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P11. Dose verification for high-dose bulk industrial 60Co irradiators with chemical dosimeters and gafchromic media
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Abstracts / Physica Medica 32 (2016) 161–167
P10. Radiosensitization of breast adenocarcinoma cells by a novel estrone analogue is dependent on reactive oxygen species signalling M. Verwey a, A.M. Joubert a, W. Meijer a, E.M. Nolte a, R. Lakier b, M. Etsebeth b, J. Helena 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 and aim. The novel antimitotic drug 2-ethyl-3-O-sul pamoyl-estra-1,3,5(10),15-tetraen-17-ol (ESE-15-ol) is an in silicodesigned 17-b-estradiol analogue that induces apoptosis and disregulates autophagy in various neoplastic cell lines. The compound alters microtubule dynamics inducing both intrinsic and extrinsic death pathways. The hypothesis was formed that pre-exposure to the compound would sensitize breast adenocarcinoma (MDA-MB231) cells to gamma radiation, in pathways dependent on reactive oxygen species (ROS) generation. Methods and materials. The hypothesis was tested by inhibiting ROS formation with N-acetyl-cysteine (NAC). The half-maximal growth-inhibitory concentration (IG50 Þ of ESE-15-ol after 24 h was determined with and without NAC via spectrophotometric quantification of crystal violet. MDA-MB-231 cells were presensitized with half the IG50 concentrations prior to 6 Gy radiation. Morphological studies were done using polarized-optical transmitted light differential interference light microscopy and confocal microscopy using anti-a tubulin antibodies and MitotrackerÒ mitochondrial staining. Quantitative studies were completed using flow cytometry to detect apoptosis induction, loss of mitochondrial membrane potential and reactive oxygen species production, as well as to analyze cell cycle progression and mitochondrial signal transduction pathways. Results. The IG50 of ESE-15-ol was determined at a concentration of 0.18 lM after a 24-h exposure. Results obtained from the morphological studies indicated that incubation with NAC reduced apoptotic cell death despite microtubule depolarization after ESE-15-ol presensitization prior to gamma radiation. Flow cytometric quantification indicated a reduction in apoptosis, mitochondrial membrane depolarization, as well as in reactive oxygen species when samples were concurrently undergoing antioxidant treatment. Conclusion. This in vitro study revealed that inhibition of reactive oxygen species signalling resulted in a decreased effectiveness of ESE-15-ol to presensitize MDA-MB-231 cells to gamma radiation. Thus the hypothesis was accepted. Further quantification of ROS on autophagy induction, as well as its role in the radiosensitization mechanisms, will be carried out in vitro and in vivo. http://dx.doi.org/10.1016/j.ejmp.2016.07.077
P11. Dose verification for high-dose bulk industrial 60Co irradiators with chemical dosimeters and gafchromic media P. Beukes a, M. Moller b, G. Munhenga c, J.P. Slabbert a a Radiation Biophysics Division, NRF iThemba LABS, Cape Town, South Africa b Department of Medical Physics, University of the Free State, Bloemfontein, South Africa c Centre for Opportunistic, Tropical and Hospital Infections, National Institute for Communicable Disease, Johannesburg, South Africa Introduction. Dosimetry and dose verification at bulk industrial irradiator facilities is subject to numerous challenges, most notably due to their high volume, high throughput design and operations. Industries such as the Sterile Insect Technique (SIT), a biological control practice for the management of insect pests of agricultural and
medical or veterinary significance, rely on annually derived output factors to deliver sterilization doses to organisms within strict parameters. Routine dose verification should therefore constitute an integral part of the quality control system. Materials and methods. Two distinct dosimeter types were employed in this study. Firstly a chemical solution, Fricke’s solution made up of 1 mM Fe(NH4)2(SO4)2, 0.8 N H2 SO4 , 1 mM NaCl high purity chemicals, decanted in 2 ml ampules, secondly enveloped 1 cm2 EBT2 radiochromic media sections. Dosimeters were exposed in a reference 60Co field under charged particle equilibrium conditions to incremental doses up to 100 Gy. Dosimeter absorbance measurements were conducted with a diode array spectrophotometer, resolution of 1 nm, at 304 nm and 676 nm for the Fricke and EBT2 dosimeters respectively. Results. Dosimeter absorbance unit (AU) readings for the Fricke (0.06–0.35) and EBT2 (0.05–1.36) dosimetry systems were recorded for the dose range 0–100 Gy. Linear dose response relationships were noted for both the Fricke (dose range 20–100 Gy, r2 ¼ 0:9992) and EBT2 (2–100 Gy, r2 ¼ 0:9868) dosimetry systems. The dose–response relationship of the Fricke dosimetry system (3:6 103 2:42 105 ) is roughly one order of magnitude lower compared to the EBT2 (1:35 102 3:67 104 ) system. Conclusion. Both dosimetry systems prove to be reliable dose verification tools for bulk industrial irradiator applications. The Fricke dosimetry system, a primary dosimeter, remains the preferred dosimeter due to its superior linear dose response and higher dose range capabilities. http://dx.doi.org/10.1016/j.ejmp.2016.07.078
P12. Comparison between impact echo test results and radiation survey of the primary barrier of a radiotherapy bunker F. Moosa a, H. Burger b, H. Fourie a, C. Trauernicht b, G. Blassoples c, E. Okwori d, B. Nyoni d, P. Moyo d a Department of Medical Physics, Groote Schuur Hospital, South Africa b Department of Medical Physics, Groote Schuur Hospital and University of Cape Town, South Africa c KFD Wilkinson Consulting Engineers, Cape Town, South Africa d Department of Civil Engineering, University of Cape Town, South Africa 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 is to compare the results from the impact echo testing with the radiation survey results. Materials and methods. In impact echo testing, 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 were done with the 6 MV linear accelerator during its safety survey, and the data was extrapolated for an 18 MV photon beam as per bunker design. Results. The impact echo results show that the density of the primary barrier ranged from 2.30 g/cc to 2.55 g/cc for the primary shielding wall adjacent to the maze (the other one is underground).
Abstracts / Physica Medica 32 (2016) 161–167
P10. Radiosensitization of breast adenocarcinoma cells by a novel estrone analogue is dependent on reactive oxygen species signalling M. Verwey a, A.M. Joubert a, W. Meijer a, E.M. Nolte a, R. Lakier b, M. Etsebeth b, J. Helena 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 and aim. The novel antimitotic drug 2-ethyl-3-O-sul pamoyl-estra-1,3,5(10),15-tetraen-17-ol (ESE-15-ol) is an in silicodesigned 17-b-estradiol analogue that induces apoptosis and disregulates autophagy in various neoplastic cell lines. The compound alters microtubule dynamics inducing both intrinsic and extrinsic death pathways. The hypothesis was formed that pre-exposure to the compound would sensitize breast adenocarcinoma (MDA-MB231) cells to gamma radiation, in pathways dependent on reactive oxygen species (ROS) generation. Methods and materials. The hypothesis was tested by inhibiting ROS formation with N-acetyl-cysteine (NAC). The half-maximal growth-inhibitory concentration (IG50 Þ of ESE-15-ol after 24 h was determined with and without NAC via spectrophotometric quantification of crystal violet. MDA-MB-231 cells were presensitized with half the IG50 concentrations prior to 6 Gy radiation. Morphological studies were done using polarized-optical transmitted light differential interference light microscopy and confocal microscopy using anti-a tubulin antibodies and MitotrackerÒ mitochondrial staining. Quantitative studies were completed using flow cytometry to detect apoptosis induction, loss of mitochondrial membrane potential and reactive oxygen species production, as well as to analyze cell cycle progression and mitochondrial signal transduction pathways. Results. The IG50 of ESE-15-ol was determined at a concentration of 0.18 lM after a 24-h exposure. Results obtained from the morphological studies indicated that incubation with NAC reduced apoptotic cell death despite microtubule depolarization after ESE-15-ol presensitization prior to gamma radiation. Flow cytometric quantification indicated a reduction in apoptosis, mitochondrial membrane depolarization, as well as in reactive oxygen species when samples were concurrently undergoing antioxidant treatment. Conclusion. This in vitro study revealed that inhibition of reactive oxygen species signalling resulted in a decreased effectiveness of ESE-15-ol to presensitize MDA-MB-231 cells to gamma radiation. Thus the hypothesis was accepted. Further quantification of ROS on autophagy induction, as well as its role in the radiosensitization mechanisms, will be carried out in vitro and in vivo. http://dx.doi.org/10.1016/j.ejmp.2016.07.077
P11. Dose verification for high-dose bulk industrial 60Co irradiators with chemical dosimeters and gafchromic media P. Beukes a, M. Moller b, G. Munhenga c, J.P. Slabbert a a Radiation Biophysics Division, NRF iThemba LABS, Cape Town, South Africa b Department of Medical Physics, University of the Free State, Bloemfontein, South Africa c Centre for Opportunistic, Tropical and Hospital Infections, National Institute for Communicable Disease, Johannesburg, South Africa Introduction. Dosimetry and dose verification at bulk industrial irradiator facilities is subject to numerous challenges, most notably due to their high volume, high throughput design and operations. Industries such as the Sterile Insect Technique (SIT), a biological control practice for the management of insect pests of agricultural and
medical or veterinary significance, rely on annually derived output factors to deliver sterilization doses to organisms within strict parameters. Routine dose verification should therefore constitute an integral part of the quality control system. Materials and methods. Two distinct dosimeter types were employed in this study. Firstly a chemical solution, Fricke’s solution made up of 1 mM Fe(NH4)2(SO4)2, 0.8 N H2 SO4 , 1 mM NaCl high purity chemicals, decanted in 2 ml ampules, secondly enveloped 1 cm2 EBT2 radiochromic media sections. Dosimeters were exposed in a reference 60Co field under charged particle equilibrium conditions to incremental doses up to 100 Gy. Dosimeter absorbance measurements were conducted with a diode array spectrophotometer, resolution of 1 nm, at 304 nm and 676 nm for the Fricke and EBT2 dosimeters respectively. Results. Dosimeter absorbance unit (AU) readings for the Fricke (0.06–0.35) and EBT2 (0.05–1.36) dosimetry systems were recorded for the dose range 0–100 Gy. Linear dose response relationships were noted for both the Fricke (dose range 20–100 Gy, r2 ¼ 0:9992) and EBT2 (2–100 Gy, r2 ¼ 0:9868) dosimetry systems. The dose–response relationship of the Fricke dosimetry system (3:6 103 2:42 105 ) is roughly one order of magnitude lower compared to the EBT2 (1:35 102 3:67 104 ) system. Conclusion. Both dosimetry systems prove to be reliable dose verification tools for bulk industrial irradiator applications. The Fricke dosimetry system, a primary dosimeter, remains the preferred dosimeter due to its superior linear dose response and higher dose range capabilities. http://dx.doi.org/10.1016/j.ejmp.2016.07.078
P12. Comparison between impact echo test results and radiation survey of the primary barrier of a radiotherapy bunker F. Moosa a, H. Burger b, H. Fourie a, C. Trauernicht b, G. Blassoples c, E. Okwori d, B. Nyoni d, P. Moyo d a Department of Medical Physics, Groote Schuur Hospital, South Africa b Department of Medical Physics, Groote Schuur Hospital and University of Cape Town, South Africa c KFD Wilkinson Consulting Engineers, Cape Town, South Africa d Department of Civil Engineering, University of Cape Town, South Africa 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 is to compare the results from the impact echo testing with the radiation survey results. Materials and methods. In impact echo testing, 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 were done with the 6 MV linear accelerator during its safety survey, and the data was extrapolated for an 18 MV photon beam as per bunker design. Results. The impact echo results show that the density of the primary barrier ranged from 2.30 g/cc to 2.55 g/cc for the primary shielding wall adjacent to the maze (the other one is underground).