An analysis of 45 years of reported overexposure incidents in Texas, 1956 to 2001.

Sources of ionizing radiation are commonly encountered in a wide variety of modern work settings. The controls in place to ensure the safe use of these sources have proven to be quite effective, as events involving occupational doses in excess of established limits are quite rare. Nonetheless, instances of doses in excess of established limits, commonly referred to as "overexposures," do occur, but the rarity of such events has resulted in a body of scientific knowledge that consists essentially of sporadic case reports. In this study, incident reports describing radiation overexposure events recorded in Texas from the years 1956 to 2001 were obtained and recorded into a computerized database using a pre-established set of codes. The data were then analyzed for the identification of possible trends or commonalties. During the 45-y period of study, overexposure events accounted for 50% (n = 3,796) of all the radiation-related incidents recorded in Texas for the time period (n = 7,534). Of the overexposure events, 65% (n = 2,342) resulted in the actual deposition of energy in the individual exposed. The remainder were determined to be doses recorded only by a personal dosimetry device. In most of the cases where doses were actually delivered to an individual, the doses were less than 0.05 Sv (5 rem). In only 0.5% of the cases (n = 13) were doses greater than 1 Sv (100 rem). The predominant sources reported as involved in the events included 192Ir, 60Co, and 137Cs. The information derived from the analysis may serve as a basis for a variety of interventions, such as preventative education activities, regulatory modifications, and the possible re-design of equipment identified as commonly associated with such events. The results of the study can also assist in the training of health care providers, as the recognition of common causes and sources of overexposures and subsequent treatments can be forecasted and summary treatment protocols developed.

Massive thymic hyperplasia.

Massive thymic hyperplasia is an extremely rare form of true thymic hyperplasia most often described in infants and children. Hyperplasia of this order is not known to occur in any other organ, and its etiology and prognostic significance remain unknown. As there is no accurate way of preoperatively differentiating massive thymic hyperplasia from other tumors of the thymus and anterior mediastinum, we advise excision in all cases for histological analysis and relief of mediastinal compression. This description of 4 cases updates the 30 previously reported cases, and includes a literature review.