Objective — to calculate sample size for Return to Normal Daily Life Activity (RNDLA) and additional clinical and technical outcomes for RCT which compare standard Anticoagulant Therapy (AT) with adjunctive Catheter Direct Thrombolysis (CDT) versus AT only. Material and methods. 35 patients was recruited with symptomatic acute lower-extremity proximal DVT. 17 patients underwent AT with adjunctive CDT in-group A and 18 patients received only AT in-group B. Potential primary endpoint proposed RNDLA. Potential secondary endpoints offered pain dynamics, assessed by visual analogue scale, lower limb edema dynamics, efficacy of thrombolysis with contrast venography, residual vein obstruction after 6 months with ultrasonography, post-thrombotic syndrome according Villalta score, and venous clinical severity score with VCSS scale after 6 months. Also planned to evaluate possible complications like PE, recurrent DVT, myocardial infarction, stroke and death. The R Project for Statistical Computings was used for the study. Results. The clinically significant size effect for the potential primer outcome RNDLA was 11 days, Cohen’s d = 0.49. With power 95%, the required sample size should be no less than 228 patients. Conclusion. The pilot study allow determining the potential primary outcome RNDLA and necessary sample size for RCT. As a secondary endpoint, we plan assessment of pain, edema and the technical result CDT.