Interventional oncology - an emerging field

Image-guided cancer therapy is becoming an important new development in patient care, linking traditional methods with innovative techniques to detect and treat many forms of cancer. Advances in minimally invasive cancer treatments include ablation devices such as radiofrequency, microwave, laser, focused ultrasound and cryoablation, which not only help improve patient care, but also offer the potential to reduce overall healthcare costs.

At the recent Radiological Society of North America (RSNA) meeting held in Chicago from November 26 to December 1 2006, Professor J William Charboneau from the Mayo Clinic College of Medicine, Rochester, Minnesota, US, was invited to present the annual 'New Horizons' lecture. A pioneer in interventional oncology, on receiving this invitation Charboneau said, "This annual lecture given at the RSNA is intended to highlight an important newly emerging direction in healthcare or medical research. Personally, it represents a great honour and privilege to be selected by my peers to represent the thousands of clinicians and researchers working in this exciting rising field of interventional oncology."

According to Charboneau, cancer treatments in the past relied almost entirely on surgical resection, systemic chemotherapy and radiation therapy. Now, due to medical imaging, the combination of new devices and innovative techniques has lead to the evolution of new treatment options. Percutaneously placed thermal ablation devices (eg. radiofrequency), and delivery of new agents and materials with catheter-based techniques have proved effective to destroy cancerous tumours.

In explaining how a new cancer treatment becomes accepted as a standard of care, Charboneau said that it depends upon proving a greater effectiveness and safety, and a lower level of invasiveness and cost than other methods. In addition, the ideal procedure is easy to perform and should be broadly applicable in clinical practice.Date: Feb/2007

Cryoablation of painful metastasis in rib of 30 yr old female. Cryo "ice ball" is seen as oval, well-demarcated hypodense area (white arrow) on CT imaging. Patients pain decreased dramatically following the ablation

"There are few randomised trials comparing the use of image guided ablation with conventional surgery mainly because ablation is a recent alternative. Several series have compared the survival of patients with small hepatocellular carcinoma treated by ablation with previously published surgical series and have showed a remarkably similar survival at five years post-treatment. Quality of life is definitely improved with these minimally-invasive methods over open operation. Morbidity and discomfort are reduced and the patient's return to normal activity is rapid. Quality of life can also be improved for patients who have severe pain due to cancer which has spread to the bone. We have shown that ablation can dramatically reduce a patient's pain and the duration of this effect lasts several years," he said.

Current treatment approaches and future directions
Future directions that will help assure high likelihood of cure depend on three primary factors:
• Greater precision of treatment
• Better treatment devices
• The greater use of combining conventional therapies such as radiation and chemotherapy with the new image-guided ablative methods

Greater precision of treatment
To improve pre-treatment planning, there is a need to increase navigation and guidance. According to Charboneau, current limitations with US [ultrasound], CT and MRI include often poor visibility, restricted real-time visibility due to radiation exposure or imaging characteristics of the targeted lesion, and limited availability of these imaging technologies, respectively. The ideal navigation system should be accurate, operate in real-time, and consistent, he said.

"Greater precision of ablation therapy will arise from improved image-based pre-treatment planning and novel navigation and image guidance methods," explained Charboneau. "Navigation will improve because of increasing use of 'fusion imaging' whereby CT/MR/PET images are fused with real-time US imaging to increase treatment targeting and accuracy. We will also see increasing use of CT/MR guided robotics to more accurately place ablative devices than current methods which greatly depend on operator skill and experience."

Robotic surgical systems, such as the da Vinci Surgical System (Intuitive Surgical) is powered by robotic technology and allows the surgeon's hand movements to be scaled, filtered and translated into precise movements of micro-instruments within the operative site. The magnified, 3D view the surgeon experiences enables them to perform precise surgery in complex procedures through small surgical incisions. Charboneau explained that similar such technology when applied to percutaneous ablation treatments enables precise placement for:
• Small masses eg. adrenal tumour
• Moving targets eg. lung nodules during respiration
• Large masses eg. tumours requiring multiple applicators for coverage

"Image fusion plus robotics will improve accuracy in the future," stated Charboneau.

Better treatment devices
Currently, radiofrequency, cryoablation and laser based methods are in their second or third generation of technological maturity, said Charboneau. "In the next few years we will see the maturation of first generation ablation methods utilising microwave and focused ultrasound. One interesting advance will be steerable energy delivery for more effective and safer treatment." Such steerable energy could see the development of microwave technology targeting ablation more precisely while avoiding adjacent critical structures. MRI-guided and monitored high intensity focused ultrasound allows tumour ablation without the need for a skin puncture - systematic repeated delivery of steerable focused sound waves destroy a precise volume of tissue without harming surrounding structures. Future advances of focused ultrasound will see electronically controlled steerable acoustic elements allowing an increase in access to targets in difficult to treat areas such as the liver which is covered by overlying ribs.

Increasing use of combination therapies
"The synergy of combination therapy offers exciting opportunities to further improve effectiveness of ablative therapies," Charboneau said. As an example, he further explained that the simple addition of ablation plus local radiation therapy has been demonstrated to increase survival of patients with lung cancer compared to radiation therapy or ablation therapy alone.

"Current research of more revolutionary combinations include the use of ablation with chemotherapeutic drugs that are heat-activated at elevated temperatures. This approach allows a high concentration of a chemotherapeutic agent at the site of malignancy while avoiding adverse systemic side effects," he said. "Current research is examining the use of local ablation to stimulate the patient's immune system. Ablation may result in both destruction of the primary treated lesion, while at the same time producing a systemic response against distant metastases."

Image-guided cryoablation
In addition, Charboneau and colleagues have evaluated the safety and effectiveness of image-guided cryoablation for the palliation of painful metastases involving bone that had failed conventional therapies, in the study 'Painful metastases involving bone: percutaneous image-guided cryoablation - prospective trial interim analysis'.

Dr Matthew Callstrom, (diagnostic radiologist, Rochester, Minnesota) and Charboneau reported that over an 18 month period, 14 patients (eight men, six women; age range, 21-72 years; mean age, 54 years) with one or two painful metastatic lesions involving bone, were treated with percutaneous cryoablation. Treated lesions were 1-11cm in diameter and before cryoablation, the mean score for worst pain in a 24-hour period was 6.7 of 10 (measured with the Brief Pain Inventory). The results demonstrated that after four weeks of treatment the score decreased to 3.8 (p = .003). It was also reported that all eight patients for whom narcotics were prescribed prior to the procedure reported a reduction in these medications after cryoablation.

These findings indicate that the treatment is effective and durable. They are currently preparing to initiate a new multi-centre randomised trial to compare image-guided cryoablation with radiation therapy for the treatment of painful metastases. This study will involve the treatment of 140 patients across the country and should be completed within three years.

"This study will determine if cryoablation is a better treatment than radiation therapy for patients that develop painful metastases," said Charboneau.