- Email: [email protected]
Cancer radiation therapy: Quo Vadis?
e78
Abstracts / Physica Medica 30 (2014) e75ee121
Methods and Materials: ArraySL-4 is a commercially available, solid-state, 4x4 array detector covering an active area of 13.4mm2. Each pixel has 4774 square microcells connected in parallel, with individual cell side equal to 35um. GAGG:Ce scintillator array used in this study were purchased by Furukawa Co Ltd [3]. The reflector material used in the array is BaSO4 with 0.1mm thickness. GAGG:Ce scintillator is non hygroscopic, has good light yield (46000 ph/MeV) with peak emission at 530nm. Moreover, GAGG:Ce does not contain natural radioactivity, since it does not uses Lu. The density of GAGG:Ce is 6.63 g/cm3, with effective atomic number equal to 54.4 [4-6]. A symmetric resistive voltage division matrix was applied, which reduces the 16 outputs of the array to 4 position signals [6-7]. A Field Programmable Gate Array (FPGA) Spartan 6 LX150T was used for triggering and signal processing of the signal pulses acquired using a free running sampling technique [8]. Results: A raw image and the horizontal profile of one raw of the 6x6 GAGG:Ce scintillator array produced under 511keV excitation are shown in figure 1. The mean peak to valleys ratio is 40 (std¼8.2).
Fig. 1. Raw image of the 6x6 GAGG:Ce scintillator array and a horizontal profile of the central scintillator elements produced under 511keV excitation. Scintillator array is coupled with optical grease (BC-630).
Energy spectra obtained with two different radioactive sources from a single 3x3x5mm3 GAGG:Ce scintillator element (red square on raw image) are shown in figure 2. The mean energy resolution for the GAGG:Ce array was calculated equal to 10.5% (std¼0.44) and 9% (std¼0.63) under 511keV and 662keV irradiation using Gaussian fit within a +/-10% energy window centered around the photopeak.
could be an interesting application using the aforementioned GAGG/ SIPM array detector. In such a dual SPECT/PET detector module, proper mechanical insert of the collimator, as well as the adjustment of the SiPMs array bias voltage and the gain amplification of the position signals have to be properly controlled to allow transition from PET to SPECT mode. Acknowledgment: This research has been co-funded by the European Union (European Social Fund) and Greek national resources under the framework of the “Archimedes III: Funding of Research Groups in TEI of Athens” project of the “Education & Lifelong Learning” Operational Program. References: C. Piemonte et al. ”Recent developments on silicon photomultipliers produced at FBK-irst ,” IEEE Nucl. Sci. Symp. Conf. Rec: pp. 2089e2092, 2007. H. S. Yoon et. al. ”Initial results of simultaneous PET/MRI experiments with an MRI-compatible silicon photomultiplier PET scanner,” J.N.M, vol. 53, pp. 608, 2012 Available online at: http://www.furukawakk.co.jp/e_index.htm J. Iwanowska et al. ”Performance of cerium-doped Gd3Al2Ga3O12 (GAGG:Ce) scintillator,” Nucl. Instr. and Meth. Phys. Res. A, vol. 712, pp. 3440, 2013. S. Yamamoto et al. ”Development of an ultrahigh-resolution Si-PM-based dual-head GAGG coincidence imaging system,” Nucl. Instr. and Meth. Phys. Res. A, vol. 703, pp.183-189, 2013. S. David et al. ”Comparison of three Resistor Network Division Circuits for the readout of 4x4 Pixel SiPM Arrays,” Nucl. Instr. Meth. Phys. Res. A, vol. 702, pp. 121e125, 2013. V. Popov et al. ”A novel readout concept for multianode photomultiplier tubes with pad matrix anode layout,” Nucl. Instrum. Meth. A, vol 567, pp. 319, 2006. M. Streun, G. Brandenburg, H. Larue, E. Zimmermann, K. Ziemons and H. Halling, ”Pulse Recording by Free-Running Sampling,” IEEE Trans. Nucl. Sci. vol.48, pp. 524, 2001. M. Georgiou, S. David, E. Fysikopoulos and G. Loudos ”Development of a SIPM based gamma-ray imager using a Gd3Al2Ga3O12:Ce (GAGG:Ce) scintillator array,” IEEE Nucl. Sci. Symp.& Med. Imag conf. M21-48, Oct 27- Nov 2, Seoul, Korea, 2013. CANCER RADIATION THERAPY: QUO VADIS? Мersini Мakropoulou. Physics Department, School of Applied Mathematical and Physical Sciences, National Technical University of Athens, Greece
Fig. 2. Energy spectra of a central scintillator element of the GAGG:Ce array under 22 Na and 137Cs irradiation.
Discussion e Conclusion: The acquired raw image of the GAGG:Ce crystal array under 511keV excitation shows a clear visualization of all (6x6) discrete scintillator elements with a mean peak to valley ratio equal to 40. The mean energy resolution was measured equal to 10.5% and 9% respectively under 511keV and 662keV irradiation. Taking into account the results conducted in a previous study of our group [9] under low energy isotopes i.e. 57Co and 99mTc (for SPECT applications) using the same detector module materials, (mean energy resolution equal to 16.1±0.52% at 140keV and 18.1±0.64% at 122.1keV with high peak to valley ratio above to17) a SPECT/PET hybrid detector
In oncology, treating cancer with a beam of photons is a well established therapeutic technique, developed over 100 years, and today over 50% of cancer patients will undergo traditional X-ray radiotherapy. However, ionizing radiation therapy is not the only option, as the highenergy photons releasing their energy into cancerous tumor can lead to significant damage to healthy tissues surrounding the tumor. Therefore, in nowadays, advances in ionizing radiation therapy are competitive to non-ionizing ones. For example, photodynamic therapy (PDT) is another type of cancer treatment that uses laser light to destroy tumors. Apart of PDT, laser light can be used to remove cancer or precancerous tumors or to relieve symptoms of cancer, such as bleeding or obstruction. In PDT, a photosensitizer is injected into a patient and distributed all over the patient’s body. After a couple of days, the photosensitizer is accumulated selectively in cancer cells. Laser light is then used to activate the agent and destroy cancer cells, in the presence of cellular oxygen. PDT is a non-invasive or minimally invasive therapeutic procedure (through flexible endoscopes). The use of minimally invasive techniques in the management of patients represents a very interesting treatment option. Moreover, as the major breakthrough in cancer management is the individualized patient treatment, new biophotonic techniques, e.g. photo-activated drug carriers, help the improvement of treatment efficacy and/or normal tissue toxicity. Additionally, recent studies support that lasers could ameliorate cancer proton therapy. It is reported that laser-driven proton acceleration offers a significantly cheaper and relatively convenient approach to generate a beam of protons and experiments in this direction indicate that protons in laser proton therapy (LPT) kill cancer cells as effectively as those from accelerators. Although the biophysical
Abstracts / Physica Medica 30 (2014) e75ee121
studies for laser-driven ion acceleration are still in their infancy, very promising radiobiological processes are reported, since protons and photons have a parallel destructive effect on the DNA of the targeted tumor cells. In this work we will present the laser-based future objectives for cancer radiation therapy, aiming to address the relevant advances in the ionizing and non-ionizing radiation therapy, i.e. protons and heavy ions therapy, as well as photodynamic targeted and molecular therapies.
THE CONTRIBUTION OF DIFFUSION TENSOR IMAGING AND MAGNETIC RESONANCE SPECTROSCOPY FOR THE DIFFERENTIATION OF BREAST LESIONS AT 3T Ioannis Tsougos a, Patricia Svolos a, Evanthia Kousi e, Evangelos Athanassiou b, Kiriaki Theodorou a, Dimitrios Arvanitis d, Ioannis Fezoulidis c, Katerina Vassiou c,d. a Department of Medical Physics, Medical School, University of Thessaly, Biopolis, Larissa, Greece; b Department of Surgery, Medical School, University of Thessaly, Biopolis, Larissa, Greece; c Department of Diagnostic Radiology, Medical School, University of Thessaly, Biopolis, Larissa, Greece; d Department of Anatomy-HistologyEmbryology, University of Thessaly Medical School, Larissa, Greece; e CR-UK and EPSRC Cancer Imaging Centre, Royal Marsden Hospital, Sutton, Surrey, United Kingdom Background: Conventional breast magnetic resonance imaging (c-MRI) combined with dynamic contrast-enhanced MR mammography (DCEMRM), constitute a powerful diagnostic strategy for screening breast lesions. Nevertheless, the high sensitivity of c-MRI and DCE-MRM comes with low specificity that may lead to ambiguous diagnosis and unnecessary biopsies [1,2]. Molecular MR imaging, such as proton MR spectroscopy (1H-MRS) or diffusion-weighted imaging (DWI)/diffusion tensor imaging (DTI), has shown promise as a complementary tool to improve MR specificity and explore the underlying biological characteristic of tumors, going a step further from c-MRI. Purpose: The purpose of the current study was to investigate whether the combination of 1H-MRS and DTI metrics further contribute to the determination of breast lesion’s aggressiveness. Materials and methods: Fifty-one women with known breast abnormalities from conventional imaging were examined on a 3T MR scanner. DTI was performed during breast MRI, and fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured in the breast lesions and the contralateral normal breast. FA and ADC were compared between malignant lesions, benign lesions, and normal tissue. 1H-MRS was performed after gadolinium administration and choline peak was qualitatively evaluated. Results: In the present study 1H-MRS showed a sensitivity of 93.5%, specificity 80%, and accuracy 88.2%. Choline detection dependence on tumor size was observed. FA was significantly higher in breast carcinomas compared to benign lesions (0.24±0.05 and 0.21±0.04, respectively). Mean ADC value was lower for malignant tumors, however no significant difference was observed. The combination of Cho presence and FA achieved higher levels of accuracy (90.3%) and specificity (84%) in discriminating malignant from benign lesions over Cho presence or FA alone. This correlation between Cho and FA may be explained based on two factors: (a) Cho is associated with active cell proliferation and (b) tumor growth, results in higher cell density, which might cause water molecules to diffuse with a higher degree of directionality, in contrast to benign lesions. Conclusion: In conclusion, applying DTI and 1H-MRS together, adds incremental diagnostic value in the characterization of breast lesions and may sufficiently improve the low specificity of conventional breast MRI. References: 1. Orel SG et al. MR imaging of the breast for the detection, diagnosis, and staging of breast cancer. Radiology 2001; 220: 13e30. 2. Yen Y et al. Dynamic breast MRI with spiral trajectories: 3D versus 2D. J Magn Reson Imaging 2000; 11: 351-9.
e79
CHARACTERIZATION OF OCCUPATIONAL EMF EXPOSURE TO MRI SYSTEMS E. Karabetsos a, N. Skamnakis a, G. Gourzoulidis b, P. Sandylos c, Chryssa Paraskevopoulou c, T.G. Maris d, A. Xristodoulou e. a Greek Atomic Energy Commission, Non-Ionizing Radiation Office, Greece; b Physical Agents Determination Department, ΚYАЕ (COHS), Ministry of Labor, Greece; c Ygeia Hospital; d Assistant Professor of Medical Physics, Medical Department, University of Crete, Greece; e General Director of Health & Safety at Workplace, Ministry of Labor, Greece European legislation concerning the protection of workers from exposure to EMF was recently completed by directive 2013/35/ЕU (26.6.2013), the transposition of which to the national legislations should have been concluded by July 2016. This directive is a specific one of the framework directive 89/391/EEC and is part of the overall legislation for Health and Safety of Workers (HSW). MRI systems have played a key role, both to the postponement of the former 2004/40 EMF directive and to the formation of the latest ICNIRP guidelines adopted by the new directive. On the other hand, MRI systems are associated with the exposure of personnel to various frequencies and modulations, arousing peculiar safety issues. It is important to stress out that directive 2013/35/EU excludes, under a prescribed scheme, MRI systems from the application of the exposure limits values (ELVs). In the framework of this derogation, increased surveillance is applied, meaning that the basic issues of HSW are of key importance. In order for this increased surveillance to apply to workers and as part of the risk assessment procedure, the knowledge of the exact occupational exposure levels and scenarios is highly important. Normally the MRI operator does not enter the examination room during the MRI scan, but in some cases this is possible. Measurements of the magnetic and electromagnetic fields were performed during the MRI scans, next to the examination bed and at the operation console. Different MRI systems (1,5 and 3T) have been chosen for measurements in order to access occupational exposure compared to the limit values given by the directive and to the main principles of HSW. Low frequency exposures resulting from the function of the gradients of the MRI system (rectangular pulses at the kHz region), as well as high frequency exposures due to the application of the main RF frequency (pulses in sinx/x envelope at the MHz region), were measured. One of the most important aspects of this work, was associated with the post-processing of the measured EMF signals in order to be comparable to the action level (AL) values of the directive. Keywords: electromagnetic fields, MRI occupational exposure, risk assessment, Health and Safety of Workers.
IMPROVEMENT OF DOSE DISTRIBUTION WITH IRREGULAR SURFACE COMPENSATOR IN WHOLE BRAIN RADIOTHERAPY Hideki Fujita, Nao Kuwahata, Hiroyuki Hattori, Hiroshi Kinoshita, Haruyuki Fukuda. Department of Radiation Oncology, Osaka Saiseikai Nakatsu Hospital, Osaka, Japan The aim of this study was to evaluate the dosimetries of whole brain radiotherapy (WBRT) using irregular surface compensator (ISC) compare with conventional radiotherapy. The ISC involves modulation of the beam with the multileaf collimator (MLC), and increases the dose homogeneity to the target volume while decrease the absorbed dose in irradiated tissues outside the targeted tissue. Treatment plans were produced for 10 patients. All treatments were carried out with 10 MV photon energy from a Clinac iX with 120 MLC (Varian Medical Systems, Palo Alto, CA, USA). The prescription dose was 30 Gy in 10 fractions at the isocenter. With Eclipse treatment planning system (Varian Medical Systems), the anisotropic analytical algorithm was used for the dose calculation. The tissue heterogeneity correction was used in all the treatment plans. For ISC, the skin flash tool application was used to extend the optimal fluence. These two treatment plans were compared in terms of does in the planning target volume (PTV), the dose homogeneity index (DHI), the maximum doses, eye and lens doses and the monitor unit (MU) counts
Abstracts / Physica Medica 30 (2014) e75ee121
Methods and Materials: ArraySL-4 is a commercially available, solid-state, 4x4 array detector covering an active area of 13.4mm2. Each pixel has 4774 square microcells connected in parallel, with individual cell side equal to 35um. GAGG:Ce scintillator array used in this study were purchased by Furukawa Co Ltd [3]. The reflector material used in the array is BaSO4 with 0.1mm thickness. GAGG:Ce scintillator is non hygroscopic, has good light yield (46000 ph/MeV) with peak emission at 530nm. Moreover, GAGG:Ce does not contain natural radioactivity, since it does not uses Lu. The density of GAGG:Ce is 6.63 g/cm3, with effective atomic number equal to 54.4 [4-6]. A symmetric resistive voltage division matrix was applied, which reduces the 16 outputs of the array to 4 position signals [6-7]. A Field Programmable Gate Array (FPGA) Spartan 6 LX150T was used for triggering and signal processing of the signal pulses acquired using a free running sampling technique [8]. Results: A raw image and the horizontal profile of one raw of the 6x6 GAGG:Ce scintillator array produced under 511keV excitation are shown in figure 1. The mean peak to valleys ratio is 40 (std¼8.2).
Fig. 1. Raw image of the 6x6 GAGG:Ce scintillator array and a horizontal profile of the central scintillator elements produced under 511keV excitation. Scintillator array is coupled with optical grease (BC-630).
Energy spectra obtained with two different radioactive sources from a single 3x3x5mm3 GAGG:Ce scintillator element (red square on raw image) are shown in figure 2. The mean energy resolution for the GAGG:Ce array was calculated equal to 10.5% (std¼0.44) and 9% (std¼0.63) under 511keV and 662keV irradiation using Gaussian fit within a +/-10% energy window centered around the photopeak.
could be an interesting application using the aforementioned GAGG/ SIPM array detector. In such a dual SPECT/PET detector module, proper mechanical insert of the collimator, as well as the adjustment of the SiPMs array bias voltage and the gain amplification of the position signals have to be properly controlled to allow transition from PET to SPECT mode. Acknowledgment: This research has been co-funded by the European Union (European Social Fund) and Greek national resources under the framework of the “Archimedes III: Funding of Research Groups in TEI of Athens” project of the “Education & Lifelong Learning” Operational Program. References: C. Piemonte et al. ”Recent developments on silicon photomultipliers produced at FBK-irst ,” IEEE Nucl. Sci. Symp. Conf. Rec: pp. 2089e2092, 2007. H. S. Yoon et. al. ”Initial results of simultaneous PET/MRI experiments with an MRI-compatible silicon photomultiplier PET scanner,” J.N.M, vol. 53, pp. 608, 2012 Available online at: http://www.furukawakk.co.jp/e_index.htm J. Iwanowska et al. ”Performance of cerium-doped Gd3Al2Ga3O12 (GAGG:Ce) scintillator,” Nucl. Instr. and Meth. Phys. Res. A, vol. 712, pp. 3440, 2013. S. Yamamoto et al. ”Development of an ultrahigh-resolution Si-PM-based dual-head GAGG coincidence imaging system,” Nucl. Instr. and Meth. Phys. Res. A, vol. 703, pp.183-189, 2013. S. David et al. ”Comparison of three Resistor Network Division Circuits for the readout of 4x4 Pixel SiPM Arrays,” Nucl. Instr. Meth. Phys. Res. A, vol. 702, pp. 121e125, 2013. V. Popov et al. ”A novel readout concept for multianode photomultiplier tubes with pad matrix anode layout,” Nucl. Instrum. Meth. A, vol 567, pp. 319, 2006. M. Streun, G. Brandenburg, H. Larue, E. Zimmermann, K. Ziemons and H. Halling, ”Pulse Recording by Free-Running Sampling,” IEEE Trans. Nucl. Sci. vol.48, pp. 524, 2001. M. Georgiou, S. David, E. Fysikopoulos and G. Loudos ”Development of a SIPM based gamma-ray imager using a Gd3Al2Ga3O12:Ce (GAGG:Ce) scintillator array,” IEEE Nucl. Sci. Symp.& Med. Imag conf. M21-48, Oct 27- Nov 2, Seoul, Korea, 2013. CANCER RADIATION THERAPY: QUO VADIS? Мersini Мakropoulou. Physics Department, School of Applied Mathematical and Physical Sciences, National Technical University of Athens, Greece
Fig. 2. Energy spectra of a central scintillator element of the GAGG:Ce array under 22 Na and 137Cs irradiation.
Discussion e Conclusion: The acquired raw image of the GAGG:Ce crystal array under 511keV excitation shows a clear visualization of all (6x6) discrete scintillator elements with a mean peak to valley ratio equal to 40. The mean energy resolution was measured equal to 10.5% and 9% respectively under 511keV and 662keV irradiation. Taking into account the results conducted in a previous study of our group [9] under low energy isotopes i.e. 57Co and 99mTc (for SPECT applications) using the same detector module materials, (mean energy resolution equal to 16.1±0.52% at 140keV and 18.1±0.64% at 122.1keV with high peak to valley ratio above to17) a SPECT/PET hybrid detector
In oncology, treating cancer with a beam of photons is a well established therapeutic technique, developed over 100 years, and today over 50% of cancer patients will undergo traditional X-ray radiotherapy. However, ionizing radiation therapy is not the only option, as the highenergy photons releasing their energy into cancerous tumor can lead to significant damage to healthy tissues surrounding the tumor. Therefore, in nowadays, advances in ionizing radiation therapy are competitive to non-ionizing ones. For example, photodynamic therapy (PDT) is another type of cancer treatment that uses laser light to destroy tumors. Apart of PDT, laser light can be used to remove cancer or precancerous tumors or to relieve symptoms of cancer, such as bleeding or obstruction. In PDT, a photosensitizer is injected into a patient and distributed all over the patient’s body. After a couple of days, the photosensitizer is accumulated selectively in cancer cells. Laser light is then used to activate the agent and destroy cancer cells, in the presence of cellular oxygen. PDT is a non-invasive or minimally invasive therapeutic procedure (through flexible endoscopes). The use of minimally invasive techniques in the management of patients represents a very interesting treatment option. Moreover, as the major breakthrough in cancer management is the individualized patient treatment, new biophotonic techniques, e.g. photo-activated drug carriers, help the improvement of treatment efficacy and/or normal tissue toxicity. Additionally, recent studies support that lasers could ameliorate cancer proton therapy. It is reported that laser-driven proton acceleration offers a significantly cheaper and relatively convenient approach to generate a beam of protons and experiments in this direction indicate that protons in laser proton therapy (LPT) kill cancer cells as effectively as those from accelerators. Although the biophysical
Abstracts / Physica Medica 30 (2014) e75ee121
studies for laser-driven ion acceleration are still in their infancy, very promising radiobiological processes are reported, since protons and photons have a parallel destructive effect on the DNA of the targeted tumor cells. In this work we will present the laser-based future objectives for cancer radiation therapy, aiming to address the relevant advances in the ionizing and non-ionizing radiation therapy, i.e. protons and heavy ions therapy, as well as photodynamic targeted and molecular therapies.
THE CONTRIBUTION OF DIFFUSION TENSOR IMAGING AND MAGNETIC RESONANCE SPECTROSCOPY FOR THE DIFFERENTIATION OF BREAST LESIONS AT 3T Ioannis Tsougos a, Patricia Svolos a, Evanthia Kousi e, Evangelos Athanassiou b, Kiriaki Theodorou a, Dimitrios Arvanitis d, Ioannis Fezoulidis c, Katerina Vassiou c,d. a Department of Medical Physics, Medical School, University of Thessaly, Biopolis, Larissa, Greece; b Department of Surgery, Medical School, University of Thessaly, Biopolis, Larissa, Greece; c Department of Diagnostic Radiology, Medical School, University of Thessaly, Biopolis, Larissa, Greece; d Department of Anatomy-HistologyEmbryology, University of Thessaly Medical School, Larissa, Greece; e CR-UK and EPSRC Cancer Imaging Centre, Royal Marsden Hospital, Sutton, Surrey, United Kingdom Background: Conventional breast magnetic resonance imaging (c-MRI) combined with dynamic contrast-enhanced MR mammography (DCEMRM), constitute a powerful diagnostic strategy for screening breast lesions. Nevertheless, the high sensitivity of c-MRI and DCE-MRM comes with low specificity that may lead to ambiguous diagnosis and unnecessary biopsies [1,2]. Molecular MR imaging, such as proton MR spectroscopy (1H-MRS) or diffusion-weighted imaging (DWI)/diffusion tensor imaging (DTI), has shown promise as a complementary tool to improve MR specificity and explore the underlying biological characteristic of tumors, going a step further from c-MRI. Purpose: The purpose of the current study was to investigate whether the combination of 1H-MRS and DTI metrics further contribute to the determination of breast lesion’s aggressiveness. Materials and methods: Fifty-one women with known breast abnormalities from conventional imaging were examined on a 3T MR scanner. DTI was performed during breast MRI, and fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured in the breast lesions and the contralateral normal breast. FA and ADC were compared between malignant lesions, benign lesions, and normal tissue. 1H-MRS was performed after gadolinium administration and choline peak was qualitatively evaluated. Results: In the present study 1H-MRS showed a sensitivity of 93.5%, specificity 80%, and accuracy 88.2%. Choline detection dependence on tumor size was observed. FA was significantly higher in breast carcinomas compared to benign lesions (0.24±0.05 and 0.21±0.04, respectively). Mean ADC value was lower for malignant tumors, however no significant difference was observed. The combination of Cho presence and FA achieved higher levels of accuracy (90.3%) and specificity (84%) in discriminating malignant from benign lesions over Cho presence or FA alone. This correlation between Cho and FA may be explained based on two factors: (a) Cho is associated with active cell proliferation and (b) tumor growth, results in higher cell density, which might cause water molecules to diffuse with a higher degree of directionality, in contrast to benign lesions. Conclusion: In conclusion, applying DTI and 1H-MRS together, adds incremental diagnostic value in the characterization of breast lesions and may sufficiently improve the low specificity of conventional breast MRI. References: 1. Orel SG et al. MR imaging of the breast for the detection, diagnosis, and staging of breast cancer. Radiology 2001; 220: 13e30. 2. Yen Y et al. Dynamic breast MRI with spiral trajectories: 3D versus 2D. J Magn Reson Imaging 2000; 11: 351-9.
e79
CHARACTERIZATION OF OCCUPATIONAL EMF EXPOSURE TO MRI SYSTEMS E. Karabetsos a, N. Skamnakis a, G. Gourzoulidis b, P. Sandylos c, Chryssa Paraskevopoulou c, T.G. Maris d, A. Xristodoulou e. a Greek Atomic Energy Commission, Non-Ionizing Radiation Office, Greece; b Physical Agents Determination Department, ΚYАЕ (COHS), Ministry of Labor, Greece; c Ygeia Hospital; d Assistant Professor of Medical Physics, Medical Department, University of Crete, Greece; e General Director of Health & Safety at Workplace, Ministry of Labor, Greece European legislation concerning the protection of workers from exposure to EMF was recently completed by directive 2013/35/ЕU (26.6.2013), the transposition of which to the national legislations should have been concluded by July 2016. This directive is a specific one of the framework directive 89/391/EEC and is part of the overall legislation for Health and Safety of Workers (HSW). MRI systems have played a key role, both to the postponement of the former 2004/40 EMF directive and to the formation of the latest ICNIRP guidelines adopted by the new directive. On the other hand, MRI systems are associated with the exposure of personnel to various frequencies and modulations, arousing peculiar safety issues. It is important to stress out that directive 2013/35/EU excludes, under a prescribed scheme, MRI systems from the application of the exposure limits values (ELVs). In the framework of this derogation, increased surveillance is applied, meaning that the basic issues of HSW are of key importance. In order for this increased surveillance to apply to workers and as part of the risk assessment procedure, the knowledge of the exact occupational exposure levels and scenarios is highly important. Normally the MRI operator does not enter the examination room during the MRI scan, but in some cases this is possible. Measurements of the magnetic and electromagnetic fields were performed during the MRI scans, next to the examination bed and at the operation console. Different MRI systems (1,5 and 3T) have been chosen for measurements in order to access occupational exposure compared to the limit values given by the directive and to the main principles of HSW. Low frequency exposures resulting from the function of the gradients of the MRI system (rectangular pulses at the kHz region), as well as high frequency exposures due to the application of the main RF frequency (pulses in sinx/x envelope at the MHz region), were measured. One of the most important aspects of this work, was associated with the post-processing of the measured EMF signals in order to be comparable to the action level (AL) values of the directive. Keywords: electromagnetic fields, MRI occupational exposure, risk assessment, Health and Safety of Workers.
IMPROVEMENT OF DOSE DISTRIBUTION WITH IRREGULAR SURFACE COMPENSATOR IN WHOLE BRAIN RADIOTHERAPY Hideki Fujita, Nao Kuwahata, Hiroyuki Hattori, Hiroshi Kinoshita, Haruyuki Fukuda. Department of Radiation Oncology, Osaka Saiseikai Nakatsu Hospital, Osaka, Japan The aim of this study was to evaluate the dosimetries of whole brain radiotherapy (WBRT) using irregular surface compensator (ISC) compare with conventional radiotherapy. The ISC involves modulation of the beam with the multileaf collimator (MLC), and increases the dose homogeneity to the target volume while decrease the absorbed dose in irradiated tissues outside the targeted tissue. Treatment plans were produced for 10 patients. All treatments were carried out with 10 MV photon energy from a Clinac iX with 120 MLC (Varian Medical Systems, Palo Alto, CA, USA). The prescription dose was 30 Gy in 10 fractions at the isocenter. With Eclipse treatment planning system (Varian Medical Systems), the anisotropic analytical algorithm was used for the dose calculation. The tissue heterogeneity correction was used in all the treatment plans. For ISC, the skin flash tool application was used to extend the optimal fluence. These two treatment plans were compared in terms of does in the planning target volume (PTV), the dose homogeneity index (DHI), the maximum doses, eye and lens doses and the monitor unit (MU) counts