Ablation offers options for unresectable tumors

"What drugs will not cure, the knife will; what the knife will not cure, the cautery will; what the cautery will not cure must be considered incurable."-Hippocrates

Imagine destroying a tumor in six minutes with a small needle electrode placed through the skin into a tumor deep in the human body, so that the patient is cured after spending only a few hours in the hospital and leaves with just a small bandage. This may sound like science fiction, but it is reality in many medical centers around the world.

It seems like yesterday that I was a resident rotating through Massachusetts General Hospital, helping Dan Rosenthal treat an osteoid osteoma by radiofrequency ablation. That defining event, which took place 14 years ago, was my first exposure to image-guided tumor ablation, and that seminal work¹ encouraged me and others to become involved in this burgeoning field of medicine. As guest editor of this issue devoted to image-guided ablation, I would like not only to share my thoughts on the past and present, but also to shed some light on patient management and follow-up. I thank my fellow contributors to this supplement for their concise and clinically relevant overviews of the most important areas of image-guided tumor ablation. I found them balanced and extremely well written.

Over the past decade, we have seen a continued expansion of clinical applications for ablative techniques through single-center trials and several multicenter trials designed to rigorously document safety and efficacy. The proliferation of ablation technology and its dissemination into the treatment of various solid tumors is the reason for this update, which will be invaluable for those interested in introducing this new technology in their radiology practices as well as those who are already using it. The short reviews highlight the current knowledge of image-guided tumor ablation in liver, kidney, bone, and lung and illustrate its use with pertinent clinical examples. We understand that some areas of utilization are further along in widespread implementation than others, and for those areas that are less well researched, we provide provocative viewpoints for future expansion.

The concept of killing a tumor in situ without ionizing radiation or surgery is not new, as the quotation from Hippocrates attests. previously, direct visualization was necessary, as in the pouring of liquid nitrogen into the cavity created by a giant cell tumor of bone.² The advent of cross-sectional imaging with ultrasound or CT enabled physicians to precisely and directly place needles percutaneously into solid tumors in almost all regions of the human body. The procedure was initially performed for diagnosis by needle biopsy, but direct therapeutic intervention closely followed.

In 1986, Livraghi and colleagues described the direct injection, under cross-sectional imaging guidance, of chemotherapy into tumors of the liver, pancreas, pelvis, and lung.³ This work was shortly followed by the direct injection of absolute ethanol.⁴ Heat-based ablative technologies had been available for decades and were initially applied to the trigeminal ganglion for treating patients with trigeminal neuralgia.⁵ This same technology was then applied to bone⁶ and eventually led to the treatment of osteoid osteomas.¹ As the RF technology improved, newer devices^7,8 allowed the destruction of larger volumes of tissue, opening up new applications that were quickly applied to liver tumors.

With the creation of cryoprobe technology in the early 1960s⁹ and refinements in the late '70s and '80s, surgeons and radiologists could place probes directly into liver tumors in the operative setting, using ultrasound guidance. Newer percutaneous cryoprobes developed over the past decade have enabled additional clinical applications, including treatment of prostate cancer.¹⁰

Other heat-based ablative technologies, such as laser and microwave, are also being used to treat tumors under image guidance, and they show considerable promise. The ultimate goal of these techniques is to provide excellent local control rates with fast treatment times at reasonable cost. Head-to-head comparisons in the literature are thus far lacking, and this presents a fertile area for image-guided interventional research.

Appropriate patient selection is essential to the success of these new technologies. Similar oncologic principles apply to ablation as to radiation therapy and surgery. Removal or destruction of a local tumor makes sense when tumor staging suggests localized disease or when symptom control or palliation is the goal.

Choosing the appropriate patient also means choosing the appropriate tumor and taking the tumor biology into consideration. Rapidly growing tumors with rapid dissemination characteristics are poor candidates for local therapy. Many patients have comorbid medical conditions that make traditional oncologic treatments such as surgery, radiation, and chemotherapy inappropriate for them. Treating these patients makes sense if tumor control is likely to improve their quality or quantity of life. Implementing local ablative therapy does not make sense if the patient is likely to succumb to an underlying medical condition.

As cancer treatment is a relatively new area for most radiologists, conferring with a team of subspecialists at the tumor board level is an excellent means of acquiring the knowledge and credibility of the other treating physicians. The team approach becomes increasingly important for patients who are candidates for multimodal therapy, given the systemic nature of many cancers and the known synergy of ablative techniques with chemotherapy and radiation.

Since ablative therapy is not extirpative, identifying residual or recurrent disease against the background of treatment effects can be difficult in the early post-treatment period. PET and contrast CT or MRI may identify areas of persistent metabolically active tissue or tumor neovascularity. The precise timing and sensitivity of these techniques has not been defined, but suffice to say that growth in size beyond the postablation baseline examination is more than likely tumor growth, and new metabolically active areas with qualitative and quantitative assessment in the neoplastic range are also likely evidence of progression. Current scientific study on the most appropriate modality and timing of utilization is not yet conclusive. Ongoing multicenter trials have incorporated imaging evaluation as part of the scientific design in the hopes of answering these important questions. As with many patient examinations, definitive answers in equivocal cases can be obtained by biopsy evaluation or additional follow-up over time.

Because the field of image-guided tumor ablation is young, many questions remain unanswered. Early results are very encouraging, however, and the future scientific progress in technology and clinical trials will surely lead to its continued success and implementation.

References

1. Rosenthal DI, Springfield DS , Gebhart MC, et al. Osteoid osteoma: percutaneous radiofrequency ablation. Radiology 1995;197:451-454.

2. Marcove RC, Weis LD, Vaghaiwalla MR. Cryosurgery in the treatment of giant cell tumor of bone. A report of 52 consecutive cases. Cancer 1978;41:957-969.

3. Livraghi T, Bajetta E, Matricardi L, et al. Fine needle percutaneous intratumoral chemotherapy under ultrasound guidance: a feasibility study. Tumori 1986;72:81-87.

4. Livraghi T, Festi D, Monti F, et al. US-guided percutaneous alcohol injection of small hepatic and abdominal tumors. Radiology 1986;161:309-312.

5. Sweet WH, Wepsic JG. Controlled thermocoagulation of trigeminal ganglion and rootlets for differential destruction of pain fibers. J Neurosurg 1974;40:143-156.

6. Tillotson CL, Rosenberg AE, Rosenthal DI. Controlled thermal injury of bone. Report of a percutaneous technique using radiofrequency electrode and generator. Invest Radiol 1989;24:888-892.

7. Goldberg SN, Gazelle GS, Solbiati L, et al. Radiofrequency tissue ablation: increased lesion diameter with a perfusion electrode. Acad Radiol 1996;3:636-644.

8. McGahan JP, Browning PD, Brock JM, Tesluk H. Hepatic ablation using radiofrequency electrocautery. Invest Radiol 1990;25:267-270.

9. Caracalos A, Levita E, Cooper IS. A study of roentgeno-anatomic lesion location and results in cryosurgery of the basal ganglia. St Barnabas Hosp Med Bull 1962;1:24-32.

10. Bahn DK, Lee F, Badalament R, et al. Targeted cryoablation of the prostate: 7-year outcomes in the primary treatment of prostate cancer. Urology 2002;60(2 suppl 1):3-11.

Dr. Dupuy is a professor of diagnostic imaging at Brown Medical School and director of tumor ablation at Rhode Island Hospital in Providence.