PROCEDYTE: Depocyte® Administration (Liposomal Cytarabine) as Prophylaxis of Neuromeningeal Infiltration in Acute Lymphoblastic Leukemia

The primary objective is: * To determine the efficacy and safety of DepoCyte®, as the only intrathecal (IT) prophylaxis of neuromeningeal relapse for patients between 16 and 30 years old diagnosed with acute lymphoblastic leukemia of standard risk treated with the PETHEMA LAL-RI-08 Protocol Chemotherapy schedule. The secondary objectives are: * To evaluate the tolerability of IT DepoCyte® as CNS prophylaxis of CNS via IT for patients between 16 and 30 years old with ALL of standard risk. * To compare the frequency of relapse in CNS for patients between 16 and 30 years old with standard risk ALL treated with the PETHEMA LAL-RI-08 Protocol Chemotherapy schedule and receiving DepoCyte® as the only IT CNS prophylaxis, with that observed in an historic group of patients of identical risk that were treated with the PETHEMA LAL-RI/96 protocol (same systemic chemotherapy and double administration of triple intrathecal chemotherapy) * To evaluate the frequency of systemic relapses of standard risk ALL patients between 16 and 30 years old treated with the PETHEMA LAL-RI-08 Protocol and who receive DepoCyte® as the only IT prophylaxis of CNS involvement and to compare with those observed in the identical risk patients treated with PETHEMA LAL-RI/96 protocol (same systemic chemotherapy and double administration of triple IT chemotherapy)