Factors that elevate the internal radionuclide and chemical retention, dose and health risks to infants and children in a radiological-nuclear emergency

Promotional etiology for common childhood acute lymphoblastic leukemia: the infective lymphoid recovery hypothesis

This paper speculates on the role of infection in modifying a young child's risk of promoting precursor B-cell acute lymphoblastic leukemia (ALL). It is suggested that the heat shock instigated by infections, particularly in infancy, stimulates Th1 pro-inflammatory cytokines and an apoptosis-inhibitory environment. This infective stress also increases the number of cooperating oncogenic mutations in pre-leukemic cells, especially if the primary adaptive immune response is delayed. The glucocorticoid release that follows leads to acute thymic involution, a decline in antitumor immunity, and maturation arrest of B-lymphocytes. The infective lymphoid recovery hypothesis addresses an apparent contradiction-that a non-hygienic environment primes the adaptive immune response and is protective against childhood ALL, while multiple infections occurring later increase the risk of childhood ALL. In affluent (compared to less-affluent) societies, the characteristic ALL incidence peak in early childhood, and the shortened time to diagnosis, arise from surviving recurrent infections and the accumulated loss and recovery of lymphoid tissue. Evidence supporting the hypothesis, such as the role of lymphoid tissue reconstitution cytokines that stimulate proliferation stress on B-cell progenitors, comes from the study of children with congenital syndromes that are susceptible to leukemia.

Stem cell niches and other factors that influence the sensitivity of bone marrow to radiation-induced bone cancer and leukaemia in children and adults

PURPOSE

This paper reviews and reassesses the internationally accepted niches or 'targets' in bone marrow that are sensitive to the induction of leukaemia and primary bone cancer by radiation.

CONCLUSIONS

The hypoxic conditions of the 10 μm thick endosteal/osteoblastic niche where preleukemic stem cells and hematopoietic stem cells (HSC) reside provides a radioprotective microenvironment that is 2- to 3-fold less radiosensitive than vascular niches. This supports partitioning the whole marrow target between the low haematological cancer risk of irradiating HSC in the endosteum and the vascular niches within central marrow. There is a greater risk of induced bone cancer when irradiating a 50 μm thick peripheral marrow adjacent to the remodelling/reforming portion of the trabecular bone surface, rather than marrow next to the quiescent bone surface. This choice of partitioned bone cancer target is substantiated by the greater radiosensitivity of: (i) Bone with high remodelling rates, (ii) the young, (iii) individuals with hypermetabolic benign diseases of bone, and (iv) the epidemiology of alpha-emitting exposures. Evidence is given to show that the absence of excess bone-cancer in atomic-bomb survivors may be partially related to the extremely low prevalence among Japanese of Paget's disease of bone. Radiation-induced fibrosis and the wound healing response may be implicated in not only radiogenic bone cancers but also leukaemia. A novel biological mechanism for adaptive response, and possibility of dynamic targets, is advocated whereby stem cells migrate from vascular niches to stress-mitigated, hypoxic niches.

Psychosocial considerations for mass decontamination

Mass exposure to explosions, infectious agents, foodborne illnesses, chemicals or radiological materials may require mass decontamination that have critical psychosocial implications for the public and for both traditional and non-traditional responders in terms of impact and of response. Five main issues are common to mass decontamination events: (i) perception, (ii) somatisation, (iii) media role and communication, (iv) information sharing, (v) behavioural guidance and (vi) organisational issues. Empirical evidence is drawn from a number of cases, including Chernobyl; Goiania, Brazil; the sarin gas attack in Tokyo; the anthrax attacks in the USA; Three Mile Island; and by features of the 2003 severe acute respiratory syndrome pandemic. In this paper, a common platform for mass casualty management is explored and suggestions for mass interventions are proposed across the complete event timeline, from pre-event threat and warning stages through to the impact and reconstruction phases. Implication for responders, healthcare and emergency infrastructure, public behaviour, screening processes, risk communication and media management are described.

Requirements for radiation emergency urine bioassay techniques for the public and first responders

Following a radiation emergency, the affected public and the first responders may need to be quickly assessed for internal contamination by the radionuclides involved. Urine bioassay is one of the most commonly used methods for assessing radionuclide intake and radiation dose. This paper attempts to derive the sensitivity requirements (from inhalation exposure) for the urine bioassay techniques for the top 10 high-risk radionuclides that might be used in a terrorist attack. The requirements are based on a proposed reference dose to adults of 0.1 Sv (CED, committed effective dose). In addition, requirements related to sample turnaround time and field deployability of the assay techniques are also discussed. A review of currently available assay techniques summarized in this paper reveals that method development for ²⁴¹Am, ²²⁶Ra, ²³⁸Pu, and ⁹⁰Sr urine bioassay is needed.

A physiological skeletal model for radionuclide and stable element biokinetics in children and adults

A physiological skeletal model (PSM) is described that represents the skeletal uptake, retention, and clearance of both bone-surface-seeking and bone-volume-seeking radionuclides and stable elements. A key objective of the PSM is to model the higher skeletal growth and bone turnover in infants and children (compared to adults) in order to account for their greater uptake and cancer risk from bone-seeking contaminants such as lead and plutonium. The PSM is a compartmental model that allows for the incorporation of organic and inorganic material in the bone volume via quiescent bone surfaces, forming bone surfaces and the lacuno-canaliculi system. The model uniquely incorporates a tertiary phase of mineralization via bone fluids. The PSM's structural concepts and biokinetic parameters--such as realistic mass transfers, organ and tissue masses, and bone remodeling half-times--are selected mainly on the basis of physiological and anatomical criteria. For brevity, model parameter values are evaluated for adults only. The PSM is an improvement on existing skeletal models that are based more on compartment structures and pathways that rendered good fits to biokinetic data rather than on being anatomically and physiologically accurate.