In this task, you are given a passage which has a question and the context. You have to generate an answer to the question based on the information present in the context.

Context: To identify subgroups of patients with renal stones 20 mm that are more suitable for extracorporeal shock wave lithotripsy (ESWL) monotherapy.', 'A total of 376 patients with renal stones 20 mm underwent monotherapy with ESWL. The treatment outcome was evaluated after 3 months of follow-up. A stone-free status or fragmentation of stones to 4 mm or smaller was considered efficacious.', 'At 3 months after treatment, the overall stone-free rate was 64.4%, and the efficacy rate was 70.7%. The efficacy rate was 89.4% for patients with a residual stone surface area 50% of baseline after the first ESWL, while the efficacy rate was 32.4% for other patients. The efficacy was 92.2% for stones 400 mm2 and those with lower radiodensity, as determined by a plain (KUB) film.\Question: Do treatment of Renal Stones 20 mm with Extracorporeal Shock Wave Lithotripsy?
For renal stones with a surface area 400 mm2 and a radiodensity equal to or less than that of the 12th rib as determined by a KUB film, ESWL may be considered the first line of treatment, even for stones with a diameter 20 mm. For large stones requiring repeat treatments, the surface area of the residual stones after the first ESWL is a predictor of the final treatment result.