Determination of Dose Distributions by Monte-Carlo Simulation of 6 MV Photon Beam of Varian VitalBeam Accelerator Using Geant4 Multithreaded Code.

Background: Accuracy of dose delivery in radiation therapy is a primary requirement for effective cancer treatment. In practice, dose delivery accuracy of ±5% is desired. To achieve this accuracy level, an accurate method for calculating the dose distributions in the tumor volume is required. Monte-Carlo method is one of the methods considered to be the most accurate for calculating dose distributions. Materials and Methods: G4 linac-MT code was used to simulate a 6 MV photon beam. The initial electron beam parameters were tuned to validate the beam modeling from depth doses and beam profile. The dose distributions measured in water phantom were compared to the calculated dose distributions based on gamma index criterion. Results: The beam tuning showed the initial electron energy, sigma and full width at half maximum of 6.2 MeV, 0.8 MeV, and 1.18 mm, respectively, best match the measured dose distributions. The gamma index tests showed the calculated depth doses and beam profile were generally comparable with measurements, passing the standard acceptance criterion of 2%/2 mm. The simulated photon beam was justified by the index of beam quality, which showed excellent agreement with measured doses with a discrepancy of 0.1%. Conclusion: The observed agreement confirm the accuracy of the simulated 6 MV photon beam. It can therefore be used as radiation source for calculating dose distributions and further investigations aimed at improving dose delivery and planning in cancer patients.

CHALLENGES IN CLINICAL PRACTICE OF CR MAMMOGRAPHY IN TANZANIA.

The aim of this study was to evaluate the clinical practice of CR mammography in Tanzania. The equipment performance and operational conditions were studied; and mean glandular dose (DG) estimated to 75 women undergoing diagnosis at three mammography facilities. All mammograms during this study were reported to be useful for the intended diagnosis. The median DG for craniocaudal and mediolateral oblique projections ranged from 1.27 ± 0.18 mGy to 1.9 ± 0.27 mGy and from 1.3 ± 0.18 mGy to 1.9 ± 0.27 mGy, respectively, and were below the national regulatory guidance of 2.5 mGy. Despite this positive result, unavoidable inappropriate use of beam quality and tube loading settings which could have been through appropriate staff training and performing routine quality control were not uncommon. This work provides an insight of current operational conditions of CR in Tanzania and what strategy should be employed to this service to improve patient care in the country.

Application of off-line image processing for optimization in chest computed radiography using a low cost system.

 The objective of this study was to improve the visibility of anatomical details by applying off-line postimage processing in chest computed radiography (CR). Four spatial domain-based external image processing techniques were developed by using MATLAB software version 7.0.0.19920 (R14) and image processing tools. The developed techniques were implemented to sample images and their visual appearances confirmed by two consultant radiologists to be clinically adequate. The techniques were then applied to 200 chest clinical images and randomized with other 100 images previously processed online. These 300 images were presented to three experienced radiologists for image quality assessment using standard quality criteria. The mean and ranges of the average scores for three radiologists were characterized for each of the developed technique and imaging system. The Mann-Whitney U-test was used to test the difference of details visibility between the images processed using each of the developed techniques and the corresponding images processed using default algorithms. The results show that the visibility of anatomical features improved significantly (0.005 ≤ p ≤ 0.02) with combinations of intensity values adjustment and/or spatial linear filtering techniques for images acquired using 60 ≤ kVp ≤ 70. However, there was no improvement for images acquired using 102 ≤ kVp ≤ 107 (0.127 ≤ p ≤ 0.48). In conclusion, the use of external image processing for optimization can be effective in chest CR, but should be implemented in consultations with the radiologists.

Quality Control Measures in Tanzania: Is it Done?

BACKGROUND: Regular implementation of a quality control (QC) programme in diagnostic radiology is vital if consistent optimal equipment performance, quality images, and accurate diagnosis at optimum radiation dose and costs are to be achieved. This highlighted the necessity for the Tanzania Atomic Energy Commission (TAEC) to establish a training programme to enable radiographers to implement a QC programme in their departments because there are no clinical medical physicists in diagnostic radiology in the country. However, the status of programme implementation is not precisely known. AIM: The aim of this study was to investigate the status of implementation of the QC measures as performed by radiographers in diagnostic radiography departments in Tanzania. METHOD: A quantitative cross-sectional survey, using a questionnaire, was conducted on a sample of 84 radiographers who had been trained in the QC programme and who were practising in 54 hospitals within Tanzania. RESULTS: A large number of respondents were not implementing the following QC tests: tube output, kV, mAs and timer (94%), collimation (53.5%), and densitometry and sensitometry (87.7%). The tests for film viewing box and lead rubber protective apparel were not implemented by 64.2% and 59% of the respondents, respectively. The cassette inspection and darkroom inspection were reported as being implemented by most respondents, although the testing was not observing the recommended schedule. Furthermore, the departments had no records and procedures for the QC programme, and only the locally improvized QC test tools were reported to be available. CONCLUSION: The QC training objectives of TAEC have not been largely achieved because radiographers are not adequately implementing the QC programme. Without the QC programme in place, equipment malfunctioning will not be revealed at an early stage, and this can cause poor image quality and/or higher dose to patients. Therefore, active involvement of the TAEC, the ministry of health, hospital management teams, and radiographers is desirable to achieve full implementation of the programme.

Image quality and dose in mammography in 17 countries in Africa, Asia and Eastern Europe: results from IAEA projects.

PURPOSE: The objective is to study mammography practice from an optimisation point of view by assessing the impact of simple and immediately implementable corrective actions on image quality. MATERIALS AND METHODS: This prospective multinational study included 54 mammography units in 17 countries. More than 21,000 mammography images were evaluated using a three-level image quality scoring system. Following initial assessment, appropriate corrective actions were implemented and image quality was re-assessed in 24 units. RESULTS: The fraction of images that were considered acceptable without any remark in the first phase (before the implementation of corrective actions) was 70% and 75% for cranio-caudal and medio-lateral oblique projections, respectively. The main causes for poor image quality before corrective actions were related to film processing, damaged or scratched image receptors, or film-screen combinations that are not spectrally matched, inappropriate radiographic techniques and lack of training. Average glandular dose to a standard breast was 1.5 mGy (mean and range 0.59-3.2 mGy). After optimisation the frequency of poor quality images decreased, but the relative contributions of the various causes remained similar. Image quality improvements following appropriate corrective actions were up to 50 percentage points in some facilities. CONCLUSIONS: Poor image quality is a major source of unnecessary radiation dose to the breast. An increased awareness of good quality mammograms is of particular importance for countries that are moving towards introduction of population-based screening programmes. The study demonstrated how simple and low-cost measures can be a valuable tool in improving of image quality in mammography.

Patient doses in radiographic examinations in 12 countries in Asia, Africa, and Eastern Europe: initial results from IAEA projects.

OBJECTIVE: The purpose of this study was to survey image quality and the entrance surface air kerma for patients in radiographic examinations and to perform comparisons with diagnostic reference levels. SUBJECTS AND METHODS: In this multinational prospective study, image quality and patient radiation doses were surveyed in 12 countries in Africa, Asia, and Eastern Europe, covering 45 hospitals. The rate of unsatisfactory images and image quality grade were noted, and causes for poor image quality were investigated. The entrance surface doses for adult patients were determined in terms of the entrance surface air kerma on the basis of X-ray tube output measurements and X-ray exposure parameters. Comparison of dose levels with diagnostic reference levels was performed. RESULTS: The fraction of images rated as poor was as high as 53%. The image quality improved up to 16 percentage points in Africa, 13 in Asia, and 22 in Eastern Europe after implementation of a quality control (QC) program. Patient doses varied by a factor of up to 88, although the majority of doses were below diagnostic reference levels. The mean entrance surface air kerma values in mGy were 0.33 (chest, posteroanterior), 4.07 (lumbar spine, anteroposterior), 8.53 (lumbar spine, lateral), 3.64 (abdomen, anteroposterior), 3.68 (pelvis, anteroposterior), and 2.41 (skull, anteroposterior). Patient doses were found to be similar to doses in developed countries and patient dose reductions ranging from 1.4% to 85% were achieved. CONCLUSION: Poor image quality constitutes a major source of unnecessary radiation to patients in developing countries. Comparison with other surveys indicates that patient dose levels in these countries are not higher than those in developed countries.