RESUMEN
Radiation dose calculations in nuclear medicine depend on quantification of activity via planar and/or tomographic imaging methods. However, both methods have inherent limitations, and the accuracy of activity estimates varies with object size, background levels, and other variables. The goal of this study was to evaluate the limitations of quantitative imaging with planar and single photon emission computed tomography (SPECT) approaches, with a focus on activity quantification for use in calculating absorbed dose estimates for normal organs and tumors. To do this we studied a series of phantoms of varying complexity of geometry, with three radionuclides whose decay schemes varied from simple to complex. Four aqueous concentrations of 99mTc, ¹³¹I, and ¹¹¹In (74, 185, 370, and 740 kBq mL⻹) were placed in spheres of four different sizes in a water-filled phantom, with three different levels of activity in the surrounding water. Planar and SPECT images of the phantoms were obtained on a modern SPECT/computed tomography (CT) system. These radionuclides and concentration/background studies were repeated using a cardiac phantom and a modified torso phantom with liver and "tumor" regions containing the radionuclide concentrations and with the same varying background levels. Planar quantification was performed using the geometric mean approach, with attenuation correction (AC), and with and without scatter corrections (SC and NSC). SPECT images were reconstructed using attenuation maps (AM) for AC; scatter windows were used to perform SC during image reconstruction. For spherical sources with corrected data, good accuracy was observed (generally within ±10% of known values) for the largest sphere (11.5 mL) and for both planar and SPECT methods with 99mTc and ¹³¹I, but were poorest and deviated from known values for smaller objects, most notably for ¹¹¹In. SPECT quantification was affected by the partial volume effect in smaller objects and generally showed larger errors than the planar results in these cases for all radionuclides. For the cardiac phantom, results were the most accurate of all of the experiments for all radionuclides. Background subtraction was an important factor influencing these results. The contribution of scattered photons was important in quantification with ¹³¹I; if scatter was not accounted for, activity tended to be overestimated using planar quantification methods. For the torso phantom experiments, results show a clear underestimation of activity when compared to previous experiment with spherical sources for all radionuclides. Despite some variations that were observed as the level of background increased, the SPECT results were more consistent across different activity concentrations. Planar or SPECT quantification on state-of-the-art gamma cameras with appropriate quantitative processing can provide accuracies of better than 10% for large objects and modest target-to-background concentrations; however when smaller objects are used, in the presence of higher background, and for nuclides with more complex decay schemes, SPECT quantification methods generally produce better results.
Asunto(s)
Procesamiento de Imagen Asistido por Computador/métodos , Dosis de Radiación , Incertidumbre , Calibración , Humanos , Neoplasias/diagnóstico por imagen , Fantasmas de Imagen , Radiometría , Tomografía Computarizada de Emisión de Fotón Único , Tomografía Computarizada por Rayos XRESUMEN
BACKGROUND: The content of discharge prescriptions/summaries to improve communication about medication provided at discharge has been the subject of recent studies. To date, the authors are not aware of any literature that assesses the need for primary care health professionals to receive information on reasons for drug therapy changes incurred during hospital admission. Owing to increased emphasis on seamless care, patient education, and increased accountability for drug costs, general practitioners (GPs) and community pharmacists may consider the receipt of information on the reasons for drug therapy changes incurred during hospital admission to be an essential requirement. AIM: To determine whether GPs and community pharmacists want, and receive, information on the reasons for drug therapy changes implemented by secondary care. The preferred method of acquiring this information is also investigated. METHOD: A questionnaire was posted to all GPs and community pharmacists within the catchment area of Glasgow Royal Infirmary University NHS Trust. Data were collected between June 1995 and July 1995. RESULTS: Replies were received from 71 (64%) GPs and 33 (80%) community pharmacists. Of the respondents, 96% of GPs and 94% of community pharmacists would like information on one or more reason types for drug therapy changes, but the majority do not receive the desired information. Ninety per cent of GPs and 85% of community pharmacists seek this information of facilitate continuity of patient care. The preferred method of receiving the information is by postal delivery via a modified hospital discharge prescription. CONCLUSION: The existing hospital discharge prescription requires modification to facilitate the completion of the reasons for drug therapy changes. The issue of patient-held cards requires consideration. These factors may facilitate continuity of patient care on hospital discharge.