Multivariate statistical analysis of factors related to mean annual indoor radon concentrations of Greek dwellings

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46300dpm or 733Bq I-125). Reporting wasbased on data from all assays performed throughout 2013.Tube count rates, due to I-125 activity measurement, were summed and converted to I-125 activity by use ofCF. Total number and weight of tubes included in solid waste were reported.Proper time for decay-in-storage was determined, meeting Greek regulations, which allow daily solid waste disposal containing I-125, when activity concentration is below 10Bq/g. Results: During 2013, 47127 tubes were assayed in ”THEAGENEIO”Nuclear Medicine Dept. 472 kits (100 tubes each) of RIA-IRMAtests were consumed, mean valueof I-125traceractivity400kBq/kit. Various hormones and tumor markers were assayed:FT3,FT4,ICTP,TPA,TAG-72,TRAK,FREE PSA,IPTH,HTG,FSH,LH,ACTH,DHEA'S,GH,E2,PROL,AFP,B-CG, PSA,NSE,CA199,TESTOSTERONE,TM-AB,TSH,CA15-3,CgA, CA125,CEA,TG-AB, P4 (PROG),ALDOSTERONE,ІNSULIN,CePEPTIDE,RENIN,17ΟНpPROGESTERONE, CALCITONINE. Calibration factor (CF) was 45 cpm/Bq.Each tube’s weight is 1.5g, therefore total weight of solid waste (including bottles containing tracer in the kit) derived equal to73 kg.Total count rate was 2082932567cpm,leading to a total activity of I-125 46.5MBq/year and an average value of 982Bq/tube. According to lab’s practice, wastes of RIA- IRMA tubes are collected every 2 weeks. 24waste packages, 4 kg each, are stored in a dedicated fridge every year. Considering Greek Radiation Protection Regulation, (FЕΚ 1014(FΟR)94 216/06.03.2001), each waste package must be kept in storage for 363 days. Conclusion: Storage of tubes, contaminated with I-125,for one year is needed before removing them from hospital. Therefore, special storage space, safe for staff, should be provided in each lab. Waste packages used must be plastic. Each one must be assigned an I.D. number, initial storing date, weight, contained activity of I-125, projected date of removal from storage. Before disposal each bag is monitored for activity presence. All persons engaged in this work are trained, ensuring compliance with the department’s procedures.

RADIATION EXPOSURE AND IMAGE QUALITY EVALUATION USING THE IDOSE4 HYBRID ITERATIVE RECONSTRUCTION ALGORITHM IN PEDIATRIC CHEST HRCT Magdalini Smarda a, Efthimia Alexopoulou a, Argyro Mazioti a, Sofia Kordolaimi a, Agapi Ploussi a, Konstantinos Priftis b, Efstathios P. Efstathopoulos a. a 2nd Department of Radiology, Medical School, National and Kapodistrian University of Athens; b Department of Pediatrics, Medical School, National and Kapodistrian University of Athens Background: Computed Tomography (CT) radiation exposure has raised concern, especially in pediatric patients who are more radiosensitive and have longer life expectancy than adults. Therefore, the use of the recently developed Iterative Reconstruction (IR) algorithms is particularly significant for dose reduction. The aim of the study is to compare radiation exposure and image quality between filtered back projection (FBP) and an IR algorithm (iDose4, Philips) in pediatric chest High Resolution Computed Tomography (HRCT). Materials and methods: A total number of 45 pediatric chest HRCT examinations were performed on our Department’s 64-detector row CT scanner before and after the installation of IR algorithm. 21 patients were scanned using the FBP protocol (FBP group) while 24 patients were scanned using iDose4 protocol (iDose4 group). The images of iDose4 group were reconstructed using FBP and all levels of iDose4 algorithm. The tube current-time product (mAs) was reduced for the iDose4 group while the rest exposure settings (kVp, filtration, pitch) were kept constant for both protocols. Radiation exposure quantities (CTDIvol, DLP, ED, SSDE) were evaluated. Image noise was objectively calculated. Subjective image quality was evaluated by 2 experienced radiologists in a 5-point scale.. Unpaired t-tests were used for data statistical analysis. All results were compared on the basis of weight category (higher of lower than 30kg).

Results: For the low-weight category (<30kg), iDose4 application allowed an effective dose reduction of about 80%, whereas in the high-weight category (>30kg) the corresponding reduction was 40%. Comparable results concerning overall subjective image quality between the 2 groups were achieved with iDose4 level 4 for the >30kg subcategory and with iDose4 level 6 for the <30kg subcategory of pediatric patients. The corresponding results concerning objective image noise were noticed between FBP and iDose4 images of levels 3 and 6 for the >30kg and <30kg category respectively. Conclusion: The use of the iDose4 iterative reconstruction algorithm in pediatric chest HRCT enables substantial radiation exposure reduction, without compromising image quality and diagnostic confidence. Further evaluation with lower mAs settings is needed in order to draw more precise conclusions, especially in the high-weighted subcategory of patients. QUALITY AUDITS OF SMALL FIELD OUTPUT FACTORS: A MULTI-CENTRE PILOT STUDY G. Azangwe, P. Grochowska, J. Izewska. International Atomic Energy Agency, Vienna, Austria Background: A new co-ordinated research project (CRP) was launched by the IAEA for the national audit networks for radiotherapy with the purpose of developing the methodology for remotely auditing IMRT related QA. The programme involves three audit steps: (1) remote verification of TPS calculation of small field output factors relevant for IMRT and audit of MLC positional performance, (2) audit of single clinical IMRT field dose delivery and (3) ‘end-to-end’ audit (imaging, planning, dose delivery) for multiple field IMRT techniques. New procedures and phantoms are being developed and examined through multi-centre pilot studies involving CRP participants. Materials and methods: The CRP has attracted research groups from 14 countries across the world. The first study was conducted for the audit of beam output of high energy photon beams for five selected field sizes of 22 cm2 to 1010 cm2, defined by an MLC and corresponding to representative segment sizes used for IMRT treatment planning. The beam outputs calculated by participants’ TPSs were compiled by the IAEA and compared to the datasets published in literature [1]. Results: The results are available for 29 beam/TPS combinations. The agreement within 1%-2% between the TPS calculated output and the literature data was obtained for field sizes > 44 cm2, whereas for field sizes  33 cm2, the TPS doses were overestimated by 3%-4% as compared to the literature data. Discussion: Challenges in TPS commissioning for small fields were highlighted by this study; it may be necessary to correct deviations in the TPS calculation for small segment sizes in the delivery of IMRT once such deviations are confirmed by careful measurements. Acknowledgments D. Followill, S. Kry, D. Thwaites, J. Povall, D. Georg, W. Lechner, M. Tenhunen, M. Tomsej, A. Carlsson Tedgren, M. Arib, W. Bulski, K. Chelminski, S. Luo, V. Alves, J. Samper, D. Ekendahl, R. B. Devu, S. Sirimanoroth, S. P. Vinatha. References: [1] Followill D.S. et al., The Radiological Physics Center’s standard datatset for small field size output factors, J. Appl. Clin. Med. Phys., vol. 13, Nr 5, 2012, p. 282-289 (erratum vol. 15, Nr 2, 2014, p. 356-357).

MULTIVARIATE STATISTICAL ANALYSIS OF FACTORS RELATED TO MEAN ANNUAL INDOOR RADON CONCENTRATIONS OF GREEK DWELLINGS Dimitrios Nikolopoulos a, Sofia Kottou b, Ermioni Petraki a,c, Efstratios Vogiannis d, Christos Michail e, Anna Louizi b, Yiannis Chaldeos a, Panayiotis H. Yannakopoulos a. a TEI of Piraeus, Department of Electronic Computer Systems Engineering, Petrou Ralli & Thivon 250, 12244, Aigaleo, Greece; b University of Athens, Medical School, Department of Medical Physics, Mikras Asias 75, 11527, Athens, Greece; c Brunel University, Department of Engineering and Design, Kingston Lane, Uxbridge, Middlesex UB8 3PH, London, UK; d Evangeliki Model School of Smyrna, Lesvou 4, 17123, Nea

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Smyrni, Greece; e TEI of Athens, Department of Biomedical Engineering, A.Spyridonos, 12210, Aigaleo, Greece Url:http://env-hum-comp-res.teipir.gr/ Between 1994 and 2000 a large scale radon survey was implemented in Greece with calibrated radon dosimeters based on CR-39 polymers. The dosimeters were exposed for a period of twelve-months. From the measured dwelling sample, 963 apartments were accompanied with fully filled questionnaires. The questionnaires were designed according to the international standards so as to account for factors that would potentially affect mean annual indoor radon concentrations. The available questionnaires were rechecked recently during 2012-14 with multivariate statistics in order to quantify possible inter-connections. Important factors were the following: i) area, ii) building levelfloor, iii) ground type, iv) basement, v) building type, vi) construction year, vii) building walls contact, viii) wall materials, ix) floor materials. Several multivariate methods were employed in the analysis, namely (i) Linear Regression Analysis, (ii) One way or multiway ANOVA, (iii) General MANOVA, (iv) Stepwise Regression Analysis and (v) Principal Components Analysis. As most significant, it was found that approximately 0.1% of the examined dwellings were associated with outlier radon concentrations. Significant were the statistical correlations between indoor measured mean annual indoor radon concentrations and ”building level-floor” factor, as well as ”wall materials” factor. The findings of this work provided weak evidence regarding potential association of the factors ”building type”, ”construction year” and “floor materials” with mean annual radon concentration. Minor was the link with ”building walls contact” factor. It is important to note, that the employed statistical methods provided significant different results for the relative efficiency of the investigated factors.

MODELING OF RADON AND PROGENY CONCENTRATION PEAKS IN THERMAL SPAS: RESULTS FROM THE SEMI-EMPIRICAL APPROACH FROM SEVERAL SPAS IN GREECE Dimitrios Nikolopoulos a, Efstratios Vogiannis b, Sofia Kottou c, Yiannis Chaldeos d, Ermioni Petraki a, e, Panayiotis H. Yannakopoulos a. a TEI of Piraeus, Department of Electronic Computer Systems Engineering, Petrou Ralli & Thivon 250, 12244, Aigaleo, Greece; b Evangeliki Model School of Smyrna, Lesvou 4, 17123, Nea Smyrni, Greece; c University of Athens, Medical School, Department of Medical Physics, Mikras Asias 75, 11527, Athens, Greece; d IEEE Student, TEI of Piraeus, Department of Electronic Computer Systems Engineering, Petrou Ralli & Thivon 250, 12244, Aigaleo, Greece; e Department of Engineering and Design, Brunel University, Kingston Lane, Uxbridge, Middlesex UB8 3PH, London, UK Url:http://env-hum-comp-res.teipir.gr/ Radon and its short progeny (218Po, 214Pb, 214Bi and 214Po) are important radioactive indoor air pollutants that are well recognised for their impact on humans. Thermal spas are indoor environments which are identified as significant sources of human radiation burden due to bathing and working. Especially the transient radon and progeny concentration peaks have gained scientific attention because these were associated with short-term impact in patients and personnel. Between 2007 and 2013, novel first-order modelling was achieved for the transient concentration peaks of both radon and progeny. This type of modelling is based on a dynamical set of first-order differential equations describing radon generation and decay. These equations are combined with measurements and several reference values constituting a so-called semiempirical approach. Real-data are used as model inputs. These are utilised through numerical modelling and the use of the Levenberg-Marquard method in estimating progeny concentrations in non-measured time moments. Through these, several exposure and dosimetric quantities are calculated. In this work, the model will be presented along with several verifications derived from the spas of Ikaria, Loutraki, and Lesvos Island (Greece). It worth to note that through this type of modelling several non-easily

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measured parameters -such as the attachment rate and deposition rate constants- are retrieved. Attachment rate constants ranged between 0.2 and 55 h-1. Deposition rate constants were found different between the short-lived radon decay, namely between 0.2 and 8 h-1 for attached nuclei and 0.4 and 64 h-1 for unattached nuclei. Mean annual effective doses range between 0.001 mSv and 0.6 mSv for patients and 0.001 mSv and 19 mSv for personnel. Differentiations were observed between the various spa centers depending on the radon potential of the thermal waters, the water entrance techniques, the building characteristics and other parameters.

RADON ENTRANCE AND ITS DAILY MOVEMENT INTO A CLOSED DETACHED OF THREE LEVEL HOUSE Efstratios Vogiannis a, Dimitrios Nikolopoulos b, Maria Koukou c, d, Sofia Kottou e, Michail Vrachopoulos c, d. a Evangeliki Model School of Smyrna, Lesvou 4, 17123, Nea Smyrni, Greece; b TEI of Piraeus, Department of Electronic Computer Systems Engineering, Petrou Ralli & Thivon 250, 12244, Aigaleo, Greece; c University of Applied Sciences, Mechanical Engineering Department, Energy and Environmental Research Laboratory, Central Greece 34400, Psachna, Evia, Greece; d Department of Mechanical Engineering, TEI of Halkis, 34400, Psachna, Evia, Greece; e Medical Physics Department, Medical School, University of Athens, Mikras Asias 75, 11527, Athens, Greece Url:http://env-hum-comp-res.teipir.gr/ An old house of three levels (ground floor, 1st and 2nd floor connected with internal stairs) was selected for the investigation of radon entrance and its daily movement among house levels. An Alpha Guard radon monitor was situated in the middle of each level. Continuous measurements were taken for a week period in 10 min intervals. Simultaneous measurements were taken for pressure, humidity and temperature, and also differences on pressure and temperature between house floors. Weather data also recorded during survey period. Measurement results were investigated for the purpose to discover the factors that affect radon entrance and movement through house levels. Main radon entrance indoors is the basement floor and secondary the building materials. This was due to the type of house selected, constructed from radon free materials, especially the upper floor. House remained closed during measurements to eliminate every other factor that affects radon movement. In the other hand the closed house ensured fixed air exchange rate which is the major factor that affects radon indoor concentration. Air driven forces due to differences in pressure and temperature were analysed in relation to outdoor air conditions. Weather conditions strongly affect radon entrance from basement. Indoor air gradually heated produces an upper stream known as chimney effect, drives radon from the floor working as vacuum. Movement from down to upper floor due to chimney effect was found not so strongly depended and it was probably due to high radon molecular weight. Radon concentrations in ground floor show a daily variation standard module. Peaks appeared when the previous described mechanism as vacuum amplifies the driven forces.

PRELIMINARY STUDY OF DISTRIBUTION OF INDOOR EMR IN GREEK DWELLINGS Sofia Kottou PhD Associate Professor a, Dimitrios Nikolopoulos PhD Associate Professor b, Dionysios Koulougliotis Professor c, Konstantinos Pouliezos MSc c, Efstratios Vogiannis PhD Director d, Nikolaos Gorgolis TEI Student b, Roxanne Suzzet Lorilla TEI Student c, Georgios Kefalas TEI Student c, Sotiria Potozi TEI Student c, Yiannis Chaldeos TEI Student b, Theodore Sevvos TEI Student b, Ermioni Petraki MSc, PhD candidate b, Christos Michail MSc, PhD d, Panayiotis Moustanis Assis. Professor e, Anastasios Kalimeris Assis. Professor c, Panayiotis H. Yannakopoulos PhD Professor b. a Medical Physics Department, Medical School, University of Athens, Mikras Asias 75, 11527, Athens, Greece;