The data used in this study were extracted from the ‘Minimally Invasive Thermal Ablation (MISTRAL) study’ database, a registry of all thermal ablation procedures performed at the University Medical Center Utrecht (Utrecht, The Netherlands). Permission was granted by the local institutional review board (No. 21/709), and the requirement for informed consent was waived.

All consecutive patients with intraparenchymal or US-occult renal tumors scheduled for ablation using the RenACAGA technique between January 1, 2022, and July 1, 2024, were included in this retrospective analysis. Any histological subtype was included. All patients were referred for thermal ablation through a multidisciplinary tumor board.

A flowchart outlining the procedural steps involved in the RenACAGA technique is presented in Fig. 1.

A flowchart of procedural steps involved in the RenACAGA technique. First, the femoral or radial artery was punctured, and a catheter was advanced to the renal artery. A C-arm CT with intra-arterial contrast was then performed to identify the target lesion and plan the needle trajectory by selecting the skin entry point and target. Next, the needle was advanced along the planned trajectory, followed by a C-arm CT scan to confirm accurate positioning. Once confirmed, ablation was initiated. Immediately after ablation, a C-arm CT scan was performed and fused with the pre-ablation scan to assess ablation margins. If the margins were inadequate, additional ablation was performed. Intra-arterial contrast was administered during all C-arm CT scans

Treatment was performed in an angiography suite under general anesthesia to enable apnea during C-arm CT and needle placement. C-arm CT was performed using a monoplane C-arm system (Allura FD20 Xper, Philips, Best, the Netherlands) in propeller position with an ‘open trajectory rotation’ (240° rotation, 308 projections) and 10.4 s rotation time (XperCT HD fast setting). Positioning (prone or supine) depended on tumor location.

Prone position: Arms placed alongside the body, palms up, allowing simultaneous radial artery and flank access for needle placement (Fig. 2).

A Schematic representation of the catheterization of the right renal artery for intra-arterial contrast injection (10–30 ml) via radial access; B Patient positioning—The patient is in prone position with arms next to the body. Radial artery access site (black arrow), exposed flank to puncture the left kidney (white arrow); C Radial artery puncture site (black arrow) with a guidewire in position

Supine Position: The femoral artery was used for access, with one arm raised above the head for flank access.

Radial or femoral arterial access was achieved under ultrasound guidance. For radial access, a 5F sheath (Glidesheath™, Terumo) was inserted, followed by a 5F catheter (Performa, Merit) into the appropriate renal artery. For femoral access, a 6F sheath (Radifocus™, Terumo) was placed, followed by a 5F cobra catheter (Glidecath™, Terumo). Selective microcatheters (Progreat™, Terumo) were used in certain cases to access more specific branches of the renal artery.

C-arm CT was performed during apnea and synchronized with intra-arterial contrast injection (renal arteriography) (Fig. 3). A 2:1 mixture of contrast agent (Visipaque 320 mg/ml) and saline was injected at a rate of 1.0–1.5 ml/s, with a 10-s scan delay. 10–30 ml of diluted contrast agent was used per C-arm CT.

Example of RenACAGA ablation of a tumor in the upper pole of the left kidney. A Digital subtraction angiography of the left renal artery shows the target lesion (white arrow); B The target lesion (white circle) visualized with C-arm CT renal arteriography (C-arm CTRA); C Ablation needle in position; D and E Pre- and post-ablation C-arm CTRAs are fused with XperGuide software (Philips) in axial and coronal planes, showing adequate ablation margins

C-arm CT images were utilized to identify the target lesion and plan the trajectory for the microwave antenna (Emprint, Medtronic) or RFA applicator (Cooltip, Medtronic). Needle trajectory was planned using C-arm navigation software (XperGuide, Philips), which facilitated selection of the skin entry point and target lesion (Fig. 4). Using fluoroscopy, the needle was inserted along the projected path, and a confirmatory C-arm CT was obtained. If the needle position was incorrect, adjustments were made.

Example of navigation with XperGuide software (Philips). A Coronal view of the target lesion (largest diameter: 30 mm); B Entry point view, showing the entry point (pink circle) and target (green circle) projected on top of each other. The needle tip is aimed perpendicularly at the center of the planned needle trajectory. Next, the ablation needle is rotated 90 degrees to align directly with the projected needle trajectory (needle tip is kept at same position) to advance the needle in a straight line from entry point to target; C Perpendicular view to assess needle depth; D Needle is placed in center of target lesion

Once the needle was connected to the generator (Emprint HP or Cooltip, Medtronic), ablation was initiated. Post-ablation C-arm CT with renal arteriography was performed to assess the ablation zone and identify potential complications. Pre- and post-ablation C-arm CTs were fused (XperGuide, Philips) to assess ablation margins (Fig. 3). In case of a minimum ablation margin < 5 mm, additional ablation was performed with needle repositioning if necessary. After ablation, the needle was withdrawn under tract ablation, and the catheter and sheath were removed. Hemostasis was achieved by applying compression at the arterial access site using an inflatable wristband (Safeguard Radial™, MeritMedical) for 2 h or with a vascular closure device (Angio-Seal™, Terumo) for the groin.

Technical success: Technical success was defined as the successful completion of the ablation procedure according to the RenACAGA technique, without switching to alternative modalities like US or conventional CT.

Complications: Adverse events occurring during or within 30 days post-procedure were documented by reviewing patient records. Complications were classified according to the Common terminology criteria for adverse events (CTCAE) v5.0 [13].

Procedure duration: Data on procedure duration were obtained from anesthesiology reports. "In-room time" was the time between patient entry and exit from the angiography suite, while "procedure time" was the time from arterial puncture to access site compression.

Radiation dose: The radiation dose received by the patient was measured as total dose–area product (DAP, Gy·cm2). To determine the effective dose (mSv), the total DAP was multiplied by a system-specific conversion factor of 0.38 mSv/Gy·cm2 [14].

Local Tumor Recurrence (LTR): MRI or CT performed at 1, 3, and 6 months, and every 3–6 months thereafter, were reviewed to assess LTR. Any possible or definitive residual or local recurrence of the tumor at the site of the ablation zone was considered as LTR.