From May 2000 to March 2007, sixty-five patients with primary lung malignancies were treated with RFA (n=56) or PTC (n=9) with CT-guidance at Chonbuk National University Hospital. Indications for these ablative therapies were pulmonary malignant tumors in patients with medical comorbidities, pulmonary compromise, or refusal of surgery. This study was performed with the approval of the institutional ethics committee, and written informed consent had been obtained from every patient before the initiation of treatment.
One radiologist performed all procedures on inpatients who had fasted for 12 hours. The RFA was performed with 17-gauge, single or clustered internally cooled radiofrequency electrodes. Once proper electrode positioning was confirmed, we attached the electrode to a 500-kHz monopolar radiofrequency generator (CC-1, Radionics, Burlington, Massachusetts, USA) that produces an output of 150–200 W. Tissue impedance was continuously monitored using the circuitry incorporated in the generator. At the end of each treatment, the perfusion was stopped and the maximal temperature was recorded. If the temperature exceeded 60°C, the electrode was withdrawn in increments of 1 cm up to the length of the active tip; at the same time, the intratumoral temperature was measured. After the first treatment, if the maximal intratumoral temperature did not exceed 60°C, an additional treatment was performed at the same site. Based on descriptions on tumor ablation performed in other organ systems, we chose to apply radiofrequency for 12 minutes during the initial ablation and for 6–12 minutes during subsequent ablations, with a maximum peak current of 1,000–2,000 mA and 80–150 W. After the ablation procedure, the electrode was withdrawn without cauterizing the probe tract.
To perform PTC, we used argon: helium-based system and 17-gauge cryoneedle (IceRodTM, Oncura, Plymouth Meeting, Pennsylvania, USA). This instrument was used for freezing the high-pressure argon gas and thawing helium gas by means of Joule-Thompson principal. After identification of tumor location, treatment area was prepared and draped in sterile manner. According to the size of the tumor, two cryoprobes were inserted at the center of tumor, and then performed cryoablation cycle that is consisted of freezing and thawing. We chose to apply PTC for 50 minutes during the initial ablation
All patients underwent contrast-enhanced helical CT within 1 week before ablation, immediately (within 30 minutes) after RFA or PTC, and 1 month later. Treatment efficacy was assessed on the basis of the post-treatment contrast-enhanced CT scans. All of the areas that did not display contrast enhancement within the boundaries of the treated area after the contrast agent administration were considered as complete ablation. Ablated tissue and the tumor regions that showed enhancement were considered as partial ablation. Repeated contrast-enhanced helical CT examinations were performed at 3-month intervals. We evaluated minor and major complication after RFA or PCT at follow-up.
We used SPSS statistical software (version 13.0, SPSS, Chicago, Illinois, USA). The Kaplan-Meier curve was used to estimate survival function for survival rate. Comparisons of survival functions were performed by using the log-rank test. To assess differences of the rate of complete ablation according to tumor size, we analyzed using chi-square test. Cox proportional hazard regression was also used to examine interactions among potential covariates. For all statistical analyses, p-value less than 0.05 was considered to indicate a statistically significant difference.