Harmonization of internal dosimetry procedures in Latin America--ARCAL/IAEA project.

Under the auspices of the Regional Coordination Agreement for Latin America, representatives of the eight member states have participated in a project to improve radiological protection for workers exposed to unsealed sources of radiation. The design of the project was based on information obtained from a questionnaire circulated among the participants, from which the initial status of internal dosimetry services in each country was characterised. The objective of the project is to harmonize internal dosimetry procedures, with reference to International Atomic Energy Agency recommendations. After the implementation of new procedures and personnel training, four intercomparison exercises were carried out: measurement of iodine in thyroid phantoms, measurement of gamma emitters in urine samples, measurement of beta emitters in urine samples and internal dose assessments. This project has resulted in important improvements in internal dosimetry services in the region.

A protocol for the calibration of gamma cameras to estimate internal contamination in emergency situations.

The concern about accidents involving radioactive materials has led to the search of alternative methods to quickly identify and quantify radionuclides in workers and in the population. One of the options to face up an eventual demand for mass monitoring of internal contamination is the use of a nuclear medicine diagnostic equipment known as gamma camera, a device used to scan patients who have been administered specific amounts of radioactive materials for medical purposes. Although the gamma camera is used for image diagnosis, it can be calibrated with anthropomorphic phantoms or point sources for the quantification of radionuclide activities in the human body. This work presents a protocol for the calibration of gamma cameras for such application. In order to evaluate the suitability of this type of equipment, a gamma camera available in a public hospital located in Rio de Janeiro was calibrated for the in vivo measurement of 131I. The calibration includes the determination of detection efficiencies and minimum detectable activities for each radionuclide. The results show that the gamma camera presents enough sensitivity to detect activity levels corresponding to effective doses below 1 mSv. The protocol is the basis to establish a network of Nuclear Medicine Centres, located in public hospitals in eight countries of Latin America (Argentina, Brazil, Colombia, Cuba, Chile, Mexico, Peru and Uruguay) and in Spain that could be requested to collaborate in remediation actions in the event of an accident involving incorporation of radioactive materials. This protocol is one of the most significant outputs of the IAEA-ARCAL Project (RLA/9/049-LXXVIII) aimed to the Harmonization of Internal Dosimetry Procedures.

Polyethylene wear and variations in knee kinematics.

A six-station knee wear simulator was used to test a posterior cruciate-retaining total knee arthroplasty design. Six implants each were tested in three groups; low intensity, high intensity, and malalignment using kinematic inputs from normal gait data, more severe loading conditions, and 3 degrees varus malalignment, respectively. For each group, gravimetric wear of the polyethylene inserts was measured for 5,000,000 cycles. Knee wear testing showed significantly different results for the three groups. Low intensity group inserts had mean wear rates of 3.1 (+/- 1.2) mg per million cycles. High intensity group inserts had significantly higher mean wear rates of 7.4 (+/- 2.7) mg per million cycles. Malalignment group inserts had the highest wear rates of 9.2 (+/- 3.3) mg per million cycles. The wear generated in the knee simulator seems to be dependent on the relative motions and loads at the articulating surface. The high intensity groups were subjected to motions that included reciprocating anteroposterior translations and a higher peak axial load than the low intensity group. This resulted in increasing the amount of wear. Varus malalignment also increased the total wear significantly. These results may explain some of the wide variations in wear seen in retrieved knee implants.

Quadriceps moment arm and quadriceps forces after total knee arthroplasty.

Knee prosthetic designs that increase quadriceps moment arm can reduce quadriceps tension and patellofemoral compressive forces. Six knees from cadavers were tested on the Oxford knee rig, which simulates closed chain knee extension under load. Three conditions were tested sequentially for each knee: Normal, Control (implanted with the Osteonics 7000 knee design), and Scorpio (implanted with the Osteonics Scorpio design). The center of flexion-extension of the Scorpio design was 10 mm posterior to that of Control that served to lengthen the quadriceps moment arm. An electromagnetic tracking system measured dynamic knee kinematics, and a uniaxial load cell measured quadriceps tension. The Scorpio design reduced quadriceps tension when compared with the Normal or Control knee ranging from 5% to 20%. This was statistically significant at flexion angles greater than 50 degrees. In three knees, the patellar component was instrumented with a triaxial load cell that measured patellofemoral forces. Patellofemoral forces were lower with the Scorpio design compared with the Control. Increasing quadriceps lever arm reduces quadriceps forces and can facilitate activities of daily living and enhance patient rehabilitation. Reduced quadriceps forces may result in reduced patellofemoral forces that can have a beneficial effect on anterior knee pain, patellar component wear, and loosening.

Thyroid imaging with Tc-99m MIBI in patients with solitary cold single nodules on pertechnetate imaging.

Thyroid imaging was performed in 30 patients with the standard pertechnetate technique, as well as with Tc-99m MIBI using a double-phase acquisition protocol. All patients had normal thyroid function confirmed by hormone measurements and cold solitary thyroid nodules, which were evaluated by pertechnetate scanning. Tc-99m MIBI scans were reported as showing cold (N = 14), warm (N = 7), or hot (N = 9) nodules. Nodule classification was made according to fine needle aspiration biopsy findings in 20 patients. The remaining 10 proceeded to surgery and had histopathologic confirmation of their lesions. Although all cold nodules with Tc-99m MIBI were cystic, six of the warm nodules were benign lesions. No histologically proven benign nodule was hot with Tc-99m MIBI. Of the hot nodules, seven were suspicious for follicular carcinoma with fine needle aspiration biopsy (N = 3), or had histologically proven papillary carcinoma (N = 4). Delayed images in five of seven of these lesions showed nodular retention of the radiopharmaceutical. In conclusion, double-phase Tc-99m MIBI scanning of the thyroid gland could be helpful in the preoperative assessment of patients with cold solitary thyroid nodules in order to evaluate the malignancy probability of these lesions.