Development and validation of a GEANT4 radiation transport code for CT dosimetry.

The authors have created a radiation transport code using the GEANT4 Monte Carlo toolkit to simulate pediatric patients undergoing CT examinations. The focus of this paper is to validate their simulation with real-world physical dosimetry measurements using two independent techniques. Exposure measurements were made with a standard 100-mm CT pencil ionization chamber, and absorbed doses were also measured using optically stimulated luminescent (OSL) dosimeters. Measurements were made in air with a standard 16-cm acrylic head phantom and with a standard 32-cm acrylic body phantom. Physical dose measurements determined from the ionization chamber in air for 100 and 120 kVp beam energies were used to derive photon-fluence calibration factors. Both ion chamber and OSL measurement results provide useful comparisons in the validation of the Monte Carlo simulations. It was found that simulated and measured CTDI values were within an overall average of 6% of each other.

The skin lesions of neural leprosy. III. Observations in China

The results of a study of leprides in 35 cases of leprosy, from which 39 biopsy specimes were taken, are reported. All but one of the lesions from 31 cases (excluding 4 cases classed as atypical) were clinically simple tuberculoid, or more or less retrogressed, falling into the classification of leprides developed in the course of the present series of studies. Histologically all of them, with the exception mentioned, showed tuberculoid changes in some degree, thus agreeing with the findings of the preceding study of this series. From the number of cases with clinically tuberculoid lesions of different varieties and in different stages (23 out of about 225 cases examined) it is evident that this form is fairly common in China, at least in the southern region. At least 7 cases were or had been of the major form. Several had an interesting "band-like" form of lesion not seen in the Cebu group but observed elsewhere. The more marked forms of the tuberculoid lesions were found in clinic cases; they are apparently rare in old institutionalized cases. A suggestion of a sex influence has been noted, the major tuberculoid lesions being almost entirely in males and the active minor forms predominating in females in this small group. Certain of the cases exemplify the lack of any sharp separation between those with major and with minor lesions, and also between those with minor and with simpler lesions. Other cases exemplify the frequent difficulty of determining the severity of face lesions from outward appearances. One lesions (from the chin) showed nothing but banal chronic inflammatory changes. Certain others in which such changes (chiefly lymphoid infiltration) were marked or predominant seemed to be incompletely differentiated but essentially tuberculoid in nature. The significance of variations in lymphoid-cell content, both in otherwise typical tuberculoid lesions and in those suspected of undergoing transformation to lepromata, requires elucidation. There is reason to believe that slight marginal erythema does not necessarily imply activity (i.e., progression) any more than lack of it necessarily implies quiescence. Superficial atrophy of the skin is discussed. The degree of that condition is apparently dependent upon several factors and does not necessarily indicate the original clinical grade of a retrogressed lesion. Enlargement of cutaneous nerves of a degree probably due to necrosis was observed in four cases...