Figure 3
Figure 3
An example of treated tumor with radioembolization and subsequent PET/CT and PET/MR images. (A) Patient with prior partial right liver lobe resection who presented for 90Y radioembolization of recurrent lesions in segments IVa and II (thin blue arrows). (B) Post-90Y radioembolization PET/CT dosimetry suggested inadequate coverage of the segment IVa lesion and no coverage of the segment II lesion. Blue outline defined the boundary of the tumor. Based on these results, the decision was made to pursue a second 90Y radioembolization treatment session. (C,D) Post-90Y radioembolization PET/MR images obtained after the second treatment session clearly demonstrated an interval growth of the segment II lesion with suboptimal radiotracer coverage (thick blue arrows), as well as adequate treatment coverage of the segment IVa lesion based on the visual appearance and dosimetry calculations. As a result, the patient was referred for external beam radiation of the growing segment II lesion. There would have likely been a delay in treatment of this lesion had PET/MR not been performed. PET, positron emission tomography; CT, computed tomography; MR, magnetic resonance.
Figure 4
Figure 4
Various plots of intermodality differences at varying administered dose levels. (A) The diffliver was plotted against the meanliver. There was significant underestimation of liver dose with PET/MR but no significant trend between the underestimation and the magnitude of the liver dose (P=0.338). The mean underestimation was −3.1 (SD =5.9), with 95% CI of –5.8 to –0.35. (B) The difftumor was plotted against the meantumor. There was significant underestimation of tumor dose with PET/MR but no significant trend between the underestimation and the magnitude of the tumor dose (P=0.502). The mean underestimation was −9.4 (SD =24.1), with 95% CI of −18.8 to −0.34. PET, positron emission tomography; MR, magnetic resonance; SD, standard deviation; CI, confidence interval.
Figure 5
Figure 5
The degree of intermodality agreement was plotted against the degree of intermodality differences as a percentage of positron emission tomography/computed tomography value. At a difference of <18%, more than 90% intermodality agreement was achieved. MR, magnetic resonance; CT, computed tomography.
Figure 6
Figure 6
Intermodality differences in tumor dose measurements were plotted against the injected activity levels. There was significant underestimation of tumor dose with positron emission tomography/magnetic resonance at both low (<1 GBq) and high (>3 GBq) levels and little bias between 2 and 3 GBq (P<0.001 for nonlinear relationship), suggesting that the magnitude of underestimation depends on the injected activity level. difftumor, intermodality difference in tumor dose.
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