Real-Time Magnetic Resonance Imaging–Guided Focal Laser Therapy in Patients with Low-Risk Prostate Cancer

Excerpts below:

Abstract

Two patients with low-risk prostate cancer (PCa) were treated with outpatient in-bore magnetic resonance imaging (MRI)–guided focal laser ablation.

The tumor was identified on MRI. A laser fiber was delivered via a catheter inserted through a perineal template and guided to the target with MRI. The tissue temperature was monitored during laser ablation by MRI thermometry. Accumulated thermal damage was calculated in real time. Immediate post-treatment contrast-enhanced MRI confirmed devascularization of the target. No adverse events were noted. MRI-guided focal laser therapy of low-risk PCa is feasible and may offer a good balance between cancer control and side effects.

Once the catheter reached its target, the metal trocar was replaced by an optical fiber with a 1-cm-long cylindrically diffusing tip attached to a 980-nm diode laser (Visualase Inc, Houston, TX, USA).

During laser ablation, temperature was measured simultaneously on five 3-mm-thick image slices that covered the target volume (Fig. 5a). The thermometry scan was repeated every 6 s.

Fig. 5 (a) Tissue temperature map measured by magnetic resonance thermometry (echo planar imaging with multiphase; field of view: 25 × 25 cm; matrix 256 × 256; number of excitations: 1; repetition time: 545 ms; echo time: 20 ms; flip angle: 20°; slice thickness: 3 mm) during laser ablation; (b) a map of the tissue volume exceeding the threshold damage for coagulation was superimposed on the anatomical image, with the pink line measuring the maximum diameter of the ablated tissue.

The MRI thermometry software (Visualase, Inc, Houston, TX, USA) allowed us to monitor temperature at specific points in the tissue. The temperature at those points was used as a feedback to control the laser. During the laser heating, the temperatures at the border of the rectal wall and urethra were monitored and maintained at safe levels by shutting down the laser automatically when the temperature at these critical points exceeded 45 °C. Thermal damage was calculated using an Arrhenius formula. Temperature and damage maps were superimposed onto anatomic images (Fig. 5b). Once the desired volume of tissue destruction was achieved, laser power was stopped.

The patients were discharged home within 3 h. MR scans performed 2 wk post-treatment showed no evidence of complications with preservation of rectum and neurovascular bundles. No adverse effects were noted at ≤1 mo after treatment. Six-month follow-up biopsies are pending.

Outpatient MRI-guided FLT as used in the present study allows for visualization of the tumor; real-time guidance of the thermal device to the target; monitoring and control of the zone of ablation and surrounding tissue during treatment; and the ability to immediately confirm the success of the treatment and, if necessary, immediately repeat therapy. The required skills are common to other minimally invasive procedures, resulting in a short learning curve for the surgeon. Refinement of this outpatient procedure may result in an inexpensive, minimally invasive alternative to current active therapies. Further trials will be necessary to define the safety and oncologic efficacy of this therapy, but our early results are promising.

Acknowledgment

The authors would like to thank Drs. Ashok Gowda and Roger McNichols of Visualase Inc., Houston, Texas, USA, for generously supplying the laser and magnetic resonance thermometry system and for their technical support of this study.

Read the full article case study.

Laser Ablation of Liver Metastases from Colorectal Cancer with MR Thermometry: 5-Year Survival

Purpose

To determine technical success, technique effectiveness, complications, and survival after laser ablation of liver metastases from colorectal cancer.

Materials and Methods

Eighty-seven consecutive patients (65 men and 22 women; mean age, 62.8 years) with 180 liver metastases from colorectal carcinoma were included between 1998 and 2005. They underwent laser ablation with magnetic resonance (MR) thermometry in 170 sessions. Indications for laser ablation were locally unresectable tumors (16.1%), metastases in both liver lobes (34.5%), and refusal of surgery and/or general contraindications to surgery (49.4%). Technical success, technique effectiveness, and complication and survival rates were evaluated retrospectively.

Results

Technical success was achieved in 178 of 180 sessions (99%). Follow-up after 24–48 hours demonstrated an effectiveness rate of 85.6%. Local tumor progression rate was 10% after 6 months. Major complications included large pleural effusion, large subcapsular hematoma, abscess, large pneumothorax, pleuritis with fever, intrahepatic hemorrhage, and biloma. Mean survival from the time of diagnosis of the primary tumor was 50.6 months for all patients treated (95% CI, 44.9–56.3 months). Median survival time was 54 months and survival rates were 95.7% at 1 year, 86.2% at 2 years, 72.4% at 3 years, 50.1% at 4 years, and 33.4% at 5 years. The mean survival time after the first treatment was 31.1 months (95% CI, 26.9–35.3 months).

Conclusions

Laser ablation of liver metastases of colorectal cancer with MR thermometry appears safe and efficacious. Although the results are encouraging, direct comparison with other ablative modalities in a prospective clinical trial would be necessary to definitely show one modality is superior.

Source:
Journal of Vascular and Interventional Radiology, Volume 20, Issue 2, Pages 225-234 (February 2009)

Liver tumours treated effectively by MR-guided laser ablation

20 December 2005

Destruction of cancerous liver tissue by laser light guided by magnetic resonance (MR) imaging was found to be as effective as traditional surgery for some patients, in a large-scale, 12-year study in Germany.

In the largest study of its type with the longest follow-up, 839 patients at the University of Frankfurt in Germany received MR-guided laser-induced thermotherapy (LITT) for the treatment of liver tumours resulting from colorectal cancer. Between 1993 and 2005, the researchers treated 2,506 liver tumours and tracked survival rates to evaluate the long-term results of the procedure. The average survival rate from the date of diagnosis was 3.8 years, which compares favourably to survival rates after traditional surgery (approximately 1.5 to 5.0 years). The study was presented at the annual meeting of the Radiological Society of North America (RSNA).

In LITT, also known as laser ablation, laser light is used to destroy tumour tissue. According to the study’s lead author, Martin Mack, M.D., laser ablation has many advantages over other treatment methods.

“Traditional surgical resection has higher morbidity and mortality rates than laser ablation,” said Dr. Mack, an associate professor in the department of diagnostic and interventional radiology at the University of Frankfurt. “Laser treatment can be done on an outpatient basis under local anaesthesia. Typically, the patient stays only a couple of hours, instead of a couple of weeks in the hospital after surgical liver resection,” he said.

Laser ablation can be used to treat tumours that occur in both halves of the liver — often during the same treatment — which is practically impossible in a traditional surgery where typically only the left or right lobe is resected. If new tumours are found during follow-up exams, it is much easier to repeat laser treatment than to subject the patient to another open surgery.

Laser ablation also holds advantages over radiofrequency ablation, another minimally invasive method of treating liver tumours, because it can be applied to different parts of the liver simultaneously and can be used with MR guidance to provide the radiologist with an accurate image of the tumour for precise targeting throughout the procedure. Radiofrequency ablation can only treat one tumour at a time and cannot be used with continuous MR monitoring.

Dr. Mack believes that laser combined with MR guidance will have wide-ranging impact on the treatment of tumours throughout the body, and may one day replace traditional surgery as the gold standard of treatment.

“Many surgeons are already performing local ablation instead of resection, because they have already recognized the positive effect of local ablation,” he said. “I believe that minimally invasive tumour ablation together with chemotherapy will play the most important role in the treatment of tumours in the years to come.”

Source: MTB Europe – Technology For Healthcare