Tumor and Ablation Margin Visibility during Cryoablation of Musculoskeletal Tumors: Comparing Intraprocedural PET/CT Images with CT-Only Images

Abstract

Purpose: To compare tumor and ice-ball margin visibility on intraprocedural positron emission tomography (PET)/computed tomography (CT) and CT-only images and report technical success, local tumor progression, and adverse event rates for PET/CT-guided cryoablation procedures for musculoskeletal tumors.

Materials and methods: This Health Insurance Portability and Accountability Act (HIPAA)-compliant and institutional review board-approved retrospective study evaluated 20 PET/CT-guided cryoablation procedures performed with palliative and/or curative intent to treat 15 musculoskeletal tumors in 15 patients from 2012 to 2021. Cryoablation was performed using general anesthesia and PET/CT guidance. Procedural images were reviewed to determine the following: (a) whether the tumor borders could be fully assessed on PET/CT or CT-only images; and (b) whether tumor ice-ball margins could be fully assessed on PET/CT or CT-only images. The ability to visualize tumor borders and ice-ball margins on PET/CT images was compared with that on CT-only images.

Results: Tumor borders were fully assessable for 100% (20 of 20; 95% CI, 0.83-1) of procedures on PET/CT versus 20% (4 of 20; 95 CI, 0.057-0.44) of procedures on CT only (P < .001). The tumor ice-ball margin was fully assessable in 80% (16 of 20; 95% CI, 0.56-0.94) of procedures using PET/CT versus 5% (1 of 20; 95% CI, 0.0013-0.25) of procedures using CT only (P < .001). Primary technical success was achieved in 75% (15 of 20; 95% CI, 0.51-0.91) of procedures. There was local tumor progression in 23% (3/13; 95% CI, 0.050-0.54) of the treated tumors with at least 6 months of follow-up. There were 3 adverse events (1 Grade 3, 1 Grade 2, and 1 Grade 1).

Conclusions: PET/CT-guided cryoablation of musculoskeletal tumors can provide superior intraprocedural visualization of the tumor and ice-ball margins compared with that provided by CT alone. Further studies are warranted to confirm the long-term efficacy and safety of this approach.

Figure 1.

Derivation of positron emission tomography (PET)/ computed tomography (CT)–guided musculoskeletal (MSK) tumor cryoablation procedures performed from 2012 to 2021. MR = magnetic resonance.

Figure 2.

Comparison of computed tomography (CT)–only images with positron emission tomography (PET) and fused PET/CT images to compare tumor visibility. Case 1: ovarian cancer metastasis in the rectus muscle (arrows)—the medial margin was obscured by the adjacent rectus muscle (asterisks) on CT but well delineated on PET/CT. Case 2: lung cancer metastasis in the sacrum (white arrows)—margins were underestimated by the lytic lesion on CT but were better seen to extend medially and posteriorly (asterisks) on the PET/CT. Case 3: bladder cancer metastasis in the left iliac bone (arrows)—the lesion demonstrated a mixed lytic and sclerotic appearance on CT, but PET/CT confirmed only the lytic component to be metabolically active tumor. The sclerotic portion (asterisks) was not metabolically active.

Figure 3.

Comparison of intraprocedural computed tomography (CT)–only images with positron emission tomography (PET)/ CT images during cryoablation. Case 1: testicular cancer metastasis in the right paraspinal region—CT-only images demonstrated the ice ball (arrows), but the tumor was not seen. On the fused PET/CT image, the tumor (asterisk) was well seen and the ice-ball margin was assessable circumferentially by examining how far the ice ball (arrows) extended beyond the tumor. Case 2: renal cell cancer metastasis in the scapula—the CT-only image showed the ice ball (arrows); however, the isodense metastasis was obscured within the ice ball. The PET/CT image showed the tumor (asterisk) engulfed by the ice ball (arrows). Again, the ablation margin could be inferred by how far the ice extended beyond the tumor over the entire tumor circumference.