The influence of patient size on the overall uncertainty in radiographic dose audit.

The aim of this work was to investigate the effect of patient and cohort size on the overall uncertainty associated with dose audit using radiography of the abdomen as the exemplar. Water equivalent diameterDwwas used as the surrogate for patient size and its distribution (σ(Dw)) was used to quantify the effect of sample size. The more precise the kerma area product calibration, the more patients are required in the cohort to have the same impact on the overall uncertainty. Patient sample sizes of 300-400 will result in expanded uncertainties approaching the theoretical limit of double the measurement uncertainty when audits are performed with instruments having measurement uncertainties equal to ±7%, ±10% or ±12.5%. By way of example, for a field instrument with a measurement uncertainty of ±10%, a minimum sample size of 350 is required to achieve a total expanded uncertainty of ±21%. In the case of instruments with associated measurement uncertainty of ±3.5%, patient sample sizes of 300-400 will result in expanded uncertainties of approximately ±10%. From review of the literature and comparison with the results obtained here, it is conjectured that for radiographic dose audits of all parts of the trunk the contribution to overall uncertainty due to patient and sample size could be predicted using an indicative value forσ(Dw) of 3.4 where local data is not available.

Developing a method and deriving an uncertainty budget for the internal calibration of dosemeters for radiographic equipment.

Any institution wishing to perform an internal cross calibration of its diagnostic dosemeters should first quantify the uncertainty associated with this to demonstrate that it remains appropriate for the measurements being undertaken.An uncertainty budget for internal cross calibration that covers a range of locally used dosemeters has been derived using the methodology of the International Atomic Energy Agency. The specific internal cross calibration protocol requirements necessary for this uncertainty budget to be valid are discussed.The final quantified uncertainty is 5.31%; this is dominated by the 5% uncertainty associated with the calibration of the reference instrument. The next largest contributions are from differences in temperature and pressure and dosemeter energy dependence.It has been demonstrated that with careful adherence to a well designed internal cross calibration protocol, dosemeters can be calibrated in-house against a calibrated reference dosemeter with very little increase in the associated calibration uncertainty.

Proposals for revised factors in intra-oral radiography shielding calculations.

The current value for weighted average primary plus scatter kerma at 1 m for intra-oral radiography shielding assessment is based on scatter radiation measurements made with the trunk of a RANDO phantom and an assessment of primary transmission that is unverified. Measurements of primary transmission and scatter radiation during intra-oral radiography were made at 30° intervals through a full 360° rotation using two anthropomorphic head phantoms and similar equipment at three different sites. The results suggest that a scatter factor of 5 µGy (Gy cm(2))(-1) and a primary transmission of 0.03% of the entrance surface dose are more appropriate and, therefore, we recommend that the weighted average primary plus scatter kerma used for shielding calculations can be reduced from 1 to 0.5 µGy per exposure at 1 m. This factor will adequately account for exposures made at 60 and 70 kV using a range of intra-oral units.

A comparison of conventional and disposable extended wear contact lenses.

The charts of 126 extended wear contact lens patients (65 disposable and 61 conventional extended wear lens users) were reviewed for subjective and objective contact lens problems. We found that the number of complication events per person per year of lens wear was higher for conventional extended lens wearers than for disposable extended wear patients. There was a trend in both groups toward decreased numbers of complications in the second and third years of lens wear. Within each group, we also examined first time lens wearers and patients with a history of contact lens related complications. Both of these subgroups also fared better with disposable lenses, with fewer complication events per year and fewer complications overall. Of the 20 individual signs and symptoms that were analyzed, 13 occurred more frequently among conventional extended wear lens users; this difference was statistically significant for itching, burning and dryness, poor vision, foreign body sensation, torn and lost lenses, giant papillary conjunctivitis, mucus, and superficial punctate keratopathy. Five signs were more frequent among the disposable extended wear lens users, but the difference was not statistically significant. There were no cases of ulcerative keratitis in either group. The average wearing time was 11.2 +/- 5.9 days for conventional extended wear patients and 6.7 +/- 2.3 days in the disposable group. The difference in wearing time between the two groups may have been a factor in the higher complication rate among conventional extended wear lens patients.

Immunological properties of ferritin during in vitro maturation of human monocytes.

Ferritin in macrophages from human liver and spleen is rich in L subunits but, in the peripheral blood monocytes from which tissue macrophages are derived, the ferritin contains a high proportion of H subunits. We have studied the maturation of monocytes in vitro and the immunological properties of cellular ferritin during this process. Mononuclear cells were isolated from peripheral blood of normal subjects and patients with idiopathic haemochromatosis. Monocytes were obtained by incubation on plastic. The adherent cells were incubated in medium with or without added iron (ferric ammonium citrate) for 20 hours and harvested. Monocytes were also incubated for 7 days before incubation with iron. Ferritin concentrations were determined using immunoassays specific for H and L rich isoferritins. Freshly isolated monocytes were found to have similar concentrations of H- and L-rich isoferritins. Incubation with iron caused an increase in both H- and L-type ferritins. After incubation for 7 d the ferritin present in the normal cell lysates was L-rich and incubation with iron caused accumulation of L-, but not H-type ferritin. Maturation of monocytes is thus associated with the loss of H-rich isoferritins. There were no differences between normal subjects and patients with idiopathic haemochromatosis in ferritin concentrations. In vitro maturation provides an excellent model for studying the developmental control of ferritin synthesis and breakdown.