Quantitative SPECT and planar 32P bremsstrahlung imaging for dosimetry purpose - an experimental phantom study

In this study, Quantitative 32P bremsstrahlung planar and SPECT imaging and consequent dose assessment were carried out as a comprehensive phantom study to define an appropriate method for accurate Dosimetry in clinical practice. CT, planar and SPECT bremsstrahlung images of Jaszczak phantom containing a known activity of 32P were acquired. In addition, Phantom contour was determined for attenuation correction and image registration. Reconstructed SPECT slices were corrected for attenuation effect using two different methods: conventional Chang's method and an expectation maximization algorithm followed by CT and SPECT image registration. Cumulated activity was calculated by a predefined calibration factor. Both attenuation correction algorithms were quantitatively assessed by the Monte Carlo SIMIND program. Acquired planar Bremsstrahlung images were quantified by the Conjugate View Method, as well. Calculated activities were statistically different among various quantification methods [P= 0.0001]. When iterative expectation maximization algorithm and applied methods were used, mean calculated activity had the least difference with real activity of +/- 3%. Quantitative 32P Bremsstrahlung SPECT imaging could accurately determine administered activity and assess radiation dose if precise attenuation correction and appropriate registration with CT were done even without sophisticated scatter correction or when SPECT/CT machines are not available. Therefore, it has the potential of specific tumor/organ dosimetry in clinical practice. The best method for calculating activity is quantitative SPECT using iterative expectation maximization algorithm. Additionally, applied method for determining phantom contour was practical for attenuation correction and image registration

SPIO-Annexin V, a potential probe for MRI detection of radiation induced apoptosis

Finding a suitable method for rapid, accurate and reliable estimation of absorbed dose has high priority in management of the radiation exposed persons. Shortly after radiation exposure, apoptosis is a major detriment in proliferative tissues such as the hematopoietic system. Therefore, quantification of apoptosis in these tissues could be useful for rapid estimation of radiation exposure. Annexin V [ANX] is considered as a biological probe for detection of apoptotic cells. The aim of the present study is to investigate the potential suitability of apoptosis quantification for estimation of radiation exposure. In order to determine the biological distribution of ANX within the mice body after radiation exposure, mice whole body irradiated with 2, 4, 6 and 8 Gy [60Co gamma rays]. Ten hours later, ANX conjugated with super paramagnetic iron oxide nanoparticles [SPIO-ANX] was administered intravenously and magnetic resonance imaging was conducted 3 hours later. Average signal intensities in the regions of interest [ROIs] of the femur bone marrow, liver and testis were calculated and normalized to parafemoral muscle signals. SPIO-ANX accumulated in bone marrow of irradiated groups and significantly decreased the normalized mean of signal intensity for bone marrow in comparison with control group [p< 0.01]. Tracing and quantification of SPIO-ANX in bone marrow can be used as an indicator for radiation exposure. However, development and optimization of the assay are necessary for discrimination between different radiation doses

Individual virtual phantom reconstruction for organ dosimetry based on standard available phantoms

In nuclear medicine application often it is required to use computational methods for evaluation of organ absorbed dose. Monte Carlo simulation and phantoms have been used in many works before. The shape, size and volume in organs are varied, and this variation will produce error in dose calculation if no correction is applied. A computational framework for constructing individual phantom for dosimetry was performed on five liver CT scan data sets of Japanese normal individuals. The Zubal phantom was used as an original phantom to be adjusted by each individual data set. This registration was done by Spherical Harmonics [SH] and Thin-Plate Spline methods. Hausdorff distance was calculated for each case. Result of Hausdorff distance for five individual phantoms showed that before registration ranged from 140.9 to 192.1, and after registration it changed to 52.5 to 76.7. This was caused by index similarity ranged from%56.4 to%70.3. A new and automatic three-dimensional [3D] phantom construction approach was suggested for individual internal dosimetry simulation via Spherical Harmonics [SH] and Thin-Plate Spline methods. The results showed that the individual comparable phantom can be calculated with acceptable accuracy using geometric registration. This method could be used for race-specific statistical phantom modeling with major application in nuclear medicine for absorbed dose calculation

Chorionic villus sampling and marked membrane separation

The major concern about the invasive prenatal diagnostic tests is the frequency of procedure induced pregnancy loss. Chorionic Villus Sampling [CVS] is the invasive test of choice in the first trimester after the 10th gestational week. Our experience suggests marked chorioamniotic separation is an uncommon finding after the 10th gestational week. This study assesses the rate of marked membrane separation in a 10 to 14-week gestational period and its effect on post CVS fetal loss. Forty-one patients [5.2%] were selected among 782 patients as cases with marked membrane separation [mean maternal age, 26.9 years]. CVS procedures were performed with a 20-gauge Chiba needle attached to a 20-ml syringe under ultrasound guidance. Follow-up was performed by phone call and clinical visits until 24 weeks of gestation. For the control group, the follow-up was performed for only 2 weeks. Early fetal loss in the first two weeks of post procedural period, and late fetal loss from 2 weeks after procedure till the 24th gestational week were considered as CVS complications. We detected 2.4% early fetal losses after the procedure. Fourteen cases voluntarily underwent therapeutic abortion due to beta-thalassemia or hemophilia. One fetus with microcephaly was spontaneously aborted in the 21st gestational week. Twenty-five neonates were delivered alive at term and one prematurely at the 32nd week. Marked membrane separation had no significant effect on early post CVS fetal loss rate. The procedure does not have a major impact on the early post CVS fetal loss in patients with marked membrane separation

new approach to contrast enhancement in MAGICA gel dosimeter image with MRI technique

Sensitivity and resolution are two main parameters that have to be measured in gel dosimetry. However, the resolution in gel is strongly dependant on gel composition. Selection of optimum method in dose response readout and proper values of parameters can result in noise reduction as well as improvement of contrast, and spatial resolution considerably. MAGICA polymer gel dosimeters were manufactured and irradiated to different doses using a 60Co therapy unit. Imaging was performed in a 0.5T MRI with 8 echoes in air and water as a hydrogenous environment. Imaging condition was kept constant, as much as possible, in both imaging modalities. Images obtained from these two procedures were compared quantitatively. R2- dose curves have three different sections, sensitivity obtained in these three sections were 1.039, 1.671, 1.260 Gy[-1]S[-1] and 1.032, 1.729, 1.37 Gy[-1]S[-1] for water and air respectively. Calibration errors were investigated and graphically were compared in two different methods. Imaging in water medium for doses lower than 17 Gy led to a small reduction in spatial resolution was exchanged to a considerable increase of contrast in R2 map. For doses higher than17 Gy, imaging in water or air was preferred depending on the importance of contrast or spatial resolution

Radiofrequency ablation of liver tumors: the first preliminary reported in Iran

Radiofrequency ablation [RFA] is emerging as a new therapeutic technique for unresectable hepatic malignancies. We report our experience with the use of this method for the first time in Iran. Eighteen patients with primary or metastatic hepatic malignancies, which were considered not suitable for surgical resection, were included in our study. RFA was performed via the percutaneous ultrasound'guided method, under general anesthesia, by an interventional radiologist. Patients were followed prospectively with contrast-enhanced CT or ultrasonography, and tumor marker serum levels 1, 3 and 6 months after RFA. RFA was used to treat 26 tumors [diameters of 12-70 mm]. These tumors included hepatocellular carcinoma in three cases and metastatic carcinoma in 23 cases. Three patients had complications: two bilomas and one abscess in the right lobe. At follow-ups, tumor recurred at the site of RFA in four tumors, all of which were over 4 cm in diameter. RFA is a procedure with the potential to be safe and effective for treating unresectable liver tumors

Effect of famotidine on radiation induced apoptosis in human peripheral blood leukocytes

Radioprotective effects of famotidine, an antagonist of H2 receptor clinically used for peptic ulcer treatment, was previously shown on radiation-induced micronuclei and chromosomal aberration in human peripheral blood lymphocytes and mouse bone marrow cells. This study was conducted to investigate radioprotective property of famotidine against radiation induced apoptosis in human peripheral blood leukocytes. Peripheral blood was obtained from 6 healthy volunteers including three males and three females. 12 microL of blood sample diluted in 1 ml RPMI-1640 supplemented with antibiotics and foetal calf serum was irradiated a dose of 8 Gy gamma rays generated from a Co-60 source at a dose rate of 1.27 Gy/min. After 48 h incubation in a 37 ?C incubator, cells embedded in low melting point agarose were transferred to a slide precoated with normal agarose. Cells were lysed and subjected to electrophoresis under neutral condition. Slides were then stained with ethidium bromide and analysed under a fluorescence microscope. 500 cells were analysed for each sample for the presence of apoptosis. The data were statistically evaluated using Man-Whitney non-parametric and ANOVA tests. Results show a significant increase in apoptosis induction following 8 Gy gamma-irradiation comparing with controls [p<0.001]. The presence of famotidine at 50 and 100 microg/ml did not show any protective effect against radiation induced apoptosis; however, the presence of famotidine at higher concentration [200 microg/ml] significantly deceased radiation induced apoptosis [p<0.001]. The obtained results suggest that famotidine suppresses radiation-induced apoptosis at 200 microg/ml, probably via OH radical scavenging and an intracellular antioxidation mechanism. Famotidine appears to be a useful candidate for the future development of post-irradiation radioprotectors

Brachytherapy polymer gel dosimetry with xCT

Polymer gels are an emerging new class of dosimeters which are being applied to the challenges of modern radiotherapy modalities. Research on gel dosimetry involves several scientific domains, one of which is the imaging techniques with which dose data is extracted from the dosimeters. In the current work, we present our preliminary results of investigating capability of X-ray CT for extracting brachytherapy dose distributions from a normoxic gel dosimeter. A normoxic radiosensitive polymer gel was fabricated under normal atmospheric conditions and poured into three phantoms. Using Cs137 brachytherapy sources, the phantoms were irradiated with different dose distributions with a LDR Selectron remote after-loader. To improve SNR, 25 images were obtained of each slice for image averaging and an averaged background image of an un-irradiated gel phantom was then subtracted for artifact removal. To further improve the accuracy, a self-consistent normalized method was used for calibration of the dosimeters based on an assumption of a linear dose response between zero and maximum dose regions in the gel. Although results reveal very similar CT-number gradients to that of brachytherapy dose distributions, but the method does not fulfill brachytherapy dosimetry requirements. This might be due to the high prescribed doses in this study which in turn results in a large change in the CT numbers. This change in the CT numbers of the images can not be considered to have a linear relationship with dose which was the basic assumption of our calibration method, so the results are just qualitatively comparable. In this study, the results of using X-ray CT for brachytherapy polymer gel dosimetry is promising but not still satisfying. Improving a proper calibration method for correlating CT numbers to dose will be significantly helpful for performing measurements with CT. The main limitation for CT is still a low signal to noise ratio especially in lower dose areas

3D MRI gel dosimetry bases on image intensity: a new approach

Since 1984 MRI gel dosimetry has been introduced as a potential technique for 3D dosimetry. Most of the studies have measured R1 [1/T1] or R2 [1/T2] properties of the gel depending on the gel type. We have studied image intensity change in the Fricke gel by different MRI protocols. Materials and Gel Dosimeters contain 0.4 mM ferrous sulphate, 1 mM NaCl, 50 mM H2SO4 and 1% by weight agarose in distilled water. Prepared gels were poured in Plastic tube phantom and irradiated to a beam of Co-60 gamma rays. Imaging was performed by a 0.5T MRI system in the head coil with SE and GRE techniques. Our results showed that linear response exists between the variations of image intensity with absorbed dose [1-15 Gy]. Optimal imaging parameters should be defined locally according to the type of MRI scanner and exact composition of the gel. Gradient echo [GRE] imaging technique also have been studied in comparison with classic spin echo [SE] imaging technique which will be discussed in detail. Conclusions: Linearity of absorbed dose with intensity exists up to 15 Gy and can be used for MRI gel dosimetry. Reduction of imaging time is achievable in image intensity technique so that it's possible to image the gel in less than 20 minutes, which is critical to over-come the adverse ion-diffusion properties of the Fricke gel

Dental tissue as a TLD dosimeter

Thermoluminescence dosimetry is one of the dosimetry procedures used widely as routine and personal dosimeters. In order to extend this kind of dosimeters, dental tissue has been examined and was found promising as a TLD dosimeter. Materials and In this study, 70 health teeth were collected. The only criterion, which was considered for selection of the teeth, was the healthiness of them regardless of age and gender of the donors. All collected samples were washed and cleaned and milled uniformly. The final powder had a uniform grain size between 100 - 300 micrometer. The sample was divided into four groups. Group A and B were used for measurement of density and investigation of variation of thermoluminescent characteristics with temperature respectively. Groups C and D were used for investigation of variation of thermoluminescent intensity with dose and fading of this intensity with time. In all cases the results obtained with dental tissue were compared to a standard LiF, TLD dosimeter. It was found that, average density of the dental tissue was 1.570 g/cm3, which is comparable to density of LiF, which is 1.612 g/cm3. It was also concluded that the range of 0-300°C, dental tissue has a simple curve with two specific peaks at 140 and 250°C respectively. The experiment also showed that, the variation of relative intensity versus dose is linear in the range of 0.04 - 0.1Gy. The fading rate of dental tissue is higher than LiF but still in the acceptable range [14% per month in compare to 5.2% per month] Dental tissue as a natural dosimeter is comparable with TLD and can be used in accidental events with a good approximation