International Journal of Radiation Research
Volume:4 Issue: 1, Jan 2006

In order to assign appropriate planning target volume (PTV) margins, each centre should measure the patient positioning deviations for their set-up techniques. At the Royal Marsden Hospital, UK, a conformal shell (cast) system is used when a stereotactic frame is not suitable. In this paper, we report on a series of measurements with the aim of obtaining the systematic and random components of positioning error when using the above-mentioned shell system. The verification protocol was based on orthogonal pairs of anterior-posterior and lateral electronic portal images (EPIs) used to check the isocentre position. The isocentre verification results of paediatric patients were analysed. A practical ‘off-line’ patient set-up correction strategy had been used with the aim of reducing systematic errors. The verification protocol involved EPI acquisition on the first three fractions and then on a weekly basis. Additional images were taken if an isocentre movement was applied based on a 3 mm tolerance for a consistent 1D discrepancy. Four patients required isocentre corrections ranging between 2 mm and 4 mm. Following the off-line corrections, the residual systematic errors in each direction were within 0.5 mm while the 1D random variation was about 1.0 mm. The head fixation system in conjunction with the correction strategy successfully kept the random and systematic positioning errors within an acceptable level well within the 3 mm tolerance. The measured components of positioning error can be used to define appropriate PTV margins.

There is not any report on the radiation doses received by patients in diagnostic radiology sections in hospitals under control of Chaharmahal and Bakhtiari Medical Sciences University, in the south west of Iran. The aim of this study is measurement of entrance surface doses (ESD) for the most routine types of X-ray procedures in radiology centers as part of ongoing dose reduction program. Geiger-Muller and thermoluminescence dosimeters (TLD), were used to measure entrance surface doses for four common radiographic views in six hospitals (7 X-ray machines). The entrance surface dose was measured on 20 randomly selected patients (male and female) for each X-ray examination. Patients were not exposed to any additional radiation and the radiographs were used for diagnostic purposes. The entrance surface doses for the PA and lateral chest X-ray examinations were found to be in the range of 0.22-1.45 and 0.34-4.90 mGy, respectively. The ESD values for the AP or PA skull and LAT skull were in the rage of 2.55-8.45 and 2.85-9.12 mGy, respectively. Most of the ESD measured doses were slightly greater than the ICRP and NRPB reference doses. The results of the present study indicate a need for quality assurance (QA) programs to be undertaken to avert considerable cost and high patient doses. The recommendations to avoid unnecessary radiation exposure are also given without lose of image quality.

Monte Carlo (MC) modeling of a linear accelerator is a prerequisite for Monte Carlo dose calculations in external beam radiotherapy. In this study, a simple and efficient model was developed for Elekta SL-25 linear accelerator using MCNP4C Monte Carlo code The head of Elekta SL-25 linac was simulated for 6 and 18 MV photon beams using MCNP4C MC code. Energy spectra and fluence distribution of photons crossing the phase space plane were calculated. A simple point source model was developed based on calculated photon spectra and spatial distribution. Using this model, percent depth doses (PDDs) and beam profiles were calculated for different field sizes. The results of MC calculations were compared with measurements. There was a good agreement between MC calculations and measurement for descending part of PDD curves. But, comparing calculated PDDs with measurement showed up to 10% differences for build up region of PDD curves for both energies. For beam profiles, there was 2% difference in flat region and up to 15% difference was seen for out of field region. These results were acceptable according to recommended criteria. Although, using our model the run time was decreased 24 times in comparison to original full Monte Carlo method. Our study showed that our model is accurate and effective for MC calculations in radiotherapy treatment planning. Also, it substantially lowers MC runtime for radiotherapy purposes.

Palladium-103 (103Pd) is a brachytherapy source for cancer treatment. The Monte Carlo codes are usually applied for dose distribution and effect of shieldings. Monte Carlo calculation of dose distribution in water phantom due to a MED3633 103Pd source is presented in this work. The dose distribution around the 103Pd Model MED3633 located in the center of 30×30×30 cm3 water phantom cube was calculated using MCNP code by the Monte Carlo method. The percentage depth dose (PDD) variation along the different axis parallel and perpendicular to the source was also calculated. Then, the isodose curves for 100%, 75%, 50% and 25% PDD and dosimetry parameters of TG-43 protocol were determined. The results show that the Monte Carlo Method could calculate dose deposition in high gradient region, near the source, accurately. The isodose curves and dosimetric characteristics obtained for MED3633 103Pd source are in good agreement with published results. The isodose curves of the MED3633 103Pd source have been derived form dose calculation by MCNP code. The calculated dosimetry parameters for the source agree quite well with their Monte Carlo calculated and experimental measurement values.

Application of Dose-area product (DAP) quantity has been increased in the clinical practice. DAP is relatively easy to measure. DAP has been shown to correlate well with the total energy imparted to the patient, which is related to the effective dose. In this study, measurements of DAP were carried out in a sample of 421 adult patients who underwent conventional radiological examinations. Then, by using DAP some useful dosimetric quantities such as exposure area product (EAP), air kerma and entrance surface dose (ESD) were estimated. Furthermore, ESD was calculated by a Multi-O-Meter dosemeter. Effective doses were computed by measurement of DAP and corresponding conversion factors. Finally, the effective dose was determined using: i) ESD and data published by NRPB. ii) energy imparted derived from DAP, and iii) ODS-60 package. The effective dose values derived from the four methods are in good agreement. The mean effective dose estimated from DAP measurement were 0.13, 0.42, 0.05, 0.59, 0.54 and 0.03 mSv/projection for chest, abdomen, cervical spine, lumbar spine, pelvis and skull examinations, respectively. Indirect effective dose determination using the NRPB dosimetric data and the measured value of DAP or ESD allows for reliable estimates of effective dose. The ODS-60 software was used in this study because it has the flexibility to manipulate the technical parameters of an examination and patient''s parameters.

There is not any report on the radiation doses received by patients in diagnostic radiology sections in hospitals under control of Chaharmahal and Bakhtiari Medical Sciences University, in the south west of Iran. The aim of this study is measurement of entrance surface doses (ESD) for the most routine types of X-ray procedures in radiology centers as part of ongoing dose reduction program. Geiger-Muller and thermoluminescence dosimeters (TLD), were used to measure entrance surface doses for four common radiographic views in six hospitals (7 X-ray machines). The entrance surface dose was measured on 20 randomly selected patients (male and female) for each X-ray examination. Patients were not exposed to any additional radiation and the radiographs were used for diagnostic purposes. The entrance surface doses for the PA and lateral chest X-ray examinations were found to be in the range of 0.22-1.45 and 0.34-4.90 mGy, respectively. The ESD values for the AP or PA skull and LAT skull were in the rage of 2.55-8.45 and 2.85-9.12 mGy, respectively. Most of the ESD measured doses were slightly greater than the ICRP and NRPB reference doses. The results of the present study indicate a need for quality assurance (QA) programs to be undertaken to avert considerable cost and high patient doses. The recommendations to avoid unnecessary radiation exposure are also given without lose of image quality.

The present study has been carried out to investigate the effects of preovulatory stage gamma-irradiation of female mice in the absence or presence of vitamin E on numerical chromosome abnormalities in 8-cell embryos after mating with non-irradiated males. The 8-11 weeks adult female NMRI mice were whole body irradiated at preovulatory stage (post PMSG injection and about 12-18 hours before injecting HCG) with 4 Gy gamma-rays generated from a cobalt-60 source alone or in combination with 200 IU/kg vitamin E, intrapretoneally administered one hour prior to irradiation. Soon after HCG injection super ovulated irradiated females were mated with non-irradiated males. About 68-h post coitous (p.c), 8-cell embryos were flushed from the oviducts of pregnant mice and were fixed on slides using standard methods in order to screen for metaphase spreads and numerical chromosome abnormalities. In control embryos, 8% of metaphase plates were aneuploid, whereas in preovulatory stage irradiated female mice, about 50% of metaphase plates of embryos showed numerical chromosome aberrations (P<0.001). Administration of vitamin E one hour before the irradiation reduced chromosomal aberrations significantly (P=0.005). Results show that the effects of gamma-irradiation on preovulatory stage oocytes led to chromosomal abnormalities in subsequent embryos generated by these oocytes. Increase the frequency of numerical chromosome abnormalities -mostly aneuploidy- may be due to abnormal chromosomal non disjunctions during 2nd meiotic division. Reduction of the frequency of chromosome aberrations in the presence of vitamin E is probably due to antioxidant effects of this vitamin, and scavenging free radicals induced by gamma-rays in mice oocytes’ environment.

Due to interesting tumor imaging properties of bis-thiosemicarbazones, [103Pd]-di-acetyl-bis (N4-methylthiosemicarbazone) ([103Pd] ATSM2) was prepared according to the analogy of radio copper homologues. Palladium-103 (T1/2=16.96 d) was produced via the 103Rh (p,n) 103Pd nuclear reaction with proton energy 18 MeV. The final activity was eluted in form of Pd (NH4)2Cl2 in order to react with bis-thiosemicarbazones to yield [103Pd]-labeled compounds. Chemical purity of the final product was confirmed to be below the accepted limits by polarography. The labeled compound was purified by reverse phase column chromatography using C18 plus Sep-Pak. The partition co-efficient of the final complexes were determined. The initial physico-chemical properties of the labeled compounds were compared to those of their copper homologues. Radiochemical purity of more than 99% using RTLC was obtained (specific activity of about 12500-13000 Ci/mol). The stability of the tracer was checked in final product and human serum, at 37C up to 48h. The labeled compound prepared in this study is probably one of the few new 103pd-radiolabeled compounds which have a potential for future biological studies, regarding its suitable physicochemical stability.

Two of the important radionuclides which are entered to environment and human diet are radium-226 (226Ra) and cesium-137 (137Cs). It is clear that the methods for preparation of foods such as peeling, washing, cooking or frying can affect the dose which is received by human due the to consumption of foodstuffs. An experiment has been performed at the environmental monitoring section of NRPD, aiming to measure the transfer of 226Ra and 137Cs from the tea leaves to drinking part of tea. Tea samples were pulverized to obtain a homogenous matrix which was weighed and placed in 1000 cm3 Marinelli beaker. After making tea, the liquid tea and tea-discard were analyzed separately. Measurement of 226Ra and 137Cs was performed by gamma spectrometry system using a high purity germanium (HPGe) detector with 40 % relative efficiency. The detector was shielded by 10 cm lead an all sides with cadmium -copper as liners. It was found that the activity concentration transferred from tea leaves to drinking tea for 137Cs and 226Ra are less than 2% and 17% respectively. On the basis of these measurements it seems that no significant levels of radioactivity of 226Ra and 137Cs can be found in drinking part of tea. The low concentration of the mentioned radionuclides in drinking tea is mostly due to tea dust and can be removed by its washing before preparing tea.