Optimization of image quality and reduction of radiation dose in CT using Philips dose right tools

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Abstracts/Physica Medica 31 (2015) S15–S21

P.4 OCCUPATIONAL EXPOSURE OF RADIATION WORKERS AT GROOTE SCHUUR HOSPITAL T.C. Kotzé *, C.J. Trauernicht. Groote Schuur Hospital, Medical Physics Department, University of Cape Town, Cape Town, South Africa Introduction: The ICRP recommends that radiation workers should not receive more than 100 mSv over any 5 consecutive years, and not more than 50 mSv in any of those 5 years. The Directorate Radiation Control, Department of Health has adopted an occupational dose limit of 20 mSv per year. The aim of this study was to: • investigate all reported alleged occupational exposures of more than 4 mSv between November 2011 and March 2015; • determine the reason(s) for these exposures; and • determine high-risk areas. Materials and Methods: An Excel spreadsheet was developed which included all the dose records since November 2011. This enables the hospital to easily track the dose history of any radiation worker, observe trends in the dose history, and to investigate those exposures for which the hospital is not legally required to perform an investigation. The database currently consists of 18,500 dose records for 580 radiation workers. Results: A total of 31 alleged radiation over-exposures of more than 4 mSv were reported between November 2011 and March 2015, the highest value being 29.7 mSv for a single wearing period. A total of 41 exposures between 2 and 4 mSv and a total of 116 exposures between 1 and 2 mSv were reported during the same period. 84% of the alleged over-exposures came from staff working in interventional radiology. This is ascribed to the fact that the TLD was worn on the outside of the lead rubber apron. Conclusion: It is of utmost importance to regularly evaluate the occupational radiation exposures of all radiation workers in order to establish trends and identify possibly unsafe working conditions and/or practices. Utilizing an electronic occupational exposure database proved to be extremely useful in this regard at Groote Schuur Hospital. Keywords: Occupational exposure, Radiation worker, TLD

P.5 A BILATERAL COMPARISON OF LUTETIUM-177 ACTIVITY MEASUREMENTS

Conclusion: The NMISA secondary standard ionization chamber was calibrated for 177Lu during an international key comparison and used successfully during a bilateral comparison between ANSTO and NMISA. Keywords: Bilateral comparison, 177Lu solution, Secondary standard ionization chamber P.6 RADIATION ASPECTS RELATED TO HIGH AND LOW SPECIFIC ACTIVITY 177 LU AND ITS SIGNIFICANCE TO PEPTIDE RECEPTOR RADIATION THERAPY S. Maage *, O. Knoesen. NTP Radioisotopes SOC Ltd Introduction: Peptide receptor radiation therapy (PRRT) with Lutetium177 (177Lu) labelled to Dota-peptide carriers, e.g. Dotatate, is used for the treatment for various tumours. It is generally accepted that the maximum therapeutic effect for 177Lu-Dotatate at the treatment site is achieved with a specific activity of not less than 20Ci 177Lu/mg to maximise the 177Lu : Dotapeptide ratio. Non-carrier added 177Lu n.c.a. is produced indirectly by irradiating enriched ytterbium-176 (176Yb). Carrier-added 177Lu c.a. is produced directly by irradiating enriched 176Lu. Materials and Methods: Theoretical calculations were performed with FISPACT using SAFARI-1 reactor parameters. For the indirect route, calculations were performed for 1 g of 99.56% enriched 176Yb as Yb2O3, irradiated with a total neutron flux of 5.94E14 n/cm2/s for 6–14 days, followed by decay intervals for up to 14 days after the end of irradiation (EOI). Calculations for the direct route were for 100 μg of 82% enriched 176Lu as Lu(NO3)3 using identical parameters as for 177Lu n.c.a. Results: A comparison of the specific activities obtained for 6 and 14 day irradiation periods are 105.3 and 100.2Ci/mg for the indirect route and 19.5 and 27.8Ci/mg for the direct route after two days’ decay after EOI. After 14 days’ decay these values decrease to 93.4 and 80.4Ci/mg for the indirect route and 6.4 and 9.7Ci/mg for the direct route. The specific activity for 177Lu n.c.a. is at least 3.6 times higher than for 177Lu c.a. Furthermore, the 177m Lu : 177Lu is at least a factor of 1E+04 lower in 177Lu n.c.a. Conclusion: The indirect production route provides high specific activity 177 Lu n.c.a with the long-shelf life and minimal 177mLu, and is thus preferred for PRRT. Keywords: Specific activity, Lutetium-177, PRRT

J. Lubbe *, M.J. van Staden, B.R.S. Simpson, M.W. van Rooy. National Metrology Institute of South Africa, 15 Lower Hope Road, Rosebank, Cape Town 7700, South Africa

P.7 OPTIMIZATION OF IMAGE QUALITY AND REDUCTION OF RADIATION DOSE IN CT USING PHILIPS DOSE RIGHT TOOLS

Introduction: There has been increasing interest in the use of lutetium177, a beta-gamma emitter, for radionuclide-based radiotherapy for certain types of cancers. Recently the Australian Nuclear Science and Technology Organisation (ANSTO) requested the NMISA Radioactivity Standards Laboratory to participate in a bilateral comparison of 177Lu to check the uniformity of their activity measurements. The NMISA measurements were undertaken on a secondary standard ionization chamber (IC) using a calibration figure determined for 177Lu through absolute activity measurement. Materials and Methods: Absolute activity measurements of 177Lu were made at NMISA by the 4πβ-γ coincidence extrapolation technique using liquid scintillation counting. This standardized solution was used to verify the calibration figure (0.3179 ± 0.0028 pA/MBq) determined for the NMISA IC. During 2014 ANSTO sent NMISA an ampoule containing a solution of 177Lu for the bilateral comparison. The previously obtained calibration figure was used to determine the activity of 177Lu in the ampoule. Results: The accuracy of the absolute activity measurement was confirmed through participation in an international key comparison of 177Lu, the NMISA result comparing favorably with the comparison reference value. The inter-comparison results will be shown relative to those of the other participants, which included ANSTO. For the bilateral comparison with ANSTO, the Relative Degrees of Equivalence between ANSTO and NMISA were determined as −0.010 ± 0.016 (i.e. ANSTO lower by 1%). The degrees of equivalence between ANSTO and NMISA were in excellent agreement with those established during the 2009 international comparison.

N. Maphumulo *, H. Tlhapi. Department Medical Physics, Sefako Makgatho Health Sciences University, South Africa Introduction: The goal of clinical computed tomography (CT) scans is to produce images of high image quality for a more accurate image interpretation and diagnosis. However, an increase in CT image quality traditionally leads to a high radiation dose to the patient. The main limitations of reducing radiation dose associated with CT are the corresponding increase in image noise and the loss of spatial resolution which results in substantial deterioration of image quality. Recent developments have offered a solution to this problem based on image post-processing using iterative reconstruction algorithms. This study is aimed at determining the influence of iterative reconstruction on image quality and the potential of reducing patient dose associated with CT scans without substantial reduction in image quality. Materials and Methods: Materials used were Catphan 500, 128 slice Philips CT scan, IQWorks v0.7.2 image processing softwere, spirit level. The catphan 500 was scanned using the pelvis bony imaging protocol (KVp 120, mAs 60), helical scan and a pitch of 0.891. The acquired data were reconstructed using the standard filtered back projection and iterative reconstruction algorithms (IDose1, 2, 4, 5 and 7) and the images were compared. Results: Image Quality was quantified using Spatial Resolution (MTF50, MTF10 and FWHM from the point spread function), signal to noise ratio (SNR) and Noise. The result showed Improvement in image quality: with MTF10 and FWHM increasing by 10.2% and 9.4% respectively (spatial resolution), SNR increased by 123.83% and the noise was reduced by 55%.

Abstracts/Physica Medica 31 (2015) S15–S21

Conclusion: Iterative reconstruction proved to increase image quality by a substantial increase in SNR and a reduction in image noise. Keywords: Image quality, Radiology, CT

P.8 BREAST ENTRANCE EXPOSURE AND AVERAGE GLANDULAR DOSE: OBSERVER PERFORMANCE STUDY D Mashalane * ,a, H.L. Tlhapi b. a Department of Medical Physics, Sefako Makgatho Health Sciences University, Pretoria, South Africa; b Department of Diagnostic Radiology, Dr George Mukhari Academic Hospital, Pretoria, South Africa Introduction: The objective of this study was to measure the breast entrance exposure and to calculate the corresponding glandular dose for an average patient with approximately 4.5 cm compressed breast thickness of 50% adipose. Materials and Methods: The materials used included a Selenia Lorad digital mammogram machine, phantom of 4.5 cm thickness, a 24 × 30 cm compression paddle with a compression device and a PTW ionisation chamber. The ACR Phantom was centred laterally on the image receptor and it was positioned such that the chest wall edge of the phantom was aligned with the chest wall edge of the image receptor. The ionisation chamber was positioned in the X-ray field besides the ACR phantom, centred 4.0 cm in from the chest wall of the image receptor and the centre of the chamber levelled with the top surface of the ACR phantom. The compression paddle was placed above the phantom and chamber to achieve a compression thickness of 4.5 cm. The system was set in the AEC mode, with the compensation step of 0 and AEC sensor position 2. Large focal spot was selected with molybdenum filter and 28 kVp. Results: Four exposure measurements were taken for analysis: 2.37 mGy, 2.37 mGy, 2.41 mGy and 2.40 mGy, and the standard deviation of 0.0016 was obtained yielding a covariance of 0.01. The average glandular dose was calculated using the equation: AGD = f × r and it was 0.39 mGy. Conclusion: This study was done according to the manufacturer’s specifications of the dose measurements in mammography units. The results were within the recommended criteria for imaging an average breast. Keywords: Mammography, Glandular dose, Compression paddle, ACR phantom

P.9 CONCRETE DENSITY ESTIMATION OF GROOTE SCHUUR HOSPITAL LINEAR ACCELERATOR BUNKER WALLS USING IMPACT ECHO TESTING F. Moosa *,a, H. Burger b, C. Trauernicht b, G. Blassoplesc c, E. Okwori d, B. Nyoni d, P. Moyo d. a Department of Medical Physics, Groote Schuur Hospital; b Department of Medical Physics, Groote Schuur Hospital and University of Cape Town; c KFD Wilkinson Consulting Engineers, Cape Town; d Department of Civil Engineering, University of Cape Town Introduction: Groote Schuur Hospital constructed a new radiotherapy bunker for a high-energy linear accelerator. During construction areas of honeycombing became evident in the concrete. Honeycombing reduces the density of concrete and may affect the shielding integrity of the walls. Since the linac had not yet been installed, the radiation beam could not be used for testing, and an alternative non-destructive testing method had to be employed. The aim of this study was to use the impact-echo technique to verify the wall integrity. Materials and Methods: In this method, a mechanical impact is used to create stress waves, which propagate through the concrete and are reflected or refracted where there are changes in material characteristics such as density. In theory, non-visible honeycombing at depth will present multiple reflection surfaces and should result in a broad-band response with multiple small peaks. The propagation of the stress wave is dependent on the elastic modulus, density and Poisson’s ratio of the material. Radiation measurements at the same positions on the walls where impact echo testing was performed will be completed with the 6 MV linear accelerator once installed, and the data extrapolated for 18 MV photon beams as per bunker design.

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Results: The impact echo results show that the density of the primary barriers ranged from 2.30 g/cc to 2.55 g/cc for the one wall, and from 2.20 g/ cc to 2.45 g/cc for the other primary barrier. However, testing showed a possible localised void in one of the walls. Core drilling at that point to a depth of 1 m showed no evidence of a void. Conclusion: The final results on whether the primary walls offer adequate shielding will only be confirmed once the linear accelerator is functional. The impact-echo testing results and radiation survey results will be correlated. Keywords: Impact-echo, Shielding, Honeycombing, Radiotherapy, Non-destructive P.10 COMPARISON OF TWO DIFFERENT CELL CYCLE PROLIFERATION ANALYSIS METHODS USING BrdU X. Muller *, J. Slabbert. Department Radiation Biophysics, NRF-iThemba LABS, Somerset West, South Africa Introduction: The extent of cellular radiation damage is dependent on the stage of the cell cycle and new methods to determine this are frequently being developed. Here we used bromodeoxyuridine (BrdU) that is incorporated into newly synthesized DNA and is detected using an immunofluorescent anti-body. This method aims to quantify the fraction of cells in S-phase as BrdU acts as a thymidine analogue. The advantages of using BrdU are that it allows for the identification and analysis of actively cycling cell fractions and also permits the determination of cell cycle kinetics. The aim of this study was to compare S-phase fractions observed using flow cytometry with microscopy methods. Materials and Methods: Isolated lymphocytes were given 0 Gy and 2 Gy doses of cobalt-60 gamma rays. PHA stimulated cells were cultivated for 45 hours and then either pulse labelled for 15 minutes or incubated for 1 hr in medium containing BrdU. Non-stimulated lymphocytes were labelled concurrently and used as negative controls. Counterstaining using a BrdU antibody was done using separate protocols for flow cytometry and microscopy. Results: A slightly higher percentage of S-phase fractions could be detected using flow cytometry (23% for 15 minute and 33% for 1 hour labelling) compared to microscopy analysis 21% for 15 minute and 30% for 1 hour labelling). Conclusion: Flow cytometry is the preferred method to quantify S-phase cell fractions. Microscopy based analysis is more tedious and has a greater risk of human error. Keywords: Bromodeoxyuridine, S-phase, Cell cycle kinetics P.11 POTENTIAL RADIOSENSITISATION OF BREAST- AND LUNG CANCER CELLS BY A NOVEL ANTI-MITOTIC OESTRONE ANALOGUE E.M. Nolte *,a, R. Lakier b, A. Van Rensburg b, J.M. Helena a, M. Verwey a, A.M. Joubert a, A.E. Theron a. a Department of Physiology, Faculty of Health Sciences, University of Pretoria, Pretoria, South Africa; b Department of Radiation Oncology, Steve Biko Academic Hospital, Faculty of Health Sciences, University of Pretoria, Pretoria, South Africa Introduction: Breast- and lung cancers are among the most frequently diagnosed cancer types in South Africa. 2-Methoxyestradiol was reported to sensitise prostate cancer cells to radiation therapy. The aim of this in vitro study was to determine whether a low dose of an in silico designed 2ME analogue 2-ethyl-3-O-sulphamoyl-estra-1,3,5(10),15-tetraen-17-ol (ESE15-ol) pre-exposure increases the sensitivity of breast- and lung cancer cells to γ-radiation. Methods and Materials: Dose–response curves using Annexin-FITC were used to determine the concentration of drug and dose of γ-radiation at which apoptosis was first detected. Morphological studies included light- and transmission electron microscopy. Clonogenic studies were done by allowing colony formation for 7 days after radiation. Flow cytometry was used for apoptosis detection, cell cycle analysis, Bcl-2 signalling effects, as well as reactive oxygen species production (superoxide). Effects on epigenetics were determined by flow cytometry analysis of histone deacetylase (HDAC) 1