***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: BACKGROUND AND PURPOSE  Percutaneous nephrolithotomy ( PCNL ) can be done in patients who have previously had open nephrolithotomy . Currently , dilatation of the nephrostomy tract is achieved using an Amplatz renal dilator or telescopic metal dilators in these patients . The aim of this study was to compare the safety and efficacy of the " one-shot " procedure in patients with previous open nephrolithotomy with those of the current telescopic technique . PATIENTS AND METHODS Thirty-one patients with past history of open surgery for kidney stone disease underwent PCNL at our institution from February 2006 to March 2007 . Patients were r and omly divided into two groups according to dilation technique used : group A ( telescopic procedure ) and group B ( one-shot procedure ) . X-ray exposure , blood loss , and complications were evaluated . RESULTS No significant difference in hemoglobin decrease was seen in the two groups . The stone-free and complication rates were the same in the two groups . Fluoroscopy time during the one-shot procedure was significantly shorter than that of the telescopic procedure ( P < 0.000 ) . CONCLUSION Our experience indicated that the one-shot procedure is feasible in patients with previous open nephrolithotomy . It is as safe and effective as the telescopic procedure , with significant reduction in x-ray exposure PURPOSE To assess the feasibility of one-stage acute dilation of the nephrostomy tract with a 30F Amplatz dilator in patients who are c and i date for percutaneous nephrolithotomy ( PCNL ) regardless of whether there is a previous renal scar to make the procedure less time consuming and more cost effective . PATIENTS AND METHODS The outcomes of one-stage tract dilation for PCNL in 100 consecutive patients with and without a history of ipsilateral open stone surgery ( OSS ) , treated by one surgeon , were examined prospect ively . Forty-six patients ( group 1 ) had a history of ipsilateral OSS , and 54 patients ( group 2 ) did not have this history . Demographic data as well as intraoperative information , such as access time and radiation exposure time during access , were recorded . The success of the access technique and its bleeding complications were analyzed between the two groups . RESULTS By applying a " one-stage " technique , the targeted calix could be entered with a success rate of 93 % . There was no difference in the procedural success rate between groups 1 and 2 ( 93.5 % v 92.6 % , respectively ) . All seven failed attempts ( 7 % ; three with previous OSS ) were managed successfully using an Alken dilator to gain access to the proposed calix in the same session . Previous OSS did not impact access time , radiation exposure time during access , postoperative hemoglobin drop , and bleeding complications . There were no visceral and vascular injuries . CONCLUSIONS One-stage tract dilation for PCNL is a safe and effective method in almost every adult patient PURPOSE To compare the effects of one-stage vs gradual dilation techniques during  percutaneous nephrolithotomy ( PCNL )  on postoperative renal scar formation and overall renal function . PATIENTS AND METHODS Of 152 adult patients who underwent surgery during the study period , 48 were r and omized into two groups . In group 1 ( n=19 ) , gradual tract dilation with Alken metallic dilators was used , and in group 2 ( n=29 ) , one-stage tract dilation was used . We compared patient demographics , intraoperative and preoperative parameters , postoperative overall renal function , and renal scar formation on the target renal pole . RESULTS Access time ( P=0.001 ; 95 % confidence interval [ CI ] : 3.19 - 6.30 ) and radiation exposure during access ( P=0.03 ; 95 % CI : 0.03 - 0.66 ) were significantly shorter in group 2 . In group 1 , the decrease in mean technetium-99 m dimercaptosuccinic acid ( 99m-Tc DMSA ) uptake from 44.1±20.1 % to 43.4±19.6 % 4 weeks postoperatively ( -0.7%±0.5 % ; P=0.27 ; 95 % CI : -0.56 - 1.93 ) was not significant . In group 2 , however , there was a significant decrease in post-PCNL 99m-Tc DMSA uptake 2 ( -2.4±0.3 % , from 50.1±13.5 % to 47.7±13.8 % ; P=0.001 ; 95 % CI : 1.13 - 3.66 ) . Four weeks after surgery , new scar formation or progression of the preoperative scar at the site of access were seen in 14 of 29 ( 48.3 % ) patients who were treated with one-stage dilation whereas only 2 of 19 ( 11.0 % ) patients who were treated with gradual dilation developed new scarring at the access site ( P=0.007 ) . CONCLUSION Although the one-stage tract dilation technique reduced radiation exposure and access time , in the short term , it may cause more parenchymal damage than the gradual dilation technique 
    Output:
    
Our results show that One-shot dilation is an effective and safe procedure for tract creation in PCNL , with shorter access time and X-ray exposure time and without increased complications .