Variability of the discrepancy between manufacturer and measured CTDI100 values by scanner type, acquisition parameters and phantom size.

According to the EU directive 2013/59, the computed tomography (CT) equipments shall be able to inform the practitioner of parameters for assessing the patient dose. The aim of this study was to measure the accuracy of the CTDI100 with respect to the values stipulated in the manufacturer manual for different manufacturers/models of CT and to assess the impact of acquisition parameters on CTDI100 accuracy. Ten CT from 4 different manufacturers were included in the study. The discrepancy with the manufacturer value CTDI100 was checked with a dosimeter with traceable calibration. Manufacturer values for the CTDI100 were derived from the equipment's manual. The impact of the kVp, CT model, primary collimation and phantom size on the discrepancy of the CTDI100, was assessed by a four-way ANOVA. All the factors had a statistically significant impact on CTDI100 discrepancy (P < 0.05). In a head to head comparison, the greater discrepancies were found on average for 80 kV (15.4 ±â€¯10.7%), sixteen channels CT (10.3 ±â€¯5.1%) and for thick collimations (13.2 ±â€¯6.8%), whilst no significant differences were found between head and body phantoms. For sixteen channels CT and acquisition protocols involving the use of low kV or thick primary collimation, the discrepancies with the manufacturer value CTDI100 can be higher than 20%, which is the suspension level indicated in the EC RP N.162 Publication. This suggests the need of individual calibration of CT X-ray tubes by the manufacturers and the necessity of including this check in the quality control programs for CT.

Radioguided surgery of breast cancer: radiation protection survey.

The aim of this study was to estimate the radioactive risk for surgical staff performing radioguided sentinel lymph node (SN) biopsy and to calculate the contamination level in the operating room for assessment of the possible need for specific radiation protection procedures. We studied 20 patients who were selected for quadrantectomy and SN biopsy. The day before surgery a volume of 0.15 mL of 99mTc-nanocoll was injected: the activity was 3.11 +/- 0.85 MBq in group A (15 pts) and 11.6 +/- 0.6 MBq in group B (5 pts). External radiation to staff was evaluated by measuring the exposure rate in air one hour after radiopharmaceutical administration. The air KERMA rate during surgery was estimated considering the physical decay of 99mTc. Contamination of disposable materials and surgical instruments in the operating room was measured using a contamination monitor, whereas the residual activity in the SN and the injection site was measured with a gamma probe. The exposure rate at 20 cm from the injection site was 0.75 microSv/h when the most radioactive patients (group B) were treated. Contamination in the operating room proved to be negligible. Considering the number of radioguided treatments carried out by a surgeon in one year, an equivalent effective dose of 0.075 mSv was estimated; the recommended dose limit according to the relevant Italian law, DL 230/95, is 1 mSv/yr. Surgical staff therefore do not require a classification of "exposed workers" and there is no need to supply the operating room with special containers for radioactive waste.

Assay of prick test inoculum volume. I. Use and reliability of a gamma camera-based method.

INTRODUCTION: In dermatology and allergy there are clinical research circumstances where very small amounts of substances introduced into the skin have to be measured "in vivo." An example is the assay of reagents injected by prick test. As injected volumes are very small, it is necessary to use indicators that can be measured at very low concentrations. In in vitro studies, gamma-emitting radioisotopes have been shown suitable for use as the indicators. In in vivo studies, except for instruments devised for specific research requirements, the measurement of small sources is taken with a common gamma camera. OBJECTIVE: The purpose of the present study is to evaluate the experimental reliability of a gamma camera-based method to measure microvolumes labeled with radioisotopes and its suitable application in vivo studies. METHODS: Using a solution of 99m Tc-pertechnetate, we prepared, with precision pipettes, some sets of scalar volumes ranging from 1 micro to 200 picoliters, which correspond to activities between some micros and some hundreds of picocuries. The volumes were measured with a gamma camera both with and without a collimator. The overall reliability of the method under different experimental conditions was evaluated for sensitivity, precision, and accuracy. Last, a blind measurement was taken as a final check on the overall reliability of the method. RESULTS: The volume-activity correlation appeared to be linear, with a Spearman coefficient higher than 0.99. The correlation straight lines of the measurements taken with and without a collimator proved that, in both cases, the linearity of the system did not change. The method showed a high degree of precision and accuracy. The maximum variation coefficient never exceeded 1.5% and the standard error 2%. The sampling error of the measured volumes was less than 8% in all the sets: up to 7% was due to the manual operations and to the technical characteristics of the micropipettes. The gamma camera measurement error ranged from 1% to 3%. The blind tests experimentally confirmed the overall reliability of the method. CONCLUSIONS: The method we studied proved highly reliable and inexpensive. Measurement errors are almost exclusively due to sampling errors. The gamma camera is a device any nuclear medicine department is equipped with, and a solution of 99m Tc-pertechnetate is readily available.

Assay of prick test inoculum volume. II. Average values and individual variability.

INTRODUCTION: The amount of reagent introduced into the skin by a prick test is critical in studies on the reproducibility and standardization of the method. OBJECTIVE: The purpose of the present study was to measure the average volume and the individual variability of the inoculum performed with a prick test standardized technique. METHODS: Two hundred forty prick tests--16 inoculations per subject--were performed on the volar sides of arms of 15 healthy volunteers. The tests were performed by a skilled tester whose technical performance complied with the criteria of good reproducibility described in international guidelines. A 1-mm tip standard device and a 50% glycerosaline solution labeled with Tc99m were used for the test. The inoculum size was calculated using a direct assay method based on the gamma camera. RESULTS: The average volume of the prick test inoculum was equal to 0.016 microliters, with a remarkable dispersion of the values around the mean (median, 15906: range, 418 to 82253 picoliters). Further, we observed great variability from one subject to another and great variability in the same subject from one skin site to another. A statistical analysis of the data shows that this variability depends on the individual characteristics of the subjects examined. A skilled tester using a standardized technique is not responsible for significant variability. CONCLUSIONS: Even when performed by a skilled operator and with standardized techniques, the prick test shows great limits of reproducibility, at least as far as the size of the inoculum volume is concerned. The variability of the inoculum depends, in a statistically significant way, on the subject's individual characteristics and therefore can be reduced only within certain limits by the standardization and perfectibility of the technique.