Vol 6 No 4 (2019)

Original Article(s)

  • XML | PDF | downloads: 215 | views: 310 | pages: 168-173

    Purpose: The aim of this study is to compare the accuracy of different algorithms in EclipseTM Treatment Planning System (TPS) using a heterogeneous phantom.
    Materials and Methods: The method is based on the International Atomic Energy Agency's TEC-DOC 1583 report. The chest phantom of CIRS, PTW30010 ionization chamber and an electrometer (PTW, Freiburg) were used for the measurements.
    Three ACUROSE XB (AXB), Analytical Anisotropic Algorithm (AAA) and Pencil Beam Convolution (PBC) dose calculation algorithms available in Eclipse TM TPS were considered in this study.
    Results: Based on the measurements, the maximum differences between calculated dose by TPS and measured dose in TEC-DOC 1583 tests were 2.5%, 8.6% and 16.1% for the AXB, AAA and PBC algorithms in heterogeneous media, respectively.
    Conclusion: The Acuros XB algorithm has superior accuracy to predict the dose distribution in the heterogeneous tissues such as lung compared to AAA and PBC algorithms.

  • XML | PDF | downloads: 160 | views: 245 | pages: 174-180

    Purpose: Radiation Therapy has a fundamental role in the treatment of cancer. Achieving Tumor Control Probability (TCP), while avoiding normal tissue complication is the goal of this treatment modality. The sensitivity of the thyroid gland to radiation increases the risk of developing secondary thyroid cancer and hypothyroidism.
    Materials and Methods: The average dose to the thyroid from head and neck irradiation was measured using in vivo dosimetry (Thermolumincsence Dosimetry). The Radiotherapy technique was given using 6 MV x-rays from an Elekta compact linear accelerator and conformal technique delivered 1.8 to 2.0 Gy over 5 sequential days per week.
    Results: The average absorbed dose to the thyroid from head and neck radiotherapy was 4.4% of the prescription dose and from whole brain radiotherapy was 0.7% of the prescription dose. Thyroid Stimulating Hormone (TSH) levels were determined in 30 patients before and after completion of radiation therapy. The average concentration of TSH increased from 0.88 +/- 0.55 (pre-radiotherapy) to 1.7 +/- 0.66 (post-radiotherapy), (p < 0.05).
    Conclusion: Thyroid absorbed dose was less than the threshold dose for patients who received radiotherapy to the head and neck based on thyroid function tests.

  • XML | PDF | downloads: 124 | views: 259 | pages: 181-186

    Purpose: Positron Emission Tomography (PET) imaging is a nuclear medicine imaging technique based on the recording of two photons as coincidence created by positron annihilation.
    Materials and Methods: PET coincidence events include true and unwanted coincidences (random, scattered, multiple coincidences). We modeled the Discovery 690 (D-690) PET scanner using the GATE simulation tool and estimated the effect of the diameter of the scattering medium out of the Axial Field of View (AFOV) on the random coincidence rates.
    Results: The validation results indicated that the average difference between simulated and measured data for sensitivity and scatter fraction tests are 5% and 3%, respectively. Moreover, the results revealed that the increasing diameter of the scattering medium out of the AFOV has a direct effect on the random coincidence rates within the Field of View (FOV).
    Conclusion: The study concluded that the presence of a scattering medium near the FOV increases the rate of random coincidences.

  • XML | PDF | downloads: 117 | views: 253 | pages: 187-196

    Introduction: Recruiting the pharmacokinetic parameters estimated from noninvasive methods such as Dynamic Contrast Enhanced MRI (DCE-MRI) to evaluate or plan treatment procedure is widely interested in clinical practices. Interpretation of the DCE-MRI data are highly dependent to precision and accuracy of the estimated parameters. One of the most effective factors on the DCE-MR images and consequently on the contrast concentration profile is signal to noise ratio. This work focuses on the analytically evaluation of the noise effect on accuracy of the estimated PK parameters in DCE-MRI studies.
    Materials and Methods: Tofts model as a popular pharmacokinetic model and model selection technique was used to simulate 3470 time curves of contrast concentration. Maximum likelihood estimator as a minimum variance unbiased estimator was recruited to estimate the PK parameters.  Eleven levels of signal to noise ratios (SNR= 5, 8, 10, 13, 15, 20, 25, 30, 35, 50, Noiseless) were added to the simulated CA concentration profiles. The PK parameters were estimated for 11 series data and then mean percentage error was calculated for estimated parameters.
    Results: The results indicate that the most sensitive parameters to the SNR of the DCE-MR images is inverse transfer constant. A SNR greater than 25 was found to be ensure a reasonable error (<5%) in all models parameters.
    Conclusion: Clinical decision based on the DCE-MRI data analysis and estimated PK parameters needs a good image quality (SNR>25), an accurate and robust estimator and correct pharmacokinetic model selection.

  • XML | PDF | downloads: 229 | views: 390 | pages: 197-203

    Purpose: The aim of this research was to estimation of patient effective dose from digital radiography repeat rate and related factors in two referral hospital in Sari, Iran. 
    Materials and Methods: Entrance skin dose and effective dose per common radiography procedures in digital radiography was measured using the BARACUDA RTI detector. 1724 x-ray exposures were investigated prospectively. The annual number of each radiographic procedure was obtained from the archives of digital radiography departments. Patient cumulative dose was calculation from annual exposures repeat rate(RR) and effective dose per digital radiography procedures.
    Results: Mean exposure RR per examination was 1.2% and total percentage of repeat of all examination was 8.7%. annual cumulative dose(man-sivert) resulted from radiographic RR was, 449.2.  The factors leading to the repetition was include the radiographer error (69%), the X-ray tube and equipment error (10.4%), the patient related error (16.1%) and other cases (4.1%). The average effective dose for each examination was 0.36 mSv.
    Conclusion: Digital radiographic repeat rate increases 1.1 % annual patient effective dose from the base level that receives from current radiographic examination. Inconsistency of the center of the digital panel and the central axis of the X-ray beam and error in selection of the upright or table digital panel are among the most important factors in the repetition of digital radiography.

Literature (Narrative) Review(s)

  • XML | PDF | downloads: 182 | views: 301 | pages: 204-216

    Purpose: This paper aims to review the recent linguistic research carried out with the help of fMRI.
    Materials and Methods: We performed a comprehensive search on ProQuest and Scopus search engines using keywords: "functional MRI", "fMRI", and "linguistics", "phonetics", "semantics", and their synonyms, yielding to a total of 343 articles. We included 23 articles based on full-text review which conducted original research on different aspects of language processing using fMRI. Studies regarding applied linguistics, as well as studies using subjects with any neuropsychological disorders, were excluded.
    Results: Included studies were categorized according to the language areas they investigated, including phonetics and phonological processing; semantics; and syntax. The results show that the auditory cortex of both hemispheres is responsible for phonological comprehension of language at the first level, followed by left dominant processing of suprasegmental language in the superior temporal gyrus and the inferior frontal cortices and the supplementary motor area. During semantic processing of the language, lexical entry takes place in the medial temporal lobe and the hippocampus, while sentential semantic aspects of the language are predominantly processed in the left anterior temporal cortex. The BA 44 area is the major active region during syntax processing.
    Conclusion: The experimental methods in studying language such as fMRI and other neurolinguistics techniques could provide scientific evidence for proving theoretical assumption. Besides, results of such researches can help other scientific developments such as brain mapping and pre-surgical planning.

Technical Note