Unnecessary Dose Research Articles

The prevalence of abnormal findings in screening CT brains performed on patients admitted with psychiatric symptoms

Background: No clear guidelines exist regarding the role of computerised tomography (CT) as a screening neuroimaging tool in psychiatric practice. The aim of this study was to evaluate the usefulness of historical and clinical parameters on the CT request form, identify the spectrum of CT findings and correlate these to develop guidelines for the use of screening CT brains in patients who present with psychiatric symptoms.Methods: Requests and reports for the brain CT’s of 507 consecutive patients over a 2-year period, between 2013 and 2014, referred from a psychiatric institute for screening CT brain scans, were reviewed. Analysis was performed for the history of trauma and seizures, Glasgow Coma Scale (GCS) score, focal neurological signs, papilloedema, electroencephalograph, relevant blood results and abnormal CT findings. All reports were approved by a consultant radiologist.Results: No abnormality was noted in 69% of CT scans. Cerebral atrophy, infarcts, cysts and calcific foci were present in 30% of patients. One patient presenting with focal neurology had a CT demonstrating an extradural haematoma which required neurosurgical intervention. No focal brain lesions, potentially responsible for the psychosis, were identified in any other patient.Conclusion: Routine CT screening of patients who present with psychotic symptoms, in the absence of focal neurological deficit, does not add value to patient outcome, but rather contributes to the escalating health care expenses and unnecessary radiation dose. CT screening of psychiatric patients should be reserved for patients with reliable predictors of intracranial abnormalities such as lateralising signs, seizures, persistent or worsening headaches; decrease in GCS, papilloedema and in patients where the onset of symptoms occurred at an age above 50.

SUGGESTED DIAGNOSTIC REFERENCE LEVELS FOR MAMMOGRAPHY X‑RAY EXAMINATION IN ETHIOPIA

<p><strong>BACKGROUND:</strong> A diagnostic reference levels (DRLs) form an efficient, concise, and powerful standard for optimizing the radiation protection of a patient. OBJECTIVES: To establish the first Ethiopian mammography diagnostic reference level (DRL) as a part of ongoing dose reduction program. <strong>MATERIALS AND METHODS:</strong> A cross‑sectional study was conducted on breast patients having compressed breast thickness (CBT) between 3.7 cm to 5.3 cm in Addis Ababa, Ethiopia. Five mammographic units and 755 mammograms were included in the study period. The mean glandular dose (MGD) was assessed for standard size breast substituted by different polymethyl methacrylate (PMMA) phantoms and imaged under typical clinical conditions in two mammography units. Peak kilo voltage (kVp) and entrance surface air kerma (ESAK) were measured using calibrated digital dosimeter Mult‑O‑Meter Unfors, model 535L, Sweden. The data were analyzed statistically. <strong>RESULT:</strong> The 3rd quartile value of all mammography units and that of private mammography units were found to be 2.37 and 1.73 milligray (mGy), respectively. Hospitals 3rd quartile values of MGD ranges between 1.57 to 7.21 mGy. The MDG based on 4.0 cm polymethyl methacrylate (PMMA) measurements was found to be 1.5 mGy. <strong>CONCLUSION:</strong> Both phantom and patient dose values indicated unnecessary high doses in one government mammography unit. For this mammography unit, urgent dose‑reduction measures and follow‑up actions were recommended. </p>

1437PD - Pooled analysis of treatment-related hypothyroidism with anti-PD-1/PD-L1 therapies in cancer patients

BackgroundBlockade of programmed death 1 (PD-1), or its ligand, PD-L1, could restore T-cell immunity. Anti-PD-1/ or anti-PD-L1 antibodies have demonstrated promising efficacy in the treatment of cancer patients. The toxicity spectrum of PD-1/PD-L1 blockers is distinct from chemotherapy or other target agents. This study aims to investigate the overall incidence of treatment-related hypothyroidism with anti-PD-1/PD-L1 therapies in cancer patients.MethodsA systematic search of literature up to January 2016 was performed in EDLINE, EMBASE, and Cochrane databases to identify relevant clinical trials. Paired reviewers independently selected articles for inclusion and extracted data. Pooled incidence was calculated using Comprehensive Meta-analysis using fixed or random effects model depending the heterogeneity of the included studies.ResultsA total of 23 clinical trials with 5290 patients were included. The overall incidence of all- and high-grade hypothyroidism in cancer patients receiving anti-PD-1/PD-L1 therapies were 7.3% (95% CI, 5.9% to 9.1%) and 0.4% (95% CI, 0.2% to 0.7%), respectively. Adding anti-CTLA-4 antibodies to PD-1/PD-L1 blockers led to increased incidence of all-grade fatigue (16.4% vs. 6.4%, p < 0.001), but not high-grade fatigue (0.3% vs. 0.4%). When stratified by cancer type, trial phase, drug category or drug dosage, no notably differences in the incidence of hypothyroidism were seen.ConclusionsHypothyroidism is commonly seen with anti-PD-1/PD-L1 therapies in cancer patients. Early and appropriate management is required to avoid unnecessary dose reductions and transitory or definitive treatment discontinuations.Legal entity responsible for the study: Sun Yat-sen University Cancer CenterFundingNational Natural Science Funds of China (Grant No: 81372502)DisclosureAll authors have declared no conflicts of interest. BackgroundBlockade of programmed death 1 (PD-1), or its ligand, PD-L1, could restore T-cell immunity. Anti-PD-1/ or anti-PD-L1 antibodies have demonstrated promising efficacy in the treatment of cancer patients. The toxicity spectrum of PD-1/PD-L1 blockers is distinct from chemotherapy or other target agents. This study aims to investigate the overall incidence of treatment-related hypothyroidism with anti-PD-1/PD-L1 therapies in cancer patients. Blockade of programmed death 1 (PD-1), or its ligand, PD-L1, could restore T-cell immunity. Anti-PD-1/ or anti-PD-L1 antibodies have demonstrated promising efficacy in the treatment of cancer patients. The toxicity spectrum of PD-1/PD-L1 blockers is distinct from chemotherapy or other target agents. This study aims to investigate the overall incidence of treatment-related hypothyroidism with anti-PD-1/PD-L1 therapies in cancer patients. MethodsA systematic search of literature up to January 2016 was performed in EDLINE, EMBASE, and Cochrane databases to identify relevant clinical trials. Paired reviewers independently selected articles for inclusion and extracted data. Pooled incidence was calculated using Comprehensive Meta-analysis using fixed or random effects model depending the heterogeneity of the included studies. A systematic search of literature up to January 2016 was performed in EDLINE, EMBASE, and Cochrane databases to identify relevant clinical trials. Paired reviewers independently selected articles for inclusion and extracted data. Pooled incidence was calculated using Comprehensive Meta-analysis using fixed or random effects model depending the heterogeneity of the included studies. ResultsA total of 23 clinical trials with 5290 patients were included. The overall incidence of all- and high-grade hypothyroidism in cancer patients receiving anti-PD-1/PD-L1 therapies were 7.3% (95% CI, 5.9% to 9.1%) and 0.4% (95% CI, 0.2% to 0.7%), respectively. Adding anti-CTLA-4 antibodies to PD-1/PD-L1 blockers led to increased incidence of all-grade fatigue (16.4% vs. 6.4%, p < 0.001), but not high-grade fatigue (0.3% vs. 0.4%). When stratified by cancer type, trial phase, drug category or drug dosage, no notably differences in the incidence of hypothyroidism were seen. A total of 23 clinical trials with 5290 patients were included. The overall incidence of all- and high-grade hypothyroidism in cancer patients receiving anti-PD-1/PD-L1 therapies were 7.3% (95% CI, 5.9% to 9.1%) and 0.4% (95% CI, 0.2% to 0.7%), respectively. Adding anti-CTLA-4 antibodies to PD-1/PD-L1 blockers led to increased incidence of all-grade fatigue (16.4% vs. 6.4%, p < 0.001), but not high-grade fatigue (0.3% vs. 0.4%). When stratified by cancer type, trial phase, drug category or drug dosage, no notably differences in the incidence of hypothyroidism were seen. ConclusionsHypothyroidism is commonly seen with anti-PD-1/PD-L1 therapies in cancer patients. Early and appropriate management is required to avoid unnecessary dose reductions and transitory or definitive treatment discontinuations.Legal entity responsible for the study: Sun Yat-sen University Cancer Center Hypothyroidism is commonly seen with anti-PD-1/PD-L1 therapies in cancer patients. Early and appropriate management is required to avoid unnecessary dose reductions and transitory or definitive treatment discontinuations.

Cutaneous Complications of Targeted Melanoma Therapy.

The landscape of advanced and metastatic melanoma therapy has shifted dramatically in recent years. Since 2011, eight drugs (ipilimumab, vemurafenib, dabrafenib, trametinib, cometinib, pembrolizumab, nivolumab, and talimogene laherparepvec) have received FDA approval for the treatment of advanced or metastatic melanoma, including combination regimens of both small molecule kinase and immune checkpoint inhibitors. These therapies have revolutionized the management of unresectable regional nodal and distant melanoma, providing hope of extended survival to patients. As the use of novel agents has increased, so have the cutaneous toxicities associated with these medications. While most skin reactions are low-grade and can be managed conservatively with topical therapies, malignant lesions and more serious or life-threatening drug reactions can arise during therapy, requiring prompt dermatologic recognition and treatment in order to improve patient outcome. Given the survival benefit attributed to these new agents, treating skin toxicity and maintaining patient quality of life is of paramount importance. Oncologists should be aware of the common cutaneous toxicities associated with these medications and should be encouraged to involve dermatologists in the collaborative care of advanced melanoma patients. Close communication between oncologists and dermatologists can help to avoid unnecessary dose reduction or treatment discontinuation and identify situations when treatment cessation is truly warranted.

Assessment of radiation dose received by prostate cancer and critical organs in 2D and 3D treatment planning

Introduction The goal of radiotherapy treatment planning is to design a beam configuration which will deliver a homogeneous dose to the specified planning target volume (PTV), ensuring that normal tissue receives a reasonably low dose and that critical organs receive less than their tolerance doses. Purpose This study was to compare between 2-dimensional and 3-dimensional techniques for external-beam radiation treatment for prostate cancer. Materials and methods Dose homogeneity within the target volume and doses to critical organs, OAR were evaluated. CT scans of 30 patients with localized prostate cancer were acquired and transferred to the treatment planning systems (TPS). The target volume and uninvolved structures were contoured on axial CT slices throughout the volume of interest. A comparison of the two treatment techniques was performed using isodose distributions, and dose-volume histograms. Results The dose distribution in 2D and 3D technique were found the same; however, in 2D technique delivers unnecessary radiation doses to the rectum and bladder. For the rectum it was found that the average (V70, V75 and D95) in 2D technique 35.5%, 32.2%, 34% while for 3D: 8.4%, 0.2%, 12%, respectively. For the bladder it also found the average (V40, V65) in 2D technique 80.8%, 74.9% while for 3D 20.4%, 17%, respectively, also the right and left hip in 2D technique the average V50 were 17%, 20%, while for 3D technique were 4%, 3% respectively; so these indicates that the doses in organ at risk in 3D were within limit while in 2D higher than the allowable limit causing a risk to OAR. Also for the planning target volume the average (V95%, V107%) in 2D technique 90.6%, 5.7% while, for 3D technique 94.9%, 3.8 respectively. Conclusion 3D conformal radiotherapy was shown to be more effective than 2D conventional radiotherapy in decreasing dose to rectum, bladder and both hip but dose distribution, homogeneity and dose coverage to PTV the same. There was no statistical difference between 2D and 3D radiotherapy in terms of V95% or V107% keeping a minimum of 95% dose coverage for PTV and a maximum dose below 107% as recommended by the ICRU planning guidelines.

Myelosuppression by chemotherapy in obese patients with gynecological cancers.

The American Society of Clinical Oncology provides clinical practice guidelines for appropriate cytotoxic chemotherapy dosing for obese adult patients with cancer. The panel recommends that actual body weight should be used when selecting cytotoxic chemotherapy doses regardless of obesity status. However, there have been no reports regarding the appropriate cytotoxic chemotherapy dosing for obese Japanese patients with cancer. We collected data from 216 gynecological cancer patients who were treated with at least one course of a paclitaxel and carboplatin (TC) regimen or a docetaxel and carboplatin (DC) regimen at Niigata University Medical and Dental Hospital from July 2006 to April 2014. Patients were divided into three groups according to body mass index (BMI): obese (BMI≥25), normal (BMI 18.5-24.9), and underweight (BMI<18.5), as defined by the Japan Society for the Study of Obesity. We analyzed hematological toxicities by full weight-based chemotherapy in each group. The rates of grade 3/4 leukocytopenia, neutropenia, and thrombocytopenia were not significantly different among the three BMI groups on all patient analyses. For the TC regimen, the obese and normal groups had significantly lower leukocytopenia (grade 3/4) rates than did the underweight group. Also, significant positive correlations between BMI and the nadirs of leukocytes, neutrophils, platelets, and hemoglobin were observed. For the DC regimen, no significant difference was observed among the BMI groups and the rate of grade 3/4 hematological toxicities. We did not observe stronger myelosuppression in obese cancer patients compared with non-obese cancer patients. Therefore, the cytotoxic chemotherapy dose should be calculated by the actual body weight and unnecessary dose reduction should be avoided.

SU‐F‐J‐183: Interior Region‐Of‐Interest Tomography by Using Inverse Geometry System

Purpose:The inverse geometry computed tomography (IGCT) composed of multiple source and small size detector has several merits such as reduction of scatter effect and large volumetric imaging within one rotation without cone‐beam artifact, compared to conventional cone‐beam computed tomography (CBCT). By using this multi‐source characteristics, we intend to present a selective and multiple interior region‐of‐interest (ROI) imaging method by using a designed source on‐off sequence of IGCT.Methods:All of the IGCT sources are operated one by one sequentially, and each projection in the shape of narrow cone‐beam covers its own partial volume of full field of view (FOV) determined from system geometry. Thus, through controlling multi source operation, limited irradiation within ROI is possible and selective radon space data for ROI imaging can be acquired without additional X‐ray filtration. With this feature, we designed a source on‐off sequence for multi ROI‐IGCT imaging, and projections of ROI‐IGCT were generated by using the on‐off sequence. Multi ROI‐IGCT images were reconstructed by using filtered back‐projection algorithm. All these imaging process of our study has been performed by utilizing digital phantom and patient CT data. ROI‐IGCT images of the phantom were compared to CBCT image and the phantom data for the image quality evaluation.Results:Image quality of ROI‐IGCT was comparable to that of CBCT. However, the distal axial‐plane from the FOV center, large cone‐angle region, ROI‐IGCT showed uniform image quality without significant cone‐beam artifact contrary to CBCT.Conclusion:ROI‐IGCT showed comparable image quality and has the capability to provide multi ROI image within a rotation. Projection of ROI‐IGCT is performed by selective irradiation, hence unnecessary imaging dose to non‐interest region can be reduced. In this regard, it seems to be useful for diagnostic or image guidance purpose in radiotherapy such as low dose target localization and patient alignment.This research was supported by the Mid‐career Researcher Program through NRF funded by the Ministry of Science, ICT &amp; Future Planning of Korea (NRF‐2014R1A2A1A10050270) and by the Radiation Technology R&amp;D program through the National Research Foundation of Korea funded by the Ministry of Science, ICT &amp; Future Planning (No. 2013M2A2A7038291)

WE‐DE‐207B‐11: Implementation of Size‐Specific 3D Beam Modulation Filters On a Dedicated Breast CT Platform Using Breast Immobilization

Purpose:To implement a 3D beam modulation filter (3D‐BMF) in dedicated breast CT (bCT) and develop a method for conforming the patient's breast to a pre‐defined shape, optimizing the effects of the filter. This work expands on previous work reporting the methodology for designing a 3D‐BMF that can spare unnecessary dose and improve signal equalization at the detector by preferentially filtering the beam in the thinner anterior and peripheral breast regions.Methods:Effective diameter profiles were measured for 219 segmented bCT images, grouped into volume quintiles, and averaged within each group to represent the range of breast sizes found clinically. These profiles were then used to generate five size‐specific computational phantoms and fabricate five size‐specific UHMW phantoms. Each computational phantom was utilized for designing a size‐specific 3D‐BMF using previously reported methods. Glandular dose values and projection images were simulated in MCNP6 with and without the 3DBMF using the system specifications of our prototype bCT scanner “Doheny”. Lastly, thermoplastic was molded around each of the five phantom sizes and used to produce a series of breast immobilizers for use in conforming the patient's breast during bCT acquisition.Results:After incorporating the 3D‐BMF, MC simulations estimated an 80% average reduction in the detector dynamic range requirements across all phantom sizes. The glandular dose was reduced on average 57% after normalizing by the number of quanta reaching the detector under the thickest region of the breast.Conclusion:A series of bCT‐derived breast phantoms were used to design size‐specific 3D‐BMFs and breast immobilizers that can be used on the bCT platform to conform the patient's breast and therefore optimally exploit the benefits of the 3D‐BMF. Current efforts are focused on fabricating several prototype 3D‐BMFs and performing phantom scans on Doheny for MC simulation validation and image quality analysis.Research reported in this paper was supported in part by the National Cancer Institute of the National Institutes of Health under award R01CA181081. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institue of Health.

A radiation oncologist’s guide to contour the parotid gland

The parotid gland is the largest of the salivary glands and is primarily responsible for salivation and prevention of dry mouth as well as oral health. Routinely, the parotid gland is near target in head and neck cancer cases. It is critical that attention be given to avoid unnecessary dose to the parotid glands to preserve saliva, taste, and oral health. The facial nerve (CN VII) passes through the gland and divides it into the superficial and deep lobes. Anteriorly, it overlies the lateral surface of the masseter muscle; laterally, it is surrounded by subcutaneous fat planes of the cheek; and posterosuperiorly, it is bounded by the external auditory canal. The deep lobe is medial to CN VII and is bound by the parapharyngeal space medially, the mastoid process of the temporal bone posteriorly, and the ramus of the mandible anteriorly. Superiorly, the deep lobe extends to the level of the stylomastoid foramen.1,2 It should be noted that, inferiorly, below the angle of the mandible, the parotid tail inserts between platysma and sternocleidomastoid muscle in the area of the posterior submandibular space. Although the gland is divided into the 2 lobes, this anatomical distinction does not aid in the contouring process. However, the retromandibular vein, which is seen coursing through the deep lobe just along the medial margin of CN VII, may be useful for the radiation oncologist. There may be circumstances in which it would

Pharmacodynamic Analysis of Morphine Time-to-Remedication Events in Infants and Young Children After Congenital Heart Surgery.

The aim of this study was to characterize the relationship between morphine plasma concentration and repeated time to postoperative remedication events in children undergoing cardiac surgery. Data from our previously published study of morphine pharmacokinetics were utilized in this pharmacodynamic study. A population survival analysis based on hazard functions was undertaken in NONMEM(®). Hazard was best described by a Gompertz function changing in steps over time. Concentration and age were the only predictors of the hazard function. Concentration producing 50% reduction in hazard was 19.6 (bootstrap 95% confidence interval 5.90-49.5ng/ml). The hazard ratio for a 1-year-old child to a 1-month-old child was 1.91 (1.35-2.86). Sensitivity to morphine decreased with age and leveled off after 1-year of life. Morphine sulfate doses >0.1mg/kg did not noticeably increase tolerable pain durations. Time to remedication is a clinically useful endpoint for assessing opioid-induced analgesia. Sensitivity to morphine treatment is age-dependent. Morphine sulfate doses of 0.1-0.2mg/kg are adequate for the management of postoperative pain in children. Our findings may help avoid unnecessary large morphine doses in children.

Hidden Barriers to Delivery of Pharmacological Venous Thromboembolism Prophylaxis

Standardized electronic order sets for venous thromboembolism prophylaxis have increased the proportion of patients receiving venous thromboembolism prophylaxis. However, ordering venous thromboembolism prophylaxis does not ensure consistent administration. To explore causes of variability in the rate of administration of ordered doses of pharmacological venous thromboembolism prophylaxis among hospital units. Mixed methods study, including qualitative observation and quantitative nursing survey administration. Nurses included in observations were practicing on an inpatient unit, caring for patients with orders to receive venous thromboembolism prophylaxis consisting of low-dose unfractionated heparin or low-molecular weight heparin. Nurses on 12 inpatient units with disparate rates of administration were included in the survey. Qualitative observation data were collected until thematic saturation was achieved. Survey was conducted to identify beliefs and practices surrounding nursing administration of venous thromboembolism prophylaxis. During observations, some nurses presented pharmacological venous thromboembolism prophylaxis to their patients as an optional therapy. Nurses on low-performing units are more likely to believe that pharmacological venous thromboembolism prophylaxis is ordered for patients who do not require it. More often, they also acknowledge that nurses use their clinical decision-making skills to determine when to omit unnecessary doses of prescribed venous thromboembolism prophylaxis. Nurses on units with low administration rates often believe they have the skills to determine which patients require pharmacological venous thromboembolism prophylaxis. They are also more likely to believe that ordered doses are discretionary and offer the medication as optional to patients.

Reduction in radiation doses from paediatric CT scans in Great Britain.

Although CT scans provide great medical benefits, concerns have been raised about the magnitude of possible associated cancer risk, particularly in children who are more sensitive to radiation than adults. Unnecessary high doses during CT examinations can also be delivered to children, if the scan parameters are not adjusted for patient age and size. We conducted the first survey to directly assess the trends in CT scan parameters and doses for paediatric CT scans performed in Great Britain between 1978 and 2008. We retrieved 1073 CT film sets from 36 hospitals. The patients were 0-19 years old, and CT scans were conducted between 1978 and 2008. We extracted scan parameters from each film including tube current-time product [milliampere seconds (mAs)], tube potential [peak kilovoltage (kVp)] and manufacturer and model of the CT scanner. We estimated the mean mAs for head and trunk (chest and abdomen/pelvis) scans, according to patient age (0-4, 5-9, 10-14 and 15-19 years) and scan year (<1990, 1990-1994, 1995-1999 and ≥2000), and then derived the volumetric CT dose index and estimated organ doses. For head CT scans, mean mAs decreased by about 47% on average from before 1990 to after 2000, with the decrease starting around 1990. The mean mAs for head CTs did not vary with age before 1990, whereas slightly lower mAs values were used for younger patients after 1990. Similar declines in mAs were observed for trunk CTs: a 46% decline on an average from before 1990 to after 2000. Although mean mAs for trunk CTs did not vary with age before 1990, the value varied markedly by age, from 63 mAs for age 0-4 years compared with 315 mAs for those aged >15 years after 2000. No material changes in kVp were found. Estimated brain-absorbed dose from head CT scans decreased from 62 mGy before 1990 to approximately 30 mGy after 2000. For chest CT scans, the lung dose to children aged 0-4 years decreased from 28 mGy before 1990 to 4 mGy after 2000. We found that mAs for head and trunk CTs was approximately halved starting around 1990, and age-specific mAs was generally used for paediatric scans after this date. These changes will have substantially reduced the radiation exposure to children from CT scans in Great Britain. The study shows that mAs and major organ doses for paediatric CT scans in Great Britain began to decrease around 1990.

Management of Dermatologic Complications of Lung Cancer Therapies.

In recent years, oncogene-directed targeted agents and immunotherapies have expanded the treatment armamentarium for advanced lung cancer and, in particular, non-small cell lung cancer (NSCLC). Along with extended survival, these agents are accompanied by a host of cutaneous complications that affect the skin, hair, and nails. These skin complications range from the well-characterized papulopustular (acneiform) eruption of the epidermal growth factor receptor (EGFR) inhibitors to the emerging characterization of lichenoid skin eruptions seen during treatment with antibodies targeting the programmed cell death protein 1 (PD-1) and programmed cell death protein 1 ligand (PD-L1). When promptly recognized and accurately diagnosed, most cutaneous adverse events can be managed with supportive treatments, avoiding the need to interrupt antitumor therapy. Furthermore, preemptive management of skin problems can lead to significantly decreased severity of many cutaneous complications of these therapies. We encourage close collaboration between dermatologists and oncologists to better characterize cutaneous toxicity, select appropriate management, and avoid unnecessary dose reduction or discontinuation while simultaneously improving patient quality of life.

Assessment of patient dose and optimization levels in chest and abdomen CR examinations at referral hospitals in Tanzania.

The aim of this study was to evaluate the radiation doses to patient during chest and abdomen CR examinations, and assess the related level of optimization at five referral hospitals in Tanzania. The international code of practice for dosimetry in diagnostic radiology was applied to determine the entrance surface air kerma (ESAK) to patients. The level of optimization was assessed from low‐contrast objects scores of phantom images at different exposures. The results show that mean ESAK varied from 0.16 to 0.37 mGy for chest PA and from 2 to 6 mGy for abdomen AP. Assuming similar patient and phantom attenuations, the optimization performed at all facilities was consistent with phantom evaluations in terms of tube potential settings in use. However, all facilities seemed to operate at higher tube load values above 5 mAs for chest examination, which can lead to unnecessary patient doses. Inadequate initial training on CR technology explains in large proportion the inappropriate use of exposure parameters.PACS numbers: 87.50.up, 87.59bd

O.31 - The effect of collimation on the radiation dose received by neonates

Introduction: The rate of preterm births has increased since 1990. Preterm birth leads to less development time for the baby, leading to medical problems. These premature babies need special care and multiple radiographic examinations. Babies are still developing and possess many rapidly dividing cells, making them more susceptible to low levels of ionizing radiation. The dose received is influenced by a few controllable parameters. A difficult to control parameter that influences dose is the collimation used. Diagnostic X-ray examinations of neonates usually include the chest, abdomen or a combined image of both called a baby-gram. The aim was to determine the effect of collimation on the amount of unnecessary radiation dose received by neonates.

An investigation of kV CBCT image quality and dose reduction for volume-of-interest imaging using dynamic collimation.

The focus of this work was to investigate the improvements in image quality and dose reduction for volume-of-interest (VOI) kilovoltage-cone beam CT (CBCT) using dynamic collimation. A prototype iris aperture was used to track a VOI during a CBCT acquisition. The current aperture design is capable of 1D translation as a function of gantry angle and dynamic adjustment of the iris radius. The aperture occupies the location of the bow-tie filter on a Varian On-Board Imager system. CBCT and planar image quality were investigated as a function of aperture radius, while maintaining the same dose to the VOI, for a 20 cm diameter cylindrical water phantom with a 9 mm diameter bone insert centered on isocenter. Corresponding scatter-to-primary ratios (SPR) were determined at the detector plane with Monte Carlo simulation using EGSnrc. Dose distributions for various sizes VOI were modeled using a dynamic BEAMnrc library and DOSXYZnrc. The resulting VOI dose distributions were compared to full-field distributions. SPR was reduced by a factor of 8.4 when decreasing iris diameter from 21.2 to 2.4 cm (at isocenter). Depending upon VOI location and size, dose was reduced to 16%-90% of the full-field value along the central axis plane and down to 4% along the axis of rotation, while maintaining the same dose to the VOI compared to full-field techniques. When maintaining constant dose to the VOI, this change in iris diameter corresponds to a factor increase of approximately 1.6 in image contrast and a factor decrease in image noise of approximately 1.2. This results in a measured gain in contrast-to-noise ratio by a factor of approximately 2.0. The presented VOI technique offers improved image quality for image-guided radiotherapy while sparing the surrounding volume of unnecessary dose compared to full-field techniques.

X-ray beam design for multi-energy imaging with charge-integrating detector: A simulation study

Multi-energy X-ray imaging systems have been widely used for clinical examinations. In order to enhance the imaging quality of these X-ray systems, a dual-energy system that can obtain specific information has been developed in order to discriminate different materials. Although the dual-energy system shows reliable performance for clinical applications, it is necessary to improve the method in order to minimize radiation dose, reduce projection error, and increase image contrast. The purpose of this study is to develop a triple energy technique that can discriminate three materials for the purpose of enhancing imaging quality and patient safety. The X-ray system tube voltage was varied from 40 to 90kV, and filters (that can generate three X-ray energies) were installed, consisting of pure elemental materials in foil form (including Al, Cu, I, Ba, Ce, Gd, Er, and W). The X-ray beam was evaluated with respect to mean energy ratio, contrast variation ratio, and exposure efficiency. In order to estimate the performance of the suggested technique, Monte Carlo was conducted, and the results were compared to the photon-counting method. As a result, the density maps of iodine, aluminum, and polymethyl methacrylate (PMMA) using the X-ray beam were more accurate in comparison to that obtained with the photon-counting method. According to the results, the suggested triple energy technique can improve the accuracy of the determination of thickness of density. Moreover, the X-ray beam could reduce unnecessary patient dose.

Correlation Between Exposure Rate and Residual Activity in Felines Undergoing 131I Thyroid Ablation Therapy.

Radioiodine thyroid ablation therapy is a common method for treatment of felines exhibiting hyperthyroidism. Due to the high gamma-ray emission rate of radioiodine (I), patients following treatment must be held in isolation for several days before release to prevent unnecessary dose to owners and members of the public. Dose rate measurement on the external surface of the patient of ≤ 20 μSv h is maintained as the patient release criterion without regard to residual activity. However, the Texas Department of State Health Services regulatory guide recommends a release limit of 3.7 MBq to households with non-pregnant women and children over the age of 18 y, and a limit of 925 kBq to households of pregnant women and children who can be supervised. In this paper, Monte Carlo computational radiation transport techniques are employed to predict and standardize the patient isolation time at the clinic by correlating the thyroid burden and surface dose rates of felines. Measurements of patient dose rate as a function of time are used to determine the patient-specific effective half-life experimentally and to validate the model results. Results show that an average holding time of 8 to 9 d is sufficient to reduce the residual activity to 3.7 MBq levels. Additionally, contact dose rate measurements of 20 μSv h or less correlate to residual activity levels of approximately 925 kBq. Based on the model and measurements, a protocol was developed for clinical use at Texas A&M University Veterinary Medical Teaching Hospital to allow estimation of residual activity following injection. This in turn confirms that the surface dose rates used as the release criteria follow the release limits recommended in the regulatory guide.

Liquid Li based neutron source for BNCT and science application

Liquid lithium (Li) is a candidate material for a target of intense neutron source, heat transfer medium in space engines and charges stripper. For a medical application of BNCT, epithermal neutrons with least energetic neutrons and γ-ray are required so as to avoid unnecessary doses to a patient. This is enabled by lithium target irradiated by protons at 2.5MeV range, with utilizing the threshold reaction of 7Li(p,n)7Be at 1.88MeV. In the system, protons at 2.5MeV penetrate into Li layer by 0.25mm with dissipating heat load near the surface. To handle it, thin film flow of high velocity is important for stable operation. For the proton accelerator, electrostatic type of the Schnkel or the tandem is planned to be employed. Neutrons generated at 0.6MeV are gently moderated to epithermal energy while suppressing accompanying γ-ray minimum by the dedicated moderator assembly.

Evaluation of Computed Tomography Scan Ability in Detecting Chest Nodules Using Tissue Equivalent Phantom

Aim of Study: The lung cancer is noted at the end stages of disease, the morbidity and mortality rate related to is higher than others. To minimize this rate, early diagnosis of lung solitary nodules before spreading metastases to lymph nodes and other organs is of consideration. At the moment, Computerized Tomography is one of the most important modalities in diagnosing lung solitary nodules, however the CT exposure rates are much higher than diagnostic radiology field. Therefore it is necessary to do evaluation of CT. Scan ability in detecting chest nodules for preventing unnecessary radiation dose to patient. Materials and Methods: In this study, a chest phantom including different nodules of sizes and types was designed. Imaging of phantom was performed by TOSHIBA spiral CT of Imam Khomaini medical complex and GE spiral CT of Fayyazbakhsh hospital with 5,3,1 mm slices and 80, 120 kVp and 50,60,80,100 mA. Results: This study revealed, 4 mm width nodules were noted both in slices with 120 kV and 50, 100 mA and 3, 5 mm thickness and in 80 kV and 60 mA with 3 mm thickness. The calcium carbonated particles were noted in 6, 8, and 10 mm whitish but not in smaller nodules; however a low density of carbonated calcium was noted just in 10 mm width nodules. Conclusion: CT.scan is a useful technique for detection of lung tumor with sizes more than 4mm. Keywords: Chest nodules, CT.Scan, Chest Phantom.