OBJECTIVE: To evaluate the feasibility of sonographically guided radio frequency 
thermal ablation as a minimally invasive method for treatment of unresectable 
recurrent or metastatic tumors in the retroperitoneum and the pelvis, which 
often pose difficult surgical problems.
METHODS: Radio frequency thermal ablation was performed on 7 patients with 
unresectable recurrent retroperitoneal or pelvic tumors from colorectal (n = 4), 
renal (n = 2), and prostate (n = 1) cancers. Under sonographic guidance, a total 
of 11 radio frequency thermal ablation operations were performed by a 
percutaneous or transanal approach.
RESULTS: Three patients were asymptomatic, whereas 4 patients were symptomatic. 
The sizes of the tumors ranged from 29 to 100 mm (mean, 50.5 mm). Radio 
frequency thermal ablation was technically completed in all operations without 
intraoperative complications. The ablation time ranged from 25 to 238 minutes 
depending on the tumor size. There was no mortality. There were postoperative 
complications in 3 operations (27.3%): an enterovesical fistula, a skin burn, 
and fecal incontinence. The hospital stay was generally 0 to 1 day. Tumor marker 
levels decreased after radio frequency thermal ablation in all operations. 
Symptoms of 4 patients were controlled by radio frequency thermal ablation. One 
patient with recurrent renal cancer and uncontrollable hypercalcemia became 
asymptomatic immediately after radio frequency thermal ablation. Local 
recurrence at the radio frequency thermal ablation site occurred in 2 patients 
(28.6%), but these local recurrent tumors were treated effectively by additional 
sonographically guided radio frequency thermal ablation.
CONCLUSIONS: Minimally invasive sonographically guided radio frequency thermal 
ablation is technically feasible for local treatment of unresectable recurrent 
retroperitoneal and pelvic tumors from different origins. Care should be taken 
to avoid thermal injury to surrounding organs. Further study is needed to 
evaluate its safety and efficacy.