Kidney dynamic SPECT acquisition on a CZT swiveling-detector ring camera: an in vivo pilot study.

BACKGROUND: Large field of view CZT SPECT cameras with a ring geometry are available for some years now. Thanks to their good sensitivity and high temporal resolution, general dynamic SPECT imaging may be performed more easily, without resorting to dedicated systems. To evaluate the dynamic SPECT imaging by such cameras, we have performed an in vivo pilot study to analyze the kidney function of a pig and compare the results to standard dynamic planar imaging by a conventional gamma camera. METHODS: A 7-week-old (12 kg) female Landrace pig was injected with [99mTc]Tc-MAG3 and a 30 min dynamic SPECT acquisition of the kidneys was performed on a CZT ring camera. A fast SPECT/CT was acquired with the same camera immediately after the dynamic SPECT, without moving the pig, and used for attenuation correction and drawing regions of interest. The next day the same pig underwent a dynamic planar imaging of the kidneys by a conventional 2-head gamma camera. The dynamic SPECT acquisition was reconstructed using a MLEM algorithm with up to 20 iterations, with and without attenuation correction. Time-activity curves of the total counts of each kidney were extracted from 2D and 3D dynamic images. An adapted 2-compartment model was derived to fit the data points and extract physiological parameters. Comparison of these parameters was performed between the different reconstructions and acquisitions. RESULTS: Time-activity curves were nicely fitted with the 2-compartment model taking into account the anesthesia and bladder filling. Kidney physiological parameters were found in agreement with literature values. Good agreement of these parameters was obtained for the right kidney between dynamic SPECT and planar imaging. Regional analysis of the kidneys can be performed in the case of the dynamic SPECT imaging and provided good agreement with the whole kidney results. CONCLUSIONS: Dynamic SPECT imaging is feasible with CZT swiveling-detector ring cameras and provides results in agreement with dynamic planar imaging by conventional gamma cameras. Regional analysis of organs uptake and clearance becomes possible. Further studies are required regarding the optimization of acquisition and reconstruction parameters to improve image quality and enable absolute quantification.

Evaluation of safety margins for cone beam CT-based adaptive prostate radiotherapy.

Adaptive radiotherapy is characterized by the use of a daily imaging system, such as CBCT (Cone-Beam Computed Tomography) images to re-optimize the treatment based on the daily anatomy and position of the patient. By systematically re-delineating the Clinical Target Volume (CTV) at each fraction, target delineation uncertainty features a random component instead of a pure systematic. The goal of this work is to identify the random and systematic contributions of the delineation error and compute a new relevant Planning Target Volume (PTV) safety margin. 169 radiotherapy sessions from 10 prostate cancer patients treated on the Varian ETHOS treatment system have been analyzed. Intra-patient and inter-patient delineation variabilities were computed in six directions, by considering the prostate as a rigid, non-rotating volume. By doing so, we were able to directly compare the delineations done by the physicians on daily CBCT images with the initial delineation done on the CT-sim and MRI, and sort them by direction using the polar coordinates of the points. The computed variabilities were then used to compute a PTV margin based on Van Herk margin recipe. The total margin computed with random and systematic delineation uncertainties was of 2.7, 2.4, 5.6, 4.8, 4.9 and 3.6 mm in the left, right, anterior, posterior, cranial and caudal directions, respectively. According to our results, the gain offered by the separation of the delineation uncertainty into systematic and random contributions due to the adaptive delineation process justifies a reduction of the PTV margin down to 3 to 5 mm in every direction.