Investigation of depth dose distribution from electron beam at shallow depth by means of Gafchromic EBT3 polymer films and ionization chamber

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Abstracts / Physica Medica 32 (2016) 284–339

COMPARATIVE BETWEEN IMRT AND 3D-CRT FOR UPPER GI MALIGNANCIES A. Seguro Fernandez a,*, A. Ureña Llinares b, L. Diaz Gómez c, M.A. Iborra Oquendo b a

Medical Physics Department, Hospital Rey Juan Carlos, Móstoles, Spain Medical Physics Department, Hospital Universitario Puerta del Mar, Cádiz, Spain c Radiotherapy Oncology Department, Hospital Universitario Puerta del Mar, Cádiz, Spain ⇑ Corresponding author. b

Introduction. Adjuvant therapy after surgery in patients diagnosed with tumors of the upper abdominal area is a standard of care. In the field of radiotherapy is a challenge for proximity to PTV of multiple organs at risk (OARs) including spinal cord, liver, kidneys, lungs or heart. Purpose. Our goal of this study is to demonstrate the benefit of intensity modulated radiotherapy (IMRT) over 3D conformal therapy (3D-CRT) on OAR protection and improvement in planning target volume (PTV) coverage. Materials and methods. 11 patients were selected with upper digestive tract neoplasms with adjuvant treatment indication. The 3D-CRT technique involved two lateral fields and one or two oblique, with different table angles to avoid most volume of kidneys. IMRT technique involved several multi-field coplanar inverse planning. The prescription dose was 45 Gy in 25 fractions. Dose–volume histograms, dose homogeneity and dose to OAR were evaluated. Results. Both techniques are adequate with good coverage in the V95 with no evident differences in PTV dose homogeneity. IMRT was superior to 3DCRT with improvements in reducing the volume of both kidneys in the low dose region (V15) and liver as well (V30), achieving a lower spinal cord maximum dose. This can be explained by more number of the beams used in the IMRT technique. However, there were no significant improvements in PTV coverage. Conclusion. IMRT is a recommended technique for better protection of organs at risk without improving PTV coverages for upper GI malignancies. No conflict of interest. http://dx.doi.org/10.1016/j.ejmp.2016.07.131

RADIATION DOSES RECEIVED BY PATIENTS IN DIGITAL MAMMOGRAPHY: A FIRST INVESTIGATION IN MOROCCO Soumaya Boujemaa a, Hilde Bosmans b, Farida Bentayeb a a

Faculty of Sciences, University Mohammed V, Rabat, Morocco Medical Imaging Research Center, Department of Radiology, University Hospitals Leuven Herestraat 49, B 3000 Leuven, Belgium b

Introduction and objective. Digital mammography is being introduced worldwide for breast cancer diagnosis and screening. While the technique is known to offer a good image quality–dose balance, its introduction in specific regions should be investigated. Present study focuses on the absorbed radiation dose, and more in particular on estimations of average glandular dose (AGD).The present work concerns a dosimetric study in digital mammography in Morocco. Materials and methods. A dosimetric study was conducted in a Moroccan university hospital with system full-field digital mammography, Siemens Mammomat Inspiration. The average glandular dose of about hundred patients was calculated taking into account the entrance dose (tube output), half value layer and thickness of the compressed breast. Dose values were calculated with PMMA phantoms. Results. The results showed that almost values were located below the achievable dose limit curve of the European Guidelines.

For average thickness of 55 mm, the AGD is about 1.24 mGy for the Clinical–Caudal (CC) view and 1.32 mGy for the Mediolateral– Oblique (MLO) view with the same SD = 0.3. The results show also that the mean patients AGD is about 30% lower than that given by the PMMA. Conclusion. The results show an increase in the average glandular dose as a function of breast thickness. Average and maximal doses are in line with values obtained in European studies. This study will now be performed in more Moroccan hospitals and the data obtained could be used to work at breast cancer screening in our country. http://dx.doi.org/10.1016/j.ejmp.2016.07.132

BETATRON WITH VARIABLE ENERGY FOR IORT Evgeniia Sukhikh a,b,*, Leonid Sukhikh b, Evgeniy Malikov b a Tomsk Regional Oncology Center, Lenin Ave., 115, Tomsk 634050, Russia b National Research Tomsk Polytechnic University, Lenin Ave., 30, Tomsk 634050, Russia ⇑ Corresponding author.

Introduction. Since 2014 years in Tomsk Polytechnic University a new generation of betatrons for intraoperative radiation therapy (IORT) has been developing which has typical diameter approx. 70 cm at 6 MeV energy. The main advantages of the betatrons are that they operate at large frequency (400 Hz) at rather low pulse current, they have low energy spread and the relatively low cost of a device (typically $200,000). Purpose. The purpose of the project is to develop and test the compact betatron with adjustable energy of the extracted electron beam. Materials and methods. The depth dose distribution was measured along axis using plane-parallel Marcus ionization chamber and Gafchromic EBT-3 polymer film. Dosimetry was carried out following TG-51 and TRS-398 international protocols. The polymer films were calibrated using 10 MeV electron beam of Electa Axcess accelerator and 6 MeV electron beam of previous generation IORT betatron with constant energy. All measurements were performed in tissue-equivalent phantom with zero air gap. Results. The investigation of 3D dose distributions generated by new type of IORT source based on betatron was carried out in the energy range 2–6 MeV with 500 keV steps. In addition the radiation background distribution near the betatron was measured and it would be used for design of biological protection. Conclusion. According to the measured data it was proved that the extracted electron beam has designed energy that could be changed. The dose distributions allow assume that the compact IORT source based on betatron could be developed in the nearest future. http://dx.doi.org/10.1016/j.ejmp.2016.07.133

INVESTIGATION OF DEPTH DOSE DISTRIBUTION FROM ELECTRON BEAM AT SHALLOW DEPTH BY MEANS OF GAFCHROMIC EBT3 POLYMER FILMS AND IONIZATION CHAMBER Leonid Sukhikh a,*, Evgeniia Sukhikh b,a, Valentina Babicheva a, Evgeniy Malikov a a National Research Tomsk Polytechnic University, Lenin Ave., 30, Tomsk 634050, Russia b State Regional Autonomic Healthcare Institution ‘‘Tomsk Regional Oncology Center”, Lenin Ave., 115, Tomsk 634050, Russia ⇑ Corresponding author.

Abstracts / Physica Medica 32 (2016) 284–339

Introduction. Radiochromic film Gafchromic EBT3 can be used in the geometry when it is parallel to the beam axis allowing obtain absorbed dose depth distribution in a phantom during ‘‘single shot” of an accelerator. This method is useful for characterization of the electron beams of intraoperative accelerators because for this modality one needs a precise knowledge of the dose depth distribution starting from the phantom surface. Purpose. The purpose of this work is to compare experimentally and in simulation depth dose curves obtained using Gafchromic EBT3 film and ionization chamber. Materials and methods. The experimental comparison of the depth dose curves was carried out using 6 and 9 MeV electron beams of Elekta Synergy accelerator and 6 MeV electron beam of intraoperative therapy betatron. The dose distributions were measured by ionization chambers and by Gafchromic EBT3 films in different phantoms. The Monte-Carlo simulation of the process was carried out using PCLab software developed at Tomsk Polytechnic University that allows simulation of the beam interaction with the matter. Results. Experimental results show that percentage depth dose measured by the film at the shallow depths is less than the one measured by ionization chamber. Simulation results show the same difference. The simulation also shows that depth dose distribution ‘‘measured” by the film is close to the one in the pure water. Conclusion. Results show that depth dose distribution from electron beam in water measured by radiochromic film is more precise at shallow depths than the one measured by ionization chamber. http://dx.doi.org/10.1016/j.ejmp.2016.07.134

DOES INTRAVOXEL INCOHERENT MOTION (IVIM) INTRODUCE A NEW BIOMARKER IN MRI? A. Karapanagos, E. Karavasilis *, P.E. Efstathopoulos, L.S. Poulou, A. Athanasakos, G. Velonakis, G. Argiropoulos, P. Toulas, A. Passalis, C. Lioulios, L.N. Kelekis Second Department of Radiology, University General Hospital ‘Attikon’, School of Medicine, National and Kapodistrian University of Athens, Athens, Greece ⇑ Corresponding author. Introduction. Intravoxel Incoherent Motion (IVIM) imaging is a method that provides quantitative assessment all of the microscopic translational motions that could contribute to the signal acquired with diffusion weighted imaging (DWI) in MRI. The fundamental idea was that the molecular motion of water is randomly oriented in the capillary network at ultralow b values of diffusion imaging, mimicking a random walk. Diffusion parameters derived from IVIM model – perfusion F, true-ADC (Dslow), pseudo-ADC (Dfast) – have roused the researcher’s interest. Purpose. The aim of this study is to quantify the IVIM model diffusion parameters in patients with brain lesions compared to the normal appearing symmetric regions of the brain. Materials and methods. Patients underwent DWI on a 3T MRI system using an 8-channel sense head coil. DWI was performed with axial single-shot spin echo planar imaging (EPI) sequence with 10b values (0, 10, 15, 50, 80, 100, 200, 400, 700, 1000 s/mm2). The IVIM model diffusion parameters of Dslow, Dfast and F were calculated using a biexponential curve fitting model based on Levenberg–Marquardt algorithm applied in an in-house platform in Matlab. The statistical analysis between contra lateral regions was based on Student’s t tests.

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Results. Perfusion fraction F measured in brain damage regions showed significantly increased values compared to normal appearing symmetric regions. Parameters Dslow and Dfast had no statistical significance. Conclusion. The F parameter may consist a new sensitive biomarker for providing additional information to conventional diffusion parameters and predicting preliminary brain damage. http://dx.doi.org/10.1016/j.ejmp.2016.07.135

USEFULNESS OF DIFFERENT DTI PARAMETERS IN IDENTIFYING NEURODEGENERATIVE PROCESS: EVIDENCE FROM AMYOTROPHIC LATERAL SCLEROSIS E. Karavasilis a,*, F. Christidi b, P. Toulas a, P.E. Efstathopoulos a, M. Rentzos b, V. Zouvelou b, S. Xirou b, I. Evdokimidis b, L.N. Kelekis a a

Second Department of Radiology, University General Hospital ‘Attikon’, School of Medicine, National and Kapodistrian University of Athens, Athens, Greece b First Department of Neurology, Aeginition Hospital, Medical School, National and Kapodistrian University, Athens, Greece ⇑ Corresponding author. Introduction. Diffusion Tensor Imaging (DTI) reveals in vivo abnormalities in white matter (WM) fiber structure and has improved our knowledge of disease pathophysiology in several central nervous system (CNS) pathologies with WM involvement, especially through the analysis of different DTI indices. Purpose. To investigate the sensitivity of DTI parameters using tract based spatial statistics (TBSS) in amyotrophic lateral sclerosis (ALS), as a CNS disease with predominant WM involvement. Material and methods. We included 58 participants (36 patients with ALS and 22 healthy controls). All of them were scanned on 3.0T MR system, with 30-directional DTI and 3D-T1-weighted anatomical sequences. Whole-brain WM analysis was conducted using FSL and TBSS to estimate fractional anisotropy (FA), axial diffusivity (Ad) and radial diffusivity (Rd). Voxelwise statistical analysis was performed via a permutation-based inference for nonparametric statistical thresholding (5000 permutations). Two sample t-tests were applied to evaluate local alterations in DTI parameters (p < 0.05 with family-wise error correction for multiple comparisons). Results. In ALS patients we observed significant decreased FA and increased Rd (p < 0.05) in several WM areas (right > left), including corticospinal tract (CST), body of the corpus callosum and superior longitudinal fasciculus. Rd changes were more diffuse and found along the CST axis (WM of precentral gyrus, corona radiata, internal capsule). No changes were detected for Ad (p > 0.05). Conclusion. Decomposing the commonly used DTI parameters (FA and Mean Diffusivity) into Ad and Rd may be useful in identifying widespread WM changes in ALS and proved as a potential sensitive index for CNS neurodegenerative process. Disclosure. F.C. acknowledges support from the IKY Fellowships of Excellence for Postgraduate Studies in Greece – Siemens Program. We also acknowledge the Philips Medical System for providing all necessary research keys for MR/DTI sequence acquisition. The funders and/or contributors had no role in study design, data collection and analysis or preparation of the abstract. Finally, we would like to thank the patients with ALS and their families, as well as healthy volunteers for their willingness to participate to the present study. http://dx.doi.org/10.1016/j.ejmp.2016.07.136