1. TNO Centre for Radiological Protection and Dosimetry, PO Box 5815, 2280 HV Rijswijk, The Netherlan ds.
2. Institu te of Haematology, Erasmus University, 3000 DR Rotterdam, The Netherlan ds.
3. Departm ent of Clinical Oncology, Leiden University Medical Centre, 2300 RC Leiden, The Netherlan ds.