[Comparison of absorbed skin dose received by patients in cone beam computed tomography, spiral and conventional computed tomography scanning]

The evaluation of absorbed dose received by patients could give useful information for radiation risk estimation. This study was performed to compare the entrance skin dose received by patients in cone beam computed tomography [CBCT], conventional and spiral computed tomography [CT]. In this experimental study, 81 calibrated TLD chips were used. The TLD chips were placed on facial, thyroid and end of sternum skin surface in patients referred for CT of the paranasal sinuses [3 TLD chips for each area] to estimate the absorbed dose received by central part of radiation field, thyroid and out of field areas, respectively. The data were analyzed using one-way ANOVA and Tukey tests. The dose delivered to the center of irradiated field was about 0.79 +/- 0.09 mGy in CBCT technique compared with 16.31 +/- 3.71 and 18.84 +/- 4.12 mGy for spiral and conventional CT, respectively. The received dose by the out of field areas was about 54 percent of central area dose. There was statistical significant relationship between the imaging modalities and absorbed dose received by patients [P=0.016]. The least absorbed dose was for CBCT and the greatest dose was for conventional CT imaging technique. The dose delivered to central area of irradiated field in conventional and spiral CT imaging modalities was about 24 times greater than of that in CBCT. Also, the highest received dose was for central areas of radiated field and the lowest dose was for the out of field areas

Evaluation of dosimetric characteristics of a grid block fabricated for mega-voltage grid therapy purposes

In conventional radiation therapy, regarding normal tissue tolerance, the treatment of bulk tumors is one of the remaining challenges. Grid Radiation Therapy [GRT] is a technique to deliver high doses, approximately 15 - 20 Gy per fraction, to several small volumes located in a large radiation field. This can be performed using a grid block. The current work has concentrated on the dosimetric characteristics of a designed mega-voltage grid, used for a unique treatment modality. All measurements performed using a Neptune linear accelerator [9 MV photon beam]. A square 16 x 16 array grid block was designed and fabricated. Several dosimetric characteristics including: depth dose, Valley To Peak [VTP] ratio, and grid out-put factor were evaluated using a calibrated diode dosimeter for a range of radiation fields. The percent depth dose curves, measured in the presence of grid block, lie within those measured for the corresponding open field and a narrow beam. At the D[max], the VTP ratio was found to be within 17% - 28%, while these ranges between 23% - 35% at a depth of 10 cm. The grid out -put factor found to be 0.78 and it slightly decreases with increasing of radiation field size. The VTP ratio found to be dependent strongly on the grid design and manufacturing properties. However, other parameters such as radiation field size and the depth of measurement should also be addressed as important factors. The measured dosimetric characteristics of grid block indicate that the mega-voltage grid therapy can be applied as a possible clinical modality for palliative cases

[Evaluation of radiation dose received by operating room personnel during radiological procedures]

Utilization of ionizing radiation in some surgery operations [especially orthopedic operations] is inevitable. One of the main occupational hazards of physicians and other personnel could be radiation exposure risks. This study aimed to evaluate the exposure doses received by operating room personnel in such surgery operations. 30 personnel of operation room in university affiliated hospitals of Hamadan city [excluding physicians and nurses] were studied as they received radiation doses. 3 TLD [thermoluminescent dosimet ers] chips were fixed on the apron of each staff member. To estimate the high risk examinations, staff members also completed a questionnaire about the type and number of the radiological examinations that they had participated. Minimum and maximum level of doses received by the participants were between 0.24 and 0.56 mSv in a four month period. Therefore, amount of annual doses received by the personnel would be between 0.73 and 1.7 mSv, respectively [without reduction of background radiation]. As the accuracy of TL dosimeters is normally about 0.1 mSv; therefore, it can be claimed that the received doses by the personnel was very low and comparable with background radiation. The results indicated that the radiation doses received by operating room personnel were very low. They were less than maximum predicted doses reported by the International Commission of Radiation Protection. However, the use of dose recording systems for awareness about absorbed doses beyond permitted limits is necessary

Radiation protection principles observance in Iranian dental schools

In recent decades many guidelines has been conducted by radiation protection organizations about radiation protection in dentistry. This study aimed to evaluate the observance of these guidelines in educational clinics of all dental schools in Iran. In this cross-sectional study a self-administered questionnaire, based on National Radiation Protection Board [NRPB] and European Commission guidelines, was conducted. The radiology departments of all dental school [18 schools] were surveyed in this study. The questionnaire was consisted of 3 sections including intraoral radiography, extraoral radiography and implementation of quality control programs. In the case of the existence of radiation protection facilities [such as lead apron, thyroid shield and lead impacted walls] the use of high speed films and existence of automatic processor in dental schools, there was a proper condition. The main problem was related to lack of regular quality control and quality assurance programs. Digital radiography systems were employed in none of the schools and it was occasionally used for research purposes at some of them. This study has emphasized on the need for further consideration of radiation protection principles in dental schools, especially on the field of quality control and quality assurance programs