Monte Carlo simulation studies for spatially fractionated radiation therapy techniques

The purpose of this work was to evaluate the possible gain in tissue sparing in hadrontherapy when a spatial fractionation of the dose is used. Monte Carlo simulations (GATE v.6) have been used as a method to assess the dose distributions in a cylindrical water phantom (16 cm height and 16 cm of diameter). The phantom was irradiated with carbon and oxygen minibeams of 0.7 mm of beam width, and with protons in a grid geometry configuration. Several centre-to-centre distances, covering a 2 x 2 cm2 area, have been taken into account. The ratio of the peak-to-valley doses (PVDR) and the penumbrae was used as evaluation parameter, since PVDR is considered to be a very relevant dosimetric parameter for tissue sparing. Extremely high PVDRs values and very narrow penumbrae were obtained in all depths. This means that this new way of dose delivery might allow the use of higher and potentially curative doses in clinical cases where tissue tolerances are a limit to achieve a curative treatment. The high PVDR obtained and the small penumbrae in comparison with existing radiosurgery techniques, suggest a potential gain in healthy tissue sparing in those new techniques

Notulae to the Italian alien vascular flora: 11

In this contribution, new data concerning the distribution of vascular flora alien to Italy are presented. It includes new records, confirmations, exclusions, and status changes for Italy or for Italian administrative regions. Nomenclatural and distribution updates published elsewhere are provided as Suppl. material 1

Gadolinium dose enhancement studies in microbeam radiation therapy

Microbeam radiation therapy (MRT) is an innovative technique to treat brain tumors. The synchrotron generated x-ray beam, used for the treatment, is collimated and delivered in an array of narrow micrometer-sized planar rectangular fields. Several preclinical experiments performed at the Brookhaven National Laboratory (BNL) and at the European Synchrotron Radiation Facility (ESRF) have shown the sparing effect of the healthy tissue and the ablation of tumors in several animal models. It has also been determined that MRT yields a higher therapeutic index than nonsegmented beams of the same energy. This therapeutic index could be greatly improved by loading the tumor with high atomic number (Z) contrast agents. In this work, the dose enhancement factors and the peak to valley dose ratios (PVDRs) are assessed for different gadolinium (Z=64) concentrations in the tumor and different microbeam energies by using Monte Carlo simulations (PENELOPE 2006 code). A significant decrease in the PVDR values in the tumor, and therefore a relevant increase in the dose deposition, is found in the presence of gadolinium. The optimum energy for the dose deposition in the tumor while keeping a high PVDR in the healthy tissues, which guaranties their sparing, has been investigated

A dedicated processor for Monte Carlo computations in radioteraphy

A dedicated processor for Monte Carlo computations in radiotherapy treatment planning on FPGA based hardware is being developed at INFN, Cagliari. When performing Monte Carlo simulations of the radiation dose delivered to the human body, the Compton interaction of a photon with an electron is simulated. A fast, pipelined, cost effective design for real time simulation of the Compton interaction had been implemented. The inputs to the system are the energy and the normalized direction vectors of the incoming photon. The energy and the direction vectors of the scattered photon and the scattered electron are calculated. The energy distribution by the scattered electron along its path in a voxel space is then calculated which can be used to construct maps of dose distribution in real time

Internal dosimetry of [99m^{99m}Tc]NTP15‐5 radiotracer for cartilage imaging in preclinical and clinical models using the GATE Monte Carlo platform

International audienceThis study aims to perform dosimetry for [99m Tc]NTP15-5 radiotracer used in imaging of articular cartilage in rabbits and humans. The radiotracer (covered by a world patent WO 01/00621 A1) has been proposed in the past years for the study of cartilage in osteoarthritis diseases. A sensitive imaging approach is essential to quantify osteoarthritis progression and monitor response to new therapies. [99m Tc]NTP15-5 binds to cartilage proteoglycans whose decreased content is associated to a loss of biomedical function of cartilage. We have implemented the whole dosimetry study concerning this new radiotracer for rabbits and humans using the GATE Monte Carlo platform

Proton Irradiations at Ultra-High Dose Rate vs. Conventional Dose Rate: Strong Impact on Hydrogen Peroxide Yield

International audienceDuring ultra-high dose rate (UHDR) external radiation therapy, healthy tissues appear to be spared while tumor control remains the same compared to conventional dose rate. However, the understanding of radiochemical and biological mechanisms involved are still to be discussed. This study shows how the hydrogen peroxide (H2O2) production, one of the reactive oxygen species (ROS), could be controlled by early heterogenous radiolysis processes in water during UHDR proton-beam irradiations. Pure water was irradiated in the plateau region (track-segment) with 68 MeV protons under conventional (0.2 Gy/s) and several UHDR conditions (40 Gy/s to 60 kGy/s) at the ARRONAX cyclotron. Production of H2O2 was then monitored using the Ghormley triiodide method. New values of GTS(H2O2) were added in conventional dose rate. A substantial decrease in H2O2 production was observed from 0.2 to 1.5 kGy/s with a more dramatic decrease below 100 Gy/s. At higher dose rate, up to 60 kGy/s, the H2O2 production stayed stable with a mean decrease of 38% ± 4%. This finding, associated to the decrease in the production of hydroxyl radical (•OH) already observed in other studies in similar conditions can be explained by the well-known spur theory in radiation chemistry. Thus, a two-step FLASH-RT mechanism can be envisioned: an early step at the microsecond scale mainly controlled by heterogenous radiolysis, and a second, slower, dominated by O2 depletion and biochemical processes. To validate this hypothesis, more measurements of radiolytic species will soon be performed, including radicals and associated lifetimes

UHDR proton beam vs conventional: hydrogen peroxide as FLASH effect sensor

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UHDR proton beam vs conventional: hydrogen peroxide as FLASH effect sensor

International audienc

UHDR proton beam vs conventional: hydrogen peroxide as FLASH effect sensor

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Hydrogen peroxide formation to investigate the radiolytic ROS production mechanism under proton FLASH conditions

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