Diagnostic Nuclear Medicine for Paediatric Patients in Australia: Assessing the Individual's Dose Burden.

We report data for all Australians aged 0-19 y who underwent publicly funded nuclear medicine studies between 1985 and 2005, inclusive. Radiation doses were estimated for individual patients for 95 different types of studies. There were 374 848 occasions of service for 277 511 patients with a collective effective dose of 1123 Sievert (Sv). Most services were either bone scans (45%) or renal scans (29%), with renal scans predominating at younger ages and bone scans at older ages. This pattern persisted despite a 4-fold increase in the annual number of procedures. Younger children were more likely to experience multiple scans, with the third quartile of scans per patient dropping from two to one with patient age. The median effective dose per patient ranged from 1.3 mSv (4-7 y old) to 2.8 mSv (13-16 y old). This large data set provides valuable information on nuclear medicine services for young Australians in the period 1985-2005.

Impact of relative head sensitivity differences in multi-head gamma cameras.

Cerebral perfusion single photon emission computer tomography (SPECT) can be used to identify epileptogenic foci. A (99m)Tc ethyl cysteinate dimer SPECT of the brain showed clinically evident differences in uptake between the CT attenuation corrected image and the Chang attenuation corrected image. The upper right hemisphere of the brain showed apparent diffuse hyperperfusion in the CT attenuation corrected image while the Chang attenuation corrected image, after reconstruction that appears to average projections, showed symmetrical cerebral perfusion. On review of archived patient data, this artefact was also observed in multiple previous cerebral SPECT studies undertaken on the same camera. Phantom investigation was used to identify the cause of the artefact as a difference in relative head sensitivity. The investigation also characterised the extent and nature of this artefact for CT attenuation corrected images, Chang attenuation corrected images and non-attenuation corrected images.

Estimated dose from diagnostic nuclear medicine patients to people outside the Nuclear Medicine department.

Patients undergoing nuclear medicine scans can be a source of radiation exposure for staff, family and the public. In this paper, 12 common nuclear medicine scans are considered. Doses are estimated for a range of scenarios, to hospital staff, to the public and to the patients' co-workers and family. Estimates are based on dose rates measured as patients left the Nuclear Medicine department. Radiopharmaceutical clearance is calculated from biokinetic models described in International Commission on Radiological Protection publications 53, 80 and 106. For all scan types, and all scenarios, doses are estimated to be substantially less than the trigger level of 300 µSv. Within the hospital, Intensive Care Unit staff receive the highest dose (up to 80 µSv) from patients who have had a myocardial scan or a positron emission tomography scan. For out-patients, the highest doses (up to 100 µSv) are associated with travel on public transport (for 4 h) on the same day as the scan.

Histogram matching for the generation of ventilation-perfusion difference images in SPECT lung scanning: a phantom study.

PURPOSE: Diagnosis of acute pulmonary embolism (PE) is commonly done by acquiring SPECT scans of lung ventilation and of lung perfusion. The two image sets are compared, to identify regions which are ventilated but not perfused ("mismatched defects"). This paper describes the application of histogram matching to the calculation of a ventilation/perfusion difference image, and an investigation of the feasibility of the technique using phantom data. METHODS: An empty balloon was inserted into the lung compartment of an anthropomorphic torso phantom. The lungs were filled with polystyrene beads and with water containing 0.20 kBq/ml of (99m)Tc. Two scans were acquired to mimic a matched ventilation/perfusion pair. Then, 30 ml of water containing 0.01 kBq/ml of (99m)Tc was injected into the balloon and the phantom was rescanned. This was repeated four more times, adding 30 ml each time. Each perfusion scan thus had a mismatched defect of a different size. A CT scan was also performed after each perfusion scan, to verify the size and location of the balloon. Histogram matching was applied to each perfusion scan, which was then subtracted from the ventilation scan, yielding a difference image in which voxels with positive values identified mismatched defects. For each scan, a volume of interest (VOI) was automatically generated on the defect and was also copied across to the contralateral side to determine target to background ratios. RESULTS: All mismatched defects were clearly visible in the difference images, including the smallest, which corresponded in size to a small subsegmental defect. Voxel values for the mismatched defects ranged from 17 to 26, compared with contralateral regions, which had voxel values of 0 or 1. CONCLUSIONS: Histogram matching provides a simple, automatic data-driven method for scaling ventilation and perfusion studies without user intervention.

Correlation of various published radionuclide glomerular filtration rate estimation techniques and proposed paediatric normative data.

OBJECTIVE: The aim of this study is to assess the comparability and interchangeability of the radionuclide glomerular filtration rate (GFR) using different published techniques, and propose normative data for paediatrics. METHODS: A total of 476 paediatric oncology patients aged 2-17 years, referred between January 2001 and December 2008 for GFR estimation, were reviewed for any potential cause of renal impairment. Sixty-nine patients met the stringent inclusion criteria, and were included in the study. GFR estimation was carried out using either technetium-99m diethylene triamine penta-acetic acid (99mTc-DTPA) or chromium-51 EDTA (5¹Cr-EDTA). Multiple GFR results were calculated from the same blood sample data (counts/min/ml), according to previously published GFR estimation techniques using one to three blood samples. These techniques were slope-intercept, slope-only and half life. For slope-intercept techniques, GFR was normalized to body surface area or extracellular fluid volume. RESULTS: The GFR values obtained using different techniques were highly variant. The intraclass correlation (ICC) for different methods was moderate (ICC=0.56-0.66). A reliable empiric formula to allow conversion of GFR values from one technique to another could not be derived because of this variability, with some exceptions. 5¹Cr-EDTA yielded the same or lower variability than 99mTc-DTPA. The British Nuclear Medicine Society-recommended method had the lowest coefficient of variation, with a mean value of 116 (SD 22) normalized to 1.73 m² for 5¹Cr-EDTA using two samples. CONCLUSION: The GFR values obtained from different calculation techniques are not readily interchangeable or comparable, with some exceptions. For both 99mTc-DTPA and 5¹Cr-EDTA, the British Nuclear Medicine Society-recommended technique appears to be the most robust, with the least coefficient of variation.

Dosimetry and toxicity of Quadramet for bone marrow ablation in multiple myeloma and other haematological malignancies.

Standard treatment regimens for haematological malignancies include myeloablative chemoradiotherapy and subsequent rescue by stem cell transplantation. However, these treatment regimens have significant associated mortality and morbidity, and disease recurrence remains a problem. One alternative approach is the targeted delivery of radiotherapy to the marrow using a bone-seeking agent labelled with an appropriate radioisotope, with the aim of delivering a potentially ablative radiation dose to marrow while minimising non-haematological toxicity. Pharmacokinetics and radiation dosimetry for a commercial preparation of samarium-153 ethylene diamine tetramethylene phosphonate (EDTMP; Quadramet) were evaluated in 43 tracer (average dose 740 MBq) studies of 42 patients with haematological malignancies. Measurements of 24-h retention were also available following infusion of 18-48 GBq in 15 patients. Quadramet cleared rapidly from the tissue, with a median biological half-life of 1.4 h. Activity taken up by the skeleton was firmly bound, with activity decreasing according to physical half-life at 24 h in 29 of the 43 cases. The percentage activity retained in the skeleton at 24 h with tracer doses was high (62%+/-13%), although this decreased to approximately 30% with therapy infusions. Because of this decrease in retention, the maximum feasible therapy activity for this formulation of Quadramet is 35 GBq. Median absorbed marrow radiation dose was 0.78 Gy/GBq in tracer studies: the decreased retention at high activities means that this corresponds to a median dose of 12 Gy for 35 GBq administered activity. It is possible to use 24-h retention as a rough guide to marrow dose in individual patients. In tracer studies, median bladder radiation dose was 0.22 Gy/GBq and radiation dose to the liver was very conservatively estimated at 0.2 Gy/GBq. After therapy infusions of up to 50 GBq in 37 patients, non-haematopoietic toxicity was not seen in any patient. In addition, myelosuppression was achieved without evidence of myelofibrosis. The residual dose rate to marrow fell to a level acceptable for stem cell re-infusion by 2 weeks after administration.

Estimating uptake in liver and abdominal tumours for radionuclide therapy dosimetry.

Historically, patients for radionuclide therapy have received fixed activities, sometimes normalized to body weight or body surface area. As radionuclide therapy develops, however, practitioners are becoming interested in individualized doses. This requires individual estimates of uptake to be routinely available. Such estimates need not necessarily be highly accurate but the magnitude of associated errors must be known. This paper looks specifically at simple methods for estimating relative (tumour to organ) uptake and also absolute (organ) uptake, for abdominal tumours and the liver. For relative uptake, the ratio of geometric mean counts gives a rough estimate, to within a factor of 2. Absolute liver uptake can be estimated from the geometric mean of liver counts but a correction must be applied for patient attenuation. Such a correction can be calculated solely from the patient's height and weight. The patient weight alone gives a correlation coefficient of 0.86, when plotted against the measured attenuation. However, this correction does not work well for patients heavier than 100 kg. The attenuation index, which is calculated from a patient's weight and height, gives a correlation coefficient of 0.90, for patients ranging in weight from 41 kg to 120 kg.

Measuring and minimizing the radiation dose to nuclear medicine technologists.

OBJECTIVE: Nuclear medicine technologists rely on a single dosimeter to measure their work-related dose. Estimates of whole-body effective dose are based on the assumptions that the radiation is incident from the front and in a uniform beam. We sought to investigate these assumptions and also to quantify doses associated with different activities. METHODS: A single technologist wore 3 electronic dosimeters for 3 mo, at the front waist, the back waist, and the front collar. The technologist also recorded her activities throughout the day. RESULTS: We found that the assumption of an anterior beam held about two thirds of the time, breaking down only when the technologist was receiving lower doses. Overall, the average whole-body dose was estimated correctly by assuming an anterior beam. We also found that irradiation was uniform (i.e., waist and collar badges gave equivalent readings) except when the technologist was performing injections. Then, the collar readings were 1.7 times the waist readings. Finally, average doses were measured for different types of activities. Performing injections registered a dose rate of approximately 2 microSv/h. Doses received while scanning ranged from 0.2 to 2 microSv/h. The average dose for a scan depended not only on the administered activity and isotope but also on the amount of patient contact required. Even for high activities, such as patients who had already received therapy, the dose to the technologist was low for patients requiring little assistance. CONCLUSION: The assumption of anterior irradiation correctly estimates whole-body effective dose. The assumption of a uniform beam is good except when injections are being performed, when the upper torso receives a much higher dose than the waist. Overall, doses to the technologist were found to be 5.4 microSv/d for scanning and 12 microSv/d for injections. These correspond to 1.4 mSv/y and 3.2 mSv/y, respectively, which are comparable to naturally occurring radiation levels and are much lower than regulatory limits. However, if the dose to a particular technologist needs to be minimized (e.g., for a pregnant worker), the most effective strategy is for the technologist to be assigned patients requiring little contact or assistance and, in particular, to avoid administering injections.