Thermal ablation of the most challenging cases of liver metastases

Abstract

Patient selection for image-guided thermal ablation of liver metastases has to be taken in a multidisciplinary tumor board given the extreme complexity of cancer metastatic disease, and the numerous treatment options offered to oligometastatic patient today.

The role of image-guided thermal ablation increases over years in the treatment of liver metastases. In order to fulfill the expected outcomes which are to have a local control rate equivalent to surgery, interventional oncologist have to take every measure that will help when treating most challenging metastases including image guidance, anesthesia, respiration monitoring, ablation technique, confirmation software that can favor positive outcomes, and in some way to render challenging metastases easy to treat.

Cancer treatment is challenging in most patients, and even more when it deals with metastatic cancer where the balance in between systemic therapy and local treatment may vary from one patient to another but even more surprisingly, indication for and type if local treatment may varies from center to another. Oligometastatic patient traditionally defines as patient with one to five metastatic lesions, predominantly visceral with controlled or resected primary tumor (optionally resected). Such definition might change in the near future considering molecular subtypes with specific prognostic in he quest to identify the oligometastatic patient that can benefit from local treatment which is still ongoing and we are missing strong predictive factors to clearly determined if the patient will remain oligometastatic or will become a diffuse disease at a later time point. Indeed, beside the well organize guidelines that set the frame, where today thermal ablation of liver metastases is for non-surgical candidate, a lot of thermal ablations are decided at the tumor board where every patient has his specificities, past history and comorbidities as well as his own cancer history. As recommended by many cancer scientific societies and cancer guidelines only tumor board including medical oncologist, surgeon, diagnostic radiologist, intervetionnal radiologist, radiation therapist and pathologist can solve the complexity described above. One of our challenge of today is that we lack predictive factor for both local success (beside tumor size and vessels proximity), and overall survival (beside long disease-free interval and tumor load) in order to best select oligometastatic patients. Additional randomized control trials on liver metastases are paucity, and some of them like the CLOCC trials ¹ are not translated into guidelines. And even if local tumor control of thermal ablation and surgery are comparable, ² there is still debate for ablation as first-line therapy in small size colorectal cancer metastasis.

Besides every indication that need to be discussed at tumor board and discuss according to benefit balance of other option, there are of course technical challenges for optimal thermal ablation aiming at high rate of local tumor control including, location, visibility during the ablation procedure, proximity of large vessels, bile ducts or extrahepatic vulnerable structures such as digestive tract, and of course tumor size. Most of us will agree that thermal ablation is a curative treatment, and as such we should maximize our local control rate and render the treatment as low challenging as possible. Consequently, selection of metastases 3 cm in diameter or smaller is wise. ² To render challenging case as low challenging as possible, setting the condition to optimize outcomes include:

• Access to general anesthesia that will improve patient and treating physician comfort with no “pain pressure” or “time pressure”. ³ Moreover, it allows respiratory control that might favor accurate targeting. And jet-ventilation must probably be available in our practice. In our center, not a patient who can benefit general anesthesia is treated under sedation, and jet ventilation is the by default technique and is always available with anesthesiologist trained to this technique, because it decreases tumor mobility. ⁴

• Access to as many as possible image guidance technique that will improve any tumor visibility issues. Ultrasound is a no brainer, but CT must be available and will allow puncture in any angulation as you will have the large bore high Z-axis coverage with numerous detectors number CT. I mean a CT with a large covering in the Z-Axis. We do not need second-hand CT from diagnostic department, we need CT for intervention: wide bore, large covering and speed of acquisition/reconsruction, with specific “puncture” software and display. CT+angiography in the same room is a need. With a catheter in the hepatic artery, CT will provide impressive visualization and will allow for repeated imaging during targeting but also for ablation margin monitoring, because with 10 cc of contrast or less in the hepatic artery you will have better visibility of the target than with 90 cc i.v. and as a cherry on top you can repeat it as much as needed because of low renal toxicity. Of course, Lipiodol tagging must be part of your possibilities. MRI and PET guidance might be envisioned but usually difficult to have. Our ceter has been user of an angio-CT room for then past 14 years and it is obvious that any complex ablation is performed in this room and placing the tips of a 5French catheter in the hepatic artery is integral part of the treatment.

• Access to robotic, even if still in its infancy, might help for tumor that can be seen only once before they disappear after i.v. injection. It can help for very steep angle in the Z axis and no doubt they will be the standard of care for multiple needle insertion such cryoablation or IRE, or even multiple antennas RFA as already demonstrated by some pioneers. The group from Reto Bale has clearly demonstrated what can be achieved with a robot when doing stereotactic RFA and there is more to come with simple or sophisticated robotic navigation tools. ⁵ We demonstrated recently how accurate can be the robot in an animal setting an moreover how it flatten the learning curve, ^6,7 and will be probably even more helpful for multiple needle treatment such cryoablation and irreversible electroporation where parallelism and spacing of needles is key.

• Access to multiple ablation technology including microwave ablation (MWA), radiofrequency ablation (RFA) with possibility of non-thermal ablation, as well as perform vascular occlusion, and be able to discuss surgery is needed especially for tumor close to large vessels.

• Access to confirmation software to evaluate ablation margins at time of ablation can greatly help for complex tumor, and even for all tumors treated, ⁸ as the impact of large enough ablation margins on local tumor control has been emphasis in many publications, ⁹ with 5 mm being the minimal to expect and 10 mm being optimal.

Some argue that availability of sophisticated image guidance when needed, robotic, multiple options in the ablation technology, possibility to temporary occlude a vein, ⁹ aero or thermo dissection, general anesthesia, jet ventilation are too much complexity and will transform a simple procedure in a complex treatment. I will argue that a complete ablation is our priceless common goal and all the effort must be done to reach this goal for sake of the patient but also of credibility. Any interventional oncologist remembering his last consultation when a local recurrence was depicted will agree about the need for access when needed to more sophistication in ablation, way beyond a simple ultrasound-guided puncture under conscious sedation.

When developing your ablation practice for liver metastases, we will face “easy” and “challenging” metastases to treat. We have to be ready for the challenging ones to the point they will become easy one. Of course, beyond ablation guidance, technology, monitoring interventional oncologist must be aware of combination treatment ¹⁰ with immune checkpoint inhibitors or maybe immunoablation ¹¹ by direct intratumoral injection¹² of immunomodulators, that will for sure play a role in the future.