Quality Control Status of Radiology Centers of Hospitals Associated with Mashhad University of Medical Sciences

Introduction Using ionization radiation for diagnostic and treatment fields has increased worldwide dramatically. This issue causes an increase in the absorbed and collective doses in society noticeably. With regard to two main principles in radiation protection, i.e., justification and optimization, it is necessary to have imaging process with minimum dose to patients and personnel. For achieving this, it is vital to perform quality control tests regularly. On this topic, many studies have been performed and reported worldwide  which  show necessities and meaningfulness of QC tests. Materials and Methods In this study, Unfors Mult-O-Meter model 303 is used for surveying accuracy of kVp and time, linearity of exposure with mAs, and reproducibility of exposure. Results According to recommendations of AAPM (2002) and ICRP 103, in this study, 27% of apparatuses in accuracy of kVp, 45% in accuracy of timer, and 30% in accuracy of reproducibility were out of accepted range. Conclusion In surveyed apparatuses, both ends of operating range have large errors in therefore it is recommended that these devices should not be used  in the mentioned regions. Performing strict quality control on all radioactive devices is one of the radiation protection priorities that should be done periodically .With regard to the results, repair, substitution or omition of  some devices are suggested

A Dosimetric Evaluation of Organs at Risk in Prostate Radiation Therapy using a MAGIC Gel Dosimeter

Introduction: Multiple fields and presence of heterogeneities create complex dose distributions that need three dimensional dosimetry. In this work, we investigated MR-based MAGIC gel dosimetry as a three-dimensional dosimetry technique to measure the delivered dose to bladder and rectum in prostate radiation therapy. Materials and Methods: A heterogeneous slab phantom including bones was made. Paired cubes in the phantom representing bladder and prostate and a cylindrical container representing rectum were filled with MAGIC gel and placed in the anthropomorphic pelvic phantom. The phantom was irradiated with four beams as planned using a treatment planning system (TPS). Magnetic resonance transverse relaxation rate images were acquired and turned into dose distribution maps using a calibration curve. This calibration curve was obtained by linear fitting to R2 values of 4 test tubes against their given known doses. Image processing and data analysis were performed in MATLAB7 software. The gel dosimeter was validated using an ionization chamber. Dose maps and dose volume histograms (DVHs) were compared with dose distributions and DVHs of the TPS. Results: Mean “distance-to-agreement” and mean “dose difference” were 2.98 mm and 6.2%, respectively, in the comparison of profiles obtained from ionization chamber and gel dosimetry. Mean relative difference of DVHs between gel dosimetry and TPS data were 3.04%, 10.4% and 11.7%, for prostate, bladder and rectum, respectively. Discussion and Conclusions: Gel dosimetry is a good method for three dimensional dosimetry although it has a low precision in high dose gradient regions. This method can be used for evaluation of complicated dose distribution accuracy in 3D conformal radiotherapy, especially in presence of heterogeneities