Marie Sydoff

A Compartmental Model for Biokinetics and Dosimetry of 18F-Choline in Prostate Cancer Patients

PET with 18F-choline (18F-FCH) is used in the diagnosis of prostate cancer and its recurrences. In this work, biodistribution data from a recent study conducted at Skåne University Hospital Malmö were used for the development of a biokinetic and dosimetric model. Methods: The biodistribution of 18F-FCH was followed for 10 patients using PET up to 4 h after administration. Activity concentrations in blood and urine samples were also determined. A compartmental model structure was developed, and values of the model parameters were obtained for each single patient and for a reference patient using a population kinetic approach. Radiation doses to the organs were determined using computational (voxel) phantoms for the determination of the S factors. Results: The model structure consists of a central exchange compartment (blood), 2 compartments each for the liver and kidneys, 1 for spleen, 1 for urinary bladder, and 1 generic compartment accounting for the remaining material. The model can successfully describe the individual patients’ data. The parameters showing the greatest interindividual variations are the blood volume (the clearance process is rapid, and early blood data are not available for several patients) and the transfer out from liver (the physical half-life of 18F is too short to follow this long-term process with the necessary accuracy). The organs receiving the highest doses are the kidneys (reference patient, 0.079 mGy/MBq; individual values, 0.033–0.105 mGy/MBq) and the liver (reference patient, 0.062 mGy/MBq; individual values, 0.036–0.082 mGy/MBq). The dose to the urinary bladder wall of the reference patient varies between 0.017 and 0.030 mGy/MBq, depending on the assumptions on bladder voiding. Conclusion: The model gives a satisfactory description of the biodistribution of 18F-FCH and realistic estimates of the radiation dose received by the patients.

ABSOLUTE QUANTIFICATION OF ACTIVITY CONTENT FROM PET IMAGES USING THE PHILIPS GEMINI TF PET/CT SYSTEM.

Positron emission tomography combined with computed tomography (PET/CT) is a quantitative technique suitable for diagnostics and uptake measurements. The quantitative results can be used for the purpose of the calculating absorbed dose to patients undergoing nuclear medicine investigations. Hence, the accuracy of the quantification of the activity content in organs or tissues is of great importance. When using a planar gamma camera and single photon emission computed tomography (SPECT) images, the activity content in organs and tumours has to be determined by the user, using the number of counts in the organs and the efficiency of the camera. However, when using a Philips Gemini TF PET/CT system, the activity concentration in a region of interest (ROI) is given by the system. The reliability of activity concentration values given by the Philips Gemini TF PET/CT system was studied using a Jaszczak phantom containing hot spheres of different sizes; the influence of the ROI size and the impact of organ size, that is the partial volume effect, was investigated with three different lesion-to-background ratios in the phantom. The use of a small ROI size (40 % of the large ROI size, which covered the entire sphere) showed a 15 % improvement in the recovery of the true activity. Small lesion sizes result in large underestimations of the activity concentration values.

Determination of the biodistribution and dosimetry of (123)I-FP-CIT in male patients with suspected Parkinsonism or Lewy body dementia using planar and combined planar and SPECT/CT imaging.

In this study, (123)I-FP-CIT biodistribution and dosimetry was determined in 10 adult male patients using planar gamma camera imaging alone or in combination with single photon emission computed tomography /X-ray computed tomography (SPECT/CT) imaging. Dosimetric assessment using planar plus SPECT/CT imaging resulted in significantly different estimates of organ-absorbed doses compared to estimates based on planar imaging alone. We conclude that the use of complementary SPECT/CT measurements in biodistribution studies is valuable for determining the organ doses more accurately.

Experiences from the production and homogeneity analysis of an AMS 14C sucrose standard for high-activity measurements

Accurate accelerator mass spectrometry (AMS) measurements rely on standards with well-known isotopic ratios. For radiocarbon measurements, a number of standards with different properties are commercially available, of which the IAEA-C6 sucrose standard with a 14C value of 150.61 pMC is the most active. When analyzing biological samples resulting from studies using 14C-labeled substances, the activity content can be up to 100 times this value. Thus, there is a need for a standard material with higher activity content than IAEA-C6 for making accurate AMS measurements on this type of sample. This paper describes the attempts of producing a standard with an activity content of about 10 times modern carbon. The material chosen has to be chemically inert, preferably non-toxic, commercially available in 14C-labeled form, and the activity must be homogeneously distributed within the material. Two different standard materials were considered: urea and sucrose. Sucrose was chosen for the new standard, since it is non-toxic, inexpensive, and organic and on combustion, forms only carbon dioxide (CO2) and water (H2O). In this paper, we discuss our experience in the production and homogeneity analysis of this material, from the crystallization of the sucrose solution to the graphitization of the samples. When using an online combustion method and a septa-sealed vial reduction method, the AMS measurements indicated that the activity was not homogeneously distributed throughout the material. Contrary to this, measurements of the sucrose solution prior to recrystallization indicated that the activity was more homogeneously distributed before than after the recrystallization. In order to determine whether the inhomogeneity depended on the graphitization method (i.e. the combustion or the reduction method) or on the material itself, 3 different graphitization methods and 2 different methods of recrystallization were tested. (Less)

INVESTIGATION OF PARTIAL VOLUME EFFECT IN DIFFERENT PET/CT SYSTEMS: A COMPARISON OF RESULTS USING THE MADEIRA PHANTOM AND THE NEMA NU-2 2001 PHANTOM.

Positron emission tomography combined with computed tomography (PET/CT) is a quantitative technique used for diagnosing various diseases and for monitoring treatment response for different types of tumours. However, the accuracy of the data is limited by the spatial resolution of the system. In addition, the so-called partial volume effect (PVE) causes a blurring of image structures, which in turn may cause an underestimation of activity of a structure with high-activity content. In this study, a new phantom, MADEIRA (Minimising Activity and Dose with Enhanced Image quality by Radiopharmaceutical Administrations) for activity quantification in PET and single photon emission computed tomography (SPECT) was used to investigate the influence on the PVE by lesion size and tumour-to-background activity concentration ratio (TBR) in four different PET/CT systems. These measurements were compared with data from measurements with the NEMA NU-2 2001 phantom. The results with the MADEIRA phantom showed that the activity concentration (AC) values were closest to the true values at low ratios of TBR (<10) and reduced to 50 % of the actual AC values at high TBR (30-35). For all scanners, recovery of true values became closer to 1 with an increasing diameter of the lesion. The MADEIRA phantom showed good agreement with the results obtained from measurements with the NEMA NU-2 2001 phantom but allows for a wider range of possibilities in measuring image quality parameters.