Basic investigation on performance of low-density polymer gel dosimeter

Background: in this study a series of basic dosimetric properties of a low-density [LD] gel dosimeter are investigated. The dose response is studied regarding to linearity, sensitivity, dose-rate and energy dependence as well as lung tissue equivalence

Materials and Methods: the LD gel was made by mixing the polymer gel with expanded polystyrene spheres. Energy dependence was studied at two different energies: 1.25 MeV and 6 MV photon beams which were produced by [60]Co and Linac machines. Investigation of dose rate dependence was performed in the low, medium, and high absorbed dose regions. Also reproducibility of dose response was studied in three sets of LD gel with identical preparation, irradiation and imaging procedure at three different days. Moreover the linearity and sensitivity were investigated up to 30Gy

Results: the results showed that the dose response was reproducible. The gel response was found linear up to 22Gy with r[2]=0.981 and sensitivity of 0.814S[-1]Gy[-1]. In the measured ranges, the dose response of LD gel was independent of beam energy within less than +/-0.02 and dose rate had no effect on the gel response. LD gel was nearly lung tissue equivalent with mass density 0.37 to 0.4g/cm3 and relative electron density 0.41

Conclusion: MAGAT LD gel dosimeter appears to be a promising dosimeter in all aspects of dosimetric properties evaluated in this study. In addition, its high linearity together with no dose rate dependence in different level of absorbed doses makes it a suitable dosimeter to measure 3D-dose distributions inside a non-homogeneous media

Three-dimensional gel dosimetry for dose volume histogram verification in compensator-based IMRT

Some tissues in human body are radiobiologically different from water and these inhomogeneity must be considered in dose calculation in order to achieve an accurate dose delivery. Dose verification in complex radiation therapy techniques, such as intensity-modulated radiation therapy [IMRT] calls for volumetric, tissue equivalent and energy independent dosimeter. The purpose of this study is to verify a compensator-based IMRT plan in anthropomorphic inhomogeneous phantom by Dose Volume Histograms [DVH] using polymer gel dosimetry. An anthropomorphic pelvic phantom was constructed with places for gel inserts. Two attached cubic inserts for prostate and bladder and a cylindrical insert for rectum. A prostate treatment case was simulated in the phantom and the treatment was delivered by a five field compensator-based IMRT. Gel dosimeters were scanned by a 1.5 Tesla magnetic resonance imaging [MRI]. Results were analyzed by DVH and difference of differential DVH. Results showed for 3D compensator-based IMRT treatment plan for prostate cancer, there was overall good agreement between calculated dose distributions and the corresponding gel measured especially in planning target volume [PTV] region. Our measurements showed that the used treatment plan configuration has had clinically acceptable accuracy and gel dosimetry can be considered as a useful tool for measuring DVH. It may also be used for quality assurance and compensator-based IMRT treatment verification

Patient effective dose evaluation for chest x-ray examination in three digital radiography centers

The radiation doses resulting from diagnostic X-ray examinations are routinely measured in terms of entrance surface dose [ESD] and effective dose [ED]. In this study, for the purpose of radiation protection, the radiation doses received from Digital chest X-ray examination were evaluated in terms of ESD and ED. The ED was calculated by using the MCNP Monte Carlo code and an adult hermaphrodite mathematical phantom. The effects of both operating high voltage and projection geometry on the effective dose were investigated. The absolute values of the ED were calculated for digital and conventional Posterior-Anterior [PA] and Lateral [LAT] projections of chest radiography. The results show ED for PA projection in digital chest radiography in some major hospitals is higher than National Diagnostic Reference Level [NDRL]. Therefore optimization process should be considered seriously at national level to reduce patient exposure in digital chest radiography in Iran

[Agreement of two methods of planar and SPECT scintigraphy with 99mTc- RBC in detection of liver Hemangioma]

Hemangiomas are the most frequent benign tumors of the liver and detecting them from metastasis or other malignant hepatic tumors is of outmost importance. 99mTc- RBC scan is highly specific and is the method of choice for this differentiation. This scintigraphy is performed in Planar and SPECT modes. These two procedures are in agreement most of the times, however since SPECT is more expensive and time consuming we planned a study to evaluate the agreement of these two methods. Sixty two patients [age range 20-80 yr, mean age 42 yr], 41 female [67%] and 20 male [33%], who were under evaluation for liver mass detected on abdominal ultrasound or CT scan, underwent 99mTc- RBC scan with both Planar and SPECT methods. The data was processed by computer and SPSS software [11.5]. Planar scan was positive in 42% and negative in 59% of cases, while for SPECT study these values were 68.9% and 31.1%, respectively. The Kappa value for planar and SPECT scan results was 48%, and there were 17 lesions [27%] which were detected only by SPECT. SPECT scan defined 35% of the posteriorly located hemangiomas, and 58.3% of hemangiomas smaller than 3 cm, which were not detected by planar scans. Also 75% of patients with multiple hepatic lesions showed more lesions by SPECT as compared to planar scan. Since there is a weak agreement between SPECT and Planar scan, SPECT is considered the more reliable method in diagnosis of liver hemangioma and this is especially true when the hemangioma is of small size, has a posterior location or in cases of multiple lesions

[Radioiodine treatment effect on lacrimal glands function in patients with thyroid cancer]

There is a limited number of case reports published in the past decade confirming the radio-iodine presence in the tear. These observations as well as reported cases of salivary and lacrimal gland dysfunction after radioiodine therapy stimulated investigators to clarify whether lacrimal gland function can be affected post-radioiodine therapy. Hence we planned a historical cohort study to evaluate this effect. We studied 100 eyes of 50 patients who were referred to the nuclear medicine department of Dr. Shariati hospital from 01.1383 to 02.1384 and had received high doses [accumulative dose: 100-450mCi] of I-131 treatment of differentiated thyroid carcinoma with their latest admission at least 3 months previously. Dry eye symptoms [obtained via a standard questionnaire] and Schirmer I test results [mm/5min] of this group were compared with those of an unexposed group [100 eyes of 50 individuals] matched by sex and age. Cases with another known cause[s] of dry eye were not included in either group. 51% of the exposed eyes and 50% of the unexposed ones revealed at least one of the dry eye symptoms in the questionnaire. Data analysis showed no significant difference between the number of symptoms of two groups, but 2 symptoms [burning, unrelated to light and erythema] were significantly higher in the exposed eyes. From 9 exposed eyes complaining of erythema, Schirmer test result was abnormal only in 2 [one patient]. Also among the 10 eyes with burning symptom [unrelated to light] one patient [2 eyes] revealed abnormal Schirmer test result. The study also demonstrated a significantly lower wetting amount of the Schirmer paper in exposed group compared to others. In the patients undergone radio-iodine therapy, results were 0-4 mm in 21%, 5-9 mm in 20% and 10 mm or more in 59%. These results were seen in the unexposed group in 6%, 17% and 77%, respectively. File review of the 21 exposed eyes with 0-4 mm Schirmer test results revealed presence of the migraine history in five [4 woman] surprisingly and 131I-avid skull metastasis in another patient [2 eyes]. Long-term reduction in the tear secretion from major and/or minor lacrimal glands is seen after high-dose radio-iodine therapy, which seems to be severe in the majority of patients; however these patients complain of dry eye symptoms no more than unexposed population. Conditions such as migraine may be unknown causes of impaired tear secretion and need further investigation

Determination of optimum filter in myocardial SPECT: a phantom study

In myocardial perfusion SPECT imaging, images are degraded by photon attenuation, the distance-dependent collimator, detector response and photons scatter. Filters greatly affect quality of nuclear medicine images Materials and A phantom simulating heart left ventricle was built. About 1mCi of 99mTc was injected into the phantom. Images were taken from this phantom. Some filters including Parzen, Hamming, Hanning, Butterworth and Gaussian were exerted on the phantom images. By defining some criteria such as contrast, signal to noise ratio, and defect size detectability, the best filter can be determined. 0.325 Nyquist frequency and 0.5 Nq was obtained as the optimum cut off frequencies respectively for hamming and hanning filters. Order 11,cut off 0.45 Nq and order 20 cut off 0.5 Nq obtained optimum respectively for Butterworth and Gaussian filters. The optimum member of every filter's family was obtained

value of myocardial perfusion imaging in differentiating between idiopathic dilated cardiomyopathy from the ischemic form

Differentiating between ischemic cardiomyopathy [ICM] and idiopathic dilated cardiomyopathy [IDCM] is important as coronary revascularization can improve prognosis in the ischemic subgroup. Due to inherent problems of coronary angiography in patients with depressed ejection fraction [EF] introducing a noninvasive tool to diagnose those who will benefit from angiography seems to be rewarding. We examined usefulness of myocardial perfusion scan in this group of patients. Study was performed on 64 patients [62 male and 2 female] aged 57.1 +/- 6.7y [mean +/- SD] all with dilation of the left ventricular [LV] cavity and ejection fraction less than 40% by echocardiography. Myocardial perfusion scan was performed in stress and rest phases. All the patients had coronary angiography which was used as the gold standard test. On each set of images, heart was arbitrary divided into 17 segments and perfusion abnormality in each segment was scored by a 5 grade scoring system [0-4]. Summed Stress Score was used as the scan criteria to differentiate dilated ischemic from idiopathic cardiomyopathy. Scores more than 17 were considered ischemic, and less than that, idiopathic. Results were compared with angiography. From total 40 cases of ischemic cardiomyopathy [proved by angiography] 39 were correctly diagnosed by scan and only one case was miscategorized as IDCM. All 24 cases of IDCM were correctly diagnosed by scintigraphy. Sensitivity, specificity, positive predictive value, and negative predictive value of myocardial perfusion imaging for discrimination between ischemic and idiopathic dilated cardiomyopathy were 97.5%, 100%, 100%, and 96% respectively. Considering excellent accuracy of myocardial perfusion scan with scoring system in discrimination of ischemic dilated cardiomyopathy from idiopathic dilated cardiomyopathy, this noninvasive test could be considered the main diagnostic test

Evaluation of performance quality of SPECT camera in sharyati hospital of Tehran university of medical sciences

In nuclear medicine, there are two methods of imaging, planar and tomography. Single photon emission computerized tomography [SPECT] shows better image details and therefore is influenced more by image parameters such as resolution, uniformity, sensitivity, etc. Manufacturers provide customers with data which are obtained by complicated and sometimes secret methods. Marketing companies test and verify these data and buyers perform acceptance testing on installation of system. Since acceptance testing is not usually done in our country, follow up of system performance and therefore setting up of a comperehensive quality control program faces difficulty. In this research which was done sometimes after installation, evaluation of SPECT system was carried out and data obtained were compared with those of manufacturer catalogue. It was found that in most cases our figures do not correspond to those of manufacturer catalogue, therefore acceptance testing using standard and precision devices being carried out by trained personnel is strongly recommended