فهرست مطالب k khoshgard

Concern about radiation risk of computed tomography (CT) scan as a diagnostic modality has increased in recent years. Diagnostic reference levels (DRLs) is one of the tools to optimizing radiation dose of patients. CTDIv (Volume Computed tomography dose index) and DLP (Dose Length product) are used for assessment of DRLs. The CTDIv under/overestimate the patient dose. AAPM has introduced SSDE (Size-specific dose estimates) for estimation of patient. In this study, the DRLs of head and abdomen-pelvis CT examinations of adults is determined using CTDIv, DLP and SSDE.

680 CT examinations of head and abdomen-pelvis were collected from PACS (Picture archiving and communication system) in Imam Khomeini and Mostafa Khomeini hospitals. The Deff, CF and SSDE calculated using AAPM TG-204 and TG-220. Statistics analysis calculated using SPSS version 18.

For abdomen-pelvis third quartile of CTDIV, SSDE and DLP was 9.96, 13.58 and 527 and values of 27.62, 26.79 and 402.90 are determined for head, respectively that are lower than national DRLs. Also, calculated conversion factor (CF) for head and abdomen-pelvis was 0.97 ± 0.75and 1.45 ± 0.17, respectively.

DRLs were lower than other studies in this study. Using the AEC (Auto Exposure Control) and different kVp in this hospitals can help optimization of patient dose. The SSDE must be calculable by radiographers to more accurate estimation of patient dose using CFs.

Head and neck cancers are currently the most common types of cancers. 3D-conformal radiation therapy is the most common dose delivery technique for head and neck cancers. Eye Lens is a radio sensitive structure and cataract formation as a visual disorder associated with exposure to ionizing radiation which is documented.

Determining the radiation dose to eye lens during head and neck radiography and estimating the probability of cataract induction are essential.

This experimental study was performed on 14 patients with head and neck cancers through experimental study analysis. The maximum opacity of the eyes lens were measured by pentacamTM before radiation therapy. CT data of patients were transmitted to Isogray treatment planning Software, and dose calculations for each patient was performed. At the end of radiation treatment, 3 and 6 months after radiotherapy, the eye lens opacity of the patients was assessed.

Overall, 28 lenses were studied. Statistical one sample K- S test proved normality of obtained data. Using repeated measures test, the relation before and 3 months after radiotherapy, as well as the relationship before and 6 months after radiotherapy proved a significant relationship.

The opacity caused by radiation in eyes is a non-statistical and linear-quadratic response curve with no threshold. This opacity can also appear within 3 months after completion of radiation therapy.

131I source is widely used in the treatment of hyperthyroidism and thyroid cancers. 131I emits both beta and gamma-rays. Radiation protection is considered for gamma rays emitted by 131I. It seems no special shield against 131I source to be designed. This research aims to evaluate determination of optimum shields in nuclear medicine against 99Tcm and 131I sources by dosimetric method. Additionally, Monte Carlo simulation was used to find the optimum thickness of lead for protection against 131I source. This is an experimental research in the field of radiation protection. A calibrated model of GraetzX5C Plus dosimeter was used to measure exposure rates passing through the shields. The efficiency of the shields was evaluated against 99Tcm and 131I. Furthermore, Monte Carlo simulation was used to find the optimum thickness of lead for protection against 131I source. The findings of the dosimetric method show that the minimum and maximum efficiencies obtained by the lead apron with lead equivalent thickness of 0.25 mm and the syringe holder shields with thickness of 0.5 mm lead were 50.86% and 99.50%, respectively. The results of the simulations show that the minimum and maximum efficiencies obtained by lead thicknesses of 1 mm and 43 mm were 19.36% and 99.79%, respectively. The optimum shields against 99Tcm are the syringe holder shield, the tungsten syringe shield, and the lead partition, respectively. Furthermore, based on simulations, the thicknesses of 11-28 mm of lead with efficiencies between 90.6% to 99% are suggested as the optimum thicknesses to protect against 131I source.

Recent dvances in nanotechnology have enabled us to accumulate high atomic-number nano-materials, such as gold nanoparticles (GNPs), in tumor cells selectively using different techniques and take the advantage of the dose enhancement factor resulting from the presence of such high-Z elements as the vicinity of cancerous cells as a radiosensitizer agent. In this research, the GNPs with an average diameter of 50nm were synthesized and conjugated with folic acid. Different concentrations of this nanoconjugate were incubated with MCF-7 cells for 24 hours and its cytotoxicity was investigated. The results showed that increasing the nanoconjugate concentration up to a critical amount, affects the cells viability. The radiosensitizing effect of the folate nanoconjugate, with a concentration of 50μg/mL, on the MCF-7 cells was assessed under 2Gy of x-ray radiation, generated by an orthhovoltage radiotherapy machine, at various energies of 120, 180, 200 kVp, using the MTT assay. Significant differences in the cell survival were noted among the groups exposed to x-ray radiation with and without the nanoconjugate. A maximum dose enhancement factor of 1.34±0.03 was obtained for the 180kVp X-ray beam. The findings enable us to decrease by one third of the prescribed dose while having the same level of damage to cancer cells. Also, this dose reduction results in lower exposure to the normal tissues located close to the target.