M. P. Morigi

BNCT: neutron dose evaluation using a Monte Carlo code

The purpose of this work is to analyze dose distribution inside tissues. To do this, we performed some MCNP simulations using the neutron flux obtained from the Kyoto University Reactor. We have tried to analyze the behavior of neutrons in different types of tissues in relation to their depth. We have found that the value of dose from neutron interaction with 10B depends not only on 10B concentration inside the tissues (a higher concentration produces a higher dose), but also on the tissue density. In fact, tissues with a density considerably different from that of water receive a lower dose. Another dose contribution is given by the presence of 14N inside tissues: this dose contribution is lower compared with the previous one; it is influenced both by the tissue density and the percentage of nitrogen inside the tissue. Finally, the delivered dose decreases very quickly after a depth of about 4 cm, which implies that boron neutron capture therapy is not an effective therapy for the deepest tumors. However, there are some factors that can be taken into account to reach the deepest zone.

Dosimetry of High Intensity Electron Beams Produced by Dedicated Accelerators in Intra-Operative Radiation Therapy (IORT)

The technique of High Dose Intra-Operative Radiation Therapy (HDR-IORT) consists in the delivery of irradiation immediately following the removal of a cancerous mass, where the same incision is used to direct the radiation to the tumour bed. Given its particular characteristics, IORT requires dose measurements that are different from those requested in external radiotherapy treatments. The main reason lies in the fact that in this case a single high dose must be delivered to a target volume whose extension and depths will be determined directly during the operation. Since the possibility of devising a treatment plan using a TPS (Treatment Planning System) is not available, it is necessary to know the physical and geometric characteristics of the beam. Defining the physical characteristics of the beam entails both measuring the delivered dose and defining (monitoring) procedures. In any case a much higher dose will be released than occurs with conventional external accelerators. The ionization chamber recommended by the standard protocols for radiotherapy cannot be used because of the ion recombination inside the gas. In this work we propose the use of a calorimetric phantom, the Dosiort, to measure the beam properties. We describe the main characteristics and some preliminary results of the Dosiort System, which is proposed within the framework of a research project of the INFN (Italian National Institute of Nuclear Physics). The set-up is a solid phantom of density approaching 1 g/cm3 with sensitive layers of scintillating fibres at fixed a position in a calorimetric configuration for the containment of electrons of energy 4-12 MeV. The prototype will be able to define the physical and geometrical characteristics of the electron beam (energy, isotropy, homogeneity, etc) and to measure the parameters needed to select the energy, the intensity and the Monitor Units (MU) for the exposition: Percentage Depth Dose; Beam profiles; Isodose curves; Values of dose for MU.

3D tomographic reconstruction on HPC cluster of the Kongo Rikishi (Japanese wooden statue of the XIII century)

Computed Tomography is a non-destructive technique for which the object volume is reconstructed from a large series of radiographs acquired at different angles. Information can be retrieved as 2D cross section images allowing the inspection and the classification of the object; moreover, by processing tomographic data, a 3D numerical model of the full-volume sample can be obtained for virtual reality applications or digital archives storage. Computed Tomography is well known, specially in the medical field. However, it is a complex technique as soon as one wants to use it in a different way than in medicine (that means different scale, different energy range, different material composition and so on). The Kongo Rikishi is a Japanese wooden statue (over 200 cm of height) of the XIII century. The restoration has been carried out by the Conservation and Restoration Center La Venaria Reale, Turin, Italy. An high resolution Computed Tomography has been realized by the X-Ray Imaging Group of the Physics Department of Bologna University, Italy. To investigate the whole statue volume, up to 36 shootings are needed and for each of them 720 radiographs are acquired. To obtain the final volume (120 GB) 20 days of calculation are needed with a standard PC. In this work we will show the Proof of Concept that we have done using the Microsoft HPC cluster in Redmond. The Microsoft HPC environment has proved to be dramatically powerful and easy to use letting us reach important results quickly. Simply running many copies of the same software on different chunks of data using 20 cores has lead to an impressive speedup: up to a speed factor of 28. The same code, running on a new generation cluster of 32 cores, completed the elaborations with a speed rate factor of 75. These extraordinary results permit to reconstruct the volume in 6 hours instead of 20 days, making possible the real-time investigation of cultural objects.

HIGH-ENERGY COMPUTER TOMOGRAPHY MEASUREMENTS IN A MUSEUM AND ANALYSIS OF THE RADIOPROTECTION PROBLEM

Abstract In recent years there has been a growing demand from museums for computed tomography (CT) diagnostic measurements to be performed on famous artworks (sculptures and paintings) inside the museum itself in order to assess whether are they in good condition or need a restoration procedure. The problem of radioprotection becomes critical when the energy used in CT is high, as typically occurs in the case of CT measurements on sculptures, where linacs are used to produce the high-energy X-rays necessary to penetrate marble or metal. In this study we used Monte Carlo simulations in order to evaluate dose distribution inside a museum where a high-energy CT system is used for diagnostic measurements on a sculpture.

3D dosimetry of high intensity therapeutic electron beams

The technique of High Dose Rate Intra-Operative Radiation Therapy (HDR-IORT) consists in the delivery of irradiation immediately following the removal of a cancerous mass, where the same incision is used to direct the radiation to the tumour bed. Given its particular characteristics, IORT requires dose measurements that are different from those requested in external radiotherapy treatments. The main reason lies in the fact that in this case a single high dose must be delivered to a target volume whose extension and depth will be determined directly during the operation. Because of this peculiar characteristics, until now there is not a dosimetric system able to detect the electron beam giving at once a realtime response and an extensive spatial measure of the absorbed dose. In this work we present the results obtained by using two orthogonal layers of a calorimetric phantom, the Dosiort, to measure the beam properties. We describe the main characteristics and some results of the Dosiort System, which is proposed within the framework of a research project of the INFN (Italian National Institute of Nuclear Physics). The final set-up is a solid phantom of density approaching 1 g/cm3 with sensitive layers of scintillating fibres at fixed positions in a calorimetric configuration for the containment of electrons of energy 4–12 MeV. The prototype will be able to define the physical and geometrical characteristics of the electron beam (energy, isotropy, homogeneity, etc) and to measure the parameters needed to select the energy, the intensity and the Monitor Units (MU) for the exposition: Percentage Depth Dose; Beam profiles; Isodose curves; Values of dose per MU. In this paper we report in particular the measurement of the read-out dynamic range and the first qualitative study of the results which can be extracted from the measurements taken with the XY double layer in a test beam.