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Intraoperative MRI-derived volumetric ablation margins and initial correlation with local outcome after MRI-guided
Nienke S de Jager1, Tim J van Oostenbrugge2, Torben Pätz3
1Department of Medical Imaging, Radboud University Medical Center, Geert Grooteplein Zuid 10, P.O. Box 9101, 6525, Nijmegen, GA, Netherlands.
Purpose:
To assess volumetric ablation margins derived from intraoperative pre- and post-ablation MRI after magnetic resonance imaging (MRI)-guided percutaneous cryoablation of renal tumors and explore its correlation with local treatment success.
Methods:
Retrospective analysis was performed on 30 patients (mean age 69y) who underwent percutaneous MRI-guided cryoablation between May 2014 and May 2020 for 32 renal tumors (size: 1.6-5.1 cm). Tumor and ice-ball volumes were segmented on intraprocedural pre- and post-ablation MR images using Software Assistant for Interventional Radiology (SAFIR) software. After MRI-MRI co-registration, the software automatically quantified the minimal treatment margin (MTM),defined as the smallest 3D distance between the tumor and ice-ball surface. Local tumor progression (LTP) after cryoablation was assessed on follow-up imaging.
Results:
Median follow-up was 16 months (range: 1-58). Local control after cryoablation was achieved in 26 cases (81%) while LTP occurred in 6 (19%). The intended MTM of ≥5 mm was achieved in 3/32 (9%) cases. Median MTM was significantly smaller for cases with (- 7 mm; IQR:-10 to - 5) vs. without LTP (3 mm; IQR:2 to 4) (P < .001). All cases of LTP had a negative MTM. All negative treatment margins occurred in tumors > 3 cm.
Conclusions:
Determination of volumetric ablation margins from intraoperative MRI was feasible and may be useful in predicting local outcome after MRI-guided renal cryoablation. In our preliminary data, an intraoperative MRI-derived minimal margin extending at least 1 mm beyond the MRI-visible tumor led to local control and this was more difficult to achieve in tumors > 3 cm. Ultimately, online margin analysis may be a valuable tool to intraoperatively assess therapy success, but larger prospective studies are needed to establish a reliable threshold for clinical use.
Insights
Intraoperative MRI accurately assesses ablation margins for renal cryoablation, predicting local treatment success. Achieving a minimal treatment margin of at least 1mm is crucial for local control, especially in smaller tumors.
Area of Science:
- Interventional Radiology
- Oncology
- Medical Imaging
Background:
- Percutaneous cryoablation is a minimally invasive treatment for renal tumors.
- Accurate assessment of ablation margins is critical for treatment success.
- Intraoperative imaging guidance is essential for precise cryoablation.
Purpose of the Study:
- To evaluate volumetric ablation margins using intraoperative MRI after cryoablation of renal tumors.
- To determine the correlation between these margins and local treatment outcomes.
- To explore the feasibility of real-time margin assessment for predicting cryoablation success.
Main Methods:
- Retrospective analysis of 30 patients with 32 renal tumors treated with MRI-guided cryoablation.
- Segmentation of tumor and ice-ball volumes on pre- and post-ablation MRI.
- Automated quantification of the minimal treatment margin (MTM) using specialized software.
- Assessment of local tumor progression (LTP) on follow-up imaging.
Main Results:
- Local control was achieved in 81% of cases; LTP occurred in 19%.
- The intended MTM of ≥5mm was achieved in only 9% of cases.
- A significantly smaller MTM was observed in cases with LTP (median -7mm) compared to those without (median 3mm).
- All LTP cases had a negative MTM, and all negative margins were in tumors >3cm.
Conclusions:
- Intraoperative MRI-derived volumetric ablation margins are feasible for predicting local outcomes in renal cryoablation.
- A minimal margin of ≥1mm beyond the visible tumor correlated with local control.
- Achieving adequate margins was more challenging for tumors larger than 3cm.
- Online margin analysis may enhance intraoperative assessment of cryoablation success, warranting larger prospective studies.
