Objectives:The aim of this study was to develop a methodology for calculating the need for positron emission tomography (PET) scanners in a country and illustrate this methodology for Belgium.Methods:First, levels of evidence were assigned to PET in different indications according to a standard hierarchical classification system. The level reached depends on whether there is evidence on diagnostic accuracy, impact on diagnostic thinking, therapeutic impact, impact on patient outcomes, or

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... fectiveness. Second, the number of patients eligible for PET for each indication was derived from a registry of PET. Third, the number of PET scanners needed in Belgium was estimated for different baseline hypotheses about maximum annual capacity of a scanner and the minimally required level of evidence.Results:The number of PET scanners needed crucially depends on the level of evidence considered acceptable for the implementation of PET: the higher the level of evidence required, the lower the number of PET scanners needed. Belgium needs at least three and at most ten PET scanners. This contrasts with the thirteen currently approved.Conclusions:Scientific evidence and information on the eligible population for a specific procedure are crucial elements for policy makers who wish to make evidence-based decisions about programming and planning of heavy medical equipment.