Recently, several conditioning regimens did not include total body irradiation (TBI) anymore, especially in the case of young children due to cognitive sequelae and late effects on growth and height. Thus, such effective chemotherapy conditioning regimens were developed to avoid these complications. Busulfan is one of the major drugs used in these treatments, but, is also administered in high dose chemotherapy followed by autograft. In both situations, long term pulmonary side effects were diagnosed in a few cases. Even if the occurrence is not very frequent, the clinical management is a real challenge regarding the reduced quality of life and life expectancy of these patients. Up to now, no correlation was done between respiratory sequelae and busulfan pharmacokinetics. Hence, in the investigators' pediatric onco-hematological unit, a prospective study will begin and last three years to assess the respiratory side effects due to busulfan and their potential links with individual drug pharmacokinetic measures. These results will be compared to patients treated with TBI during the same period of time.