137 Determinants for side effects 4 SUPPLEMENTAL METHODS ALL-11 treatment ALL-11 maintenance treatment contained 28 three weekly treatment cycles. Patients were enrolled in the study after completion of doxorubicin (administered on the first day of the first four treatment cycles). Patients could be included at any cycle thereafter, that is, some patients started directly after cessation of doxorubicin (beginning of maintenance treatment) and some patients started later during maintenance treatment. Dexamethasone 6 mg/m2/ day was administered for 5 consecutive days at the beginning of each treatment cycle. Patients also received vincristine once every three weeks, methotrexate once per week and 6-mercaptopurine once per day, in dosages as described in the Dutch Childhood Oncology Group ALL-11 protocol. Depending on randomization, patients also received asparaginase once every three weeks till week 15 or 27 of maintenance treatment. Determinants Disease characteristics CNS involvement was dichotomized into present or absent. CNS involvement was defined as CNS-3 (a non-traumatic lumbar puncture (LP) with >5 white blood cells per microliter in the cerebrospinal fluid with identifiable leukemic cells), intracerebral or meningeal mass, cranial nerve palsy or retinal involvement) or a traumatic LP with leukemic cells (TLP+). Both patients with CNS involvement and a TLP+ receive two additional intrathecal administrations during induction treatment which may potentially increase the risk of neurobehavioral side effects. Parent characteristics Information regarding parental factors was extracted from a general questionnaire parents completed upon participation in an online quality of life platform (KLIK).56 This questionnaire was not available for all included patients. Parenting stress We used the NOSI-K (Nijmeegse Ouderlijke Stress Index Korte versie, adapted from the Parenting Stress Index) 30,31 to measure parenting stress. The NOSI-K has been found to have a good internal validity, in the present study the reliability coefficient was 0.92 on T1 and 0.96 on T2. We also used the Distress Thermometer for parents (DT-P)32, which is a validated questionnaire and consists of three parts: 1) a thermometer (visual analogue scale) ranging from 0 (no distress) to 10 (extreme distress), 2) a problem list about everyday problems over the past week across six domains (practical, social, emotional, physical, cognitive and parenting problems): the total score adds all domains (higher score reflects more problems), and 3) additional
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