Evaluation of average glandular dose (AGD) in screening and diagnostic digital mammography and digital breast tomosynthesis (DBT) towards establishing a reference dose range band (DRB): a developing country experience.

This study represents the first national survey conducted in Sri Lanka to establish national diagnostic reference levels (NDRLs) for screening and diagnostic acquisitions in digital mammography (2D-DM) and digital breast tomosynthesis (DBT). Additionally, the study investigated the relationship between average glandular dose (AGD) and compressed breast thickness (CBT) and introduced a novel concept called dose range bands (DRBs) as a tool for optimizing radiation dose in mammography. DICOM metadata was used to extract dose data and exposure parameters from women undergoing either screening (350) or diagnostic (750) DM. The analysis included both craniocaudal and mediolateral oblique views of each breast, acquired using 2D-DM and DBT imaging techniques. The NDRL (AGD per view) was 1.97 mGy and 2.01 mGy for diagnostic DM and DBT, respectively. The corresponding NDRLs for screening acquisition were 2.44 mGy and 2.30 mGy. The mean DBT/DM AGD ratio was 1.39 and 0.97 for diagnostic and screening, respectively. Further, the association between the average glandular AGD per view and CBT is stronger in DBT than in 2D-DM. The study findings highlight the need for standardisation of compression practices, considering factors such as the radiographer's experience, imaging equipment, breast density, age, breast size, and pain threshold.

EVALUATION OF RADIATION DOSE IN MULTI-SLICE COMPUTED TOMOGRAPHY PROTOCOLS OF HEAD AND NECK REGIONS.

In head and neck computed tomography (CT) imaging, the optimisation of radiation dose is crucial due to the presence of radio-sensitive organs. This study aimed to evaluate the radiation dose in multi-slice CT for head and neck examinations. Volume CT dose index, dose length product and effective dose (E) were assessed for 10 head and neck CT scans performed on 292 adult patients (mean age 49.2 ± 15.9 y). The study resulted in median E values of 0.82, 1.62, 2.43, 0.93, 1.70, 0.83, 3.55, 6.25, 2.19 and 5.26 mSv, respectively, for sinuses (non-contrast (NC)), sinuses (NC) and contrast-enhanced (CE), petrous bone (PTB)/internal auditory meatus (IAM) (NC + CE), PTB/IAM (NC), orbit (NC + CE), orbit (NC), brain with the orbit (NC), brain CT angiography (CTA) subtraction, neck (NC) and brain/neck (NC). Furthermore, the overall radiation doses of this institution were found to be below the values suggested by similar studies. However, optimisation of the dose is required for brain CTA.

AWARENESS OF PAEDIATRIC RADIOLOGICAL PROTECTION AND IMAGING PARAMETERS AMONG GROUP OF SRI LANKAN RADIOGRAPHERS.

The present survey evaluated the level of awareness of radiological protection concepts and imaging parameters among Sri Lankan radiographers for the first time. The data were collected using an electronic questionnaire of 22 questions on demographic data, awareness of radiation protection concepts and imaging parameters. Only 84 out of 122 (68.8%) requested radiographers to return the questionnaire. More than 85% had ≥3 years of experience in the radiography field. The average scores for questions on best practices, imaging parameters and radiation protection were 75, 75.8 and 70.2%, respectively, with an overall score of 73.4%. Significant confusion existed on protective shielding, paediatric consenting capability, use of grids and excess X-ray field during paediatric radiography. Although the overall knowledge and awareness of participants on studied concepts were satisfactory, a continuous professional development credit system and implementation of a code of practice are required to improve the quality of radiography practice.

Dose reference level based on size-specific dose estimate (SSDE) and feasibility of deriving effective body diameter using tube current and time product (mAs) for adult chest and abdomen computed tomography (CT) procedures.

This study aimed to establish dose reference level (NDRLSSDE) based on size-specific dose estimate (SSDE) derived using effective diameter (Deff) for adult chest and abdomen computed tomography (CT) procedures and to explore the feasibility of drivingDeffusing the product of tube current and time (mAs). In this retrospective study, dose data, scan parameters and patient body dimensions at the mid-slice level from 14 CT units (out of 63 total) were extracted. Additionally, the mAs values of the axial slice at the samez-location where the diameter measurements were made (mAsz) were recorded. Pearson's correlation (r) analysis was used to determine the relationship ofDeffwith patient BMI, weight, and mAsz. The NDRLSSDEfor the chest and abdomen were 9.72 mGy and 13.4 mGy, respectively. The BMI and body weight were less correlated (r= 0.24 andr= 0.33, respectively) withDeff. The correlation between mAszandDeffwas considerably strong (r= 0.78) and can be used to predictDeffaccurately. The absolute dose differences between SSDEs calculated using the AAPM-204 method and mAszwas less than 1.1 mGy (15%). Therefore, mAszis an efficient parameter to deriveDeff. Further, the direct conversion factors to estimate SSDEs at different locations along thez-direction in the scan region from corresponding mAs and CTDIvolwere calculated. The NDRLSSDEsuggested in the present study can be used as a reference for size-dependent dose optimisation in Sri Lanka, and existing NDRL based on CTDIvolunderestimate the average adult CT dose by 36.0% and 39.7% for chest and abdomen regions respectively. The results show that using mAszto determine SSDE is a simple and practical approach with an accuracy of 95% and 85% for abdomen and chest scans, respectively. However, the obtained linear relationship betweenDeffand mAs is highly dependent on the ATCM technique and the user-determined noise levels of the scanning protocol. Finally, the phantom study resulted in the strongest correlation (r= 0.99) between theDwzand mAsz, and the prediction of patient size would be more precise thanDeffmethod.

Patient size as a parameter for determining Diagnostic Reference Levels for paediatric Computed Tomography (CT) procedures.

INTRODUCTION: The paediatric radiation dose has never been studied in Sri Lanka, nor has a national diagnostic reference level (NDRL) established. Therefore, the primary aim of this study was to propose diagnostic reference levels (DRL) and achievable dose (AD) values for paediatric CT examinations based on size. METHODS: A total of 658 paediatric (0-15 years) non-contrast-enhanced (NC) studies of head, chest and abdomen regions performed during six months in two dedicated paediatric hospitals (out of the three such institutions in the country) were included. For head examinations, the dose indexes were analysed based on age, while for body examinations, both age and effective diameter (Deff) were used. The median and the third quartile of the pooled dose distribution were given as AD and NDRL, respectively. RESULTS: The AD ranges for the head, chest and abdomen regions based on CTDIvol were 45.8-57.2 mGy, 2.9-10.0 mGy and 3.8-10.3 mGy. The corresponding NDRL ranges were 45.8-95.8 mGy, 3.5-14.1 mGy and 4.5-11.9 mGy. The AD ranges based on SSDEdeff and deff were 3.5-9.6 mGy and 4.1-10.3 mGy in chest and abdomen regions. The corresponding NDRL were 4.5-14.1 mGy and 6.1-10.6 mGy. CONCLUSION: Other institutions can use the present study DRLs as a reference dose for paediatric CT. The AD values can be used as a baseline for target dose optimisations, reducing doses up to 90%.

DETERMINATION OF ENTRANCE SURFACE DOSE FOR THREE COMMON PLANAR DIAGNOSTIC X-RAY EXAMINATIONS.

Patient dose during diagnostic radiography procedures primarily depends on the entrance surface dose (ESD) and the exposure area. The purpose of this study was to determine ESD for five common diagnostic X-ray examinations using dose area product and X-ray tube output. The ESDs were estimated in a sample of 340 patients using normalised X-ray output from Philips-PrimaryDiagnost digital X-ray machine equipped with digital flat panel scintillator detector. The resultant mean ESDs for chest postero-anterior/lateral, lumbar spine antero-posterior (AP)/lateral and abdomen AP were 0.49, 2.00, 5.74, 12.79 and 4.62 mGy, respectively. The mean and third quartile ESD values of this study were significantly higher than the values found in the literature. This can be attributed to the lower tube potential (kVp) values and the higher tube current-time products (mAs). The methodology used here is a better option for low-resources countries for routine dose monitoring.

Dosimetry procedure to verify dose in High Dose Rate (HDR) brachytherapy treatment of cancer patients: A systematic review.

High dose rate (HDR) brachytherapy is a widely accepted cancer treatment method which provides high cure rates. In a HDR brachytherapy treatment, high radiation doses are delivered to the tumor area by placing the radioactive sources in the close proximity to the region of interest. The brachytherapy dose delivery follows the inverse square law with rapid dose fall of leading to minimal damage to the surrounding normal tissue. The safe direct delivery of the radiation dose to the tumour leads to good treatment outcomes comparable to other modalities of treatment. Hence, it is crucial to maintain a sharp drop in the radiation dose distribution within very short distances. Treatment planning system (TPS) which is controlled by a computer algorithm plays a significant role in calculating the optimum doses to the tumour area during a typical HDR brachytherapy treatment. However, the optimum dose calculated by the TPS must be verified by using an independent testing method in order to eliminate under/over irradiation of the tumor region and as quality assurance. In general, two types of independent dose verification methods(experimental and computational) are used to crosscheck the doses calculated by TPS. This systematic review aims to summarize the studies done in the past ten years on HDR brachytherapy treatment planning verification and to analyze the reliability and limitations.

Establishment of national diagnostic reference levels for computed tomography procedures in Sri Lanka: first nationwide dose survey.

The main purpose of this study was to establish for the first time national diagnostic reference levels (NDRLs) for common computed tomography (CT) procedures in Sri Lanka. Patient morphometric data, exposure parameters and dose data such as volume CT dose index (CTDIvol) and dose-length product (DLP) were collected from 5666 patients who underwent 22 types of procedure. The extreme dose values were filtered before analysis to ensure that the data come from standard size patients. The median of the dose distribution was calculated for each institution, and the third quartile value of the median distribution was considered as the NDRL. Based on the inclusion and exclusion criteria, data from 4592 patients and 17 procedure types were considered for establishment of a NDRL, covering 41% of the country's CT machines. The proposed NDRLs based on CTDIvoland DLP were: non-contrast-enhanced (NC) head, 82.2 mGy/1556 mGy cm; contrast-enhanced (CE) head, 82.2 mGy/1546 mGy cm; chest NC, 7.4 mGy/350 mGy cm; chest CE, 8.3 mGy/464 mGy cm; abdomen NC, 10.5 mGy/721 mGy cm; abdomen arterial (A) phase, 13.4 mGy/398 mGy cm; abdomen venous (V) phase, 10.8 mGy/460 mGy cm; abdomen delay (D) phase, 12.6 mGy/487 mGy cm; sinus NC, 30.2 mGy/452 mGy cm; lumbar spine NC, 24.1 mGy/1123 mGy cm; neck NC, 27.5 mGy/670 mGy cm; high-resolution CT of chest, 10.3 mGy/341 mGy cm; kidneys ureters and bladder NC, 19.4 mGy/929 mGy cm; chest to pelvis (CAP) NC, 10.8 mGy/801 mGy cm; CAP A, 10.4 mGy/384 mGy cm; CAP V, 10.5 mGy/534 mGy cm; CAP D, 16.8 mGy/652 mGy cm. Although the proposed NDRLs are comparable with those of other countries, the observed broad dose distributions between the CT machines within Sri Lanka indicate that dose optimisation strategies for the country should be implemented for most of the CT facilities.

Measuring prompt gamma-ray emissions from elements found in tissue during passive-beam proton therapy.

Prompt gamma detection during proton radiotherapy for range verification purposes will need to operate in both active and passive treatment beam environments. This paper describes prompt gamma measurements using a high resolution 2″ × 2″ LaBr3detector for a 200 MeV clinical passive-scatter proton beam. These measurements examine the most likely discrete prompt gamma rays emitted from tissue by detecting gammas produced in water, Perspex, carbon and liquid-nitrogen targets. Measurements were carried out at several positions around the depth corresponding to the location of the Bragg peak for water and Perspex targets in order to investigate prompt gamma emission as a function of depth along the beam path. This work also focused on validating the Geant4 Monte Carlo model of the passive-scatter proton beam line and LaBr3detector by making a direct comparison between the simulated and experimental results. The initial prompt gamma measurements were overwhelmed by the high amount of scattered radiation when measuring at isocenter, shifting the target further downstream from the final collimator significantly reduced the background radiation. Prompt gamma peaks were then clearly identified for the water, Perspex and graphite targets. The developed Geant4 Monte Carlo model was able to replicate the measured prompt gamma ray energy spectra, including production for important photopeaks to within 10%, except for the 4.44 MeV peak from the water target, which had more than a 50% overestimation of the number of produced prompt gamma rays. The prompt gamma measurements at various depths correlated well with the proton dose deposition; the 4.44 and 6.13 MeV photopeak profiles peaked within 1 cm of the Bragg peak and the R50%value for the 3-7 MeV energy range predicted the proton range within 8 mm.

Establishment of regional diagnostic reference levels for digital mammography in Western Province of Sri Lanka.

The radiation dose to the breasts should be kept to a minimum as breast tissues are highly sensitive to radiation. In mammography, the mean glandular dose (MGD) is used to specify the patient dose. In this study, data on the MGD during diagnostic mammographic examinations was collected using the database from six digital mammography facilities available in the Western Province in Sri Lanka. Examinations involving breast pathology, breast implants, or compressed breast thicknesses (CBT) outside the range of 20-110 mm were excluded in this study. The mean MGD per breast was 3.50 mGy, with a mean CBT of 57 mm. The mean MGD per facility varies from 1.58 to 2.27 mGy, with overall 75th and 95th percentiles of 2.15 and 2.82 mGy, respectively. The 75th and 95th percentile MGD per image, for the average CBT of 57 ± 12 mm, were 2.00 and 2.65 mGy respectively. The 75th percentile value of the MGD is suggested for the Western Province and it depends on the specific CBT.

Evaluation of proton inelastic reaction models in Geant4 for prompt gamma production during proton radiotherapy.

During proton beam radiotherapy, discrete secondary prompt gamma rays are induced by inelastic nuclear reactions between protons and nuclei in the human body. In recent years, the Geant4 Monte Carlo toolkit has played an important role in the development of a device for real time dose range verification purposes using prompt gamma radiation. Unfortunately the default physics models in Geant4 do not reliably replicate the measured prompt gamma emission. Determining a suitable physics model for low energy proton inelastic interactions will boost the accuracy of prompt gamma simulations. Among the built-in physics models, we found that the precompound model with a modified initial exciton state of 2 (1 particle, 1 hole) produced more accurate discrete gamma lines from the most important elements found within the body such as 16O, 12C and 14N when comparing them with the available gamma production cross section data. Using the modified physics model, we investigated the prompt gamma spectra produced in a water phantom by a 200 MeV pencil beam of protons. The spectra were attained using a LaBr3 detector with a time-of-flight (TOF) window and BGO active shield to reduce the secondary neutron and gamma background. The simulations show that a 2 ns TOF window could reduce 99% of the secondary neutron flux hitting the detector. The results show that using both timing and active shielding can remove up to 85% of the background radiation which includes a 33% reduction by BGO subtraction.