Intermittent pneumatic compression versus additional prophylaxis with enoxaparin for prevention of venous thromboembolism after colorectal cancer surgery in Chulabhorn hospital

Interventions: Start IPC + Enoxaparin in 24-48 hour after surgery and continue to 4weeks Perform U/S DVT both at 5-7 day after operation,Start only IPC until fully ambulation Perform U/S DVT both at 5-7 day after operation;Prevention,Prevention;IPC + Enoxaparin,IPC only Primary outcome(s): DVT 5-7 day after operation Yes/No (Ultrasound),DVT 1 month Yes/No (ultrasound)