Marco Povoli

Medical physics aspects of the synchrotron radiation therapies: Microbeam radiation therapy (MRT) and synchrotron stereotactic radiotherapy (SSRT)

Stereotactic Synchrotron Radiotherapy (SSRT) and Microbeam Radiation Therapy (MRT) are both novel approaches to treat brain tumor and potentially other tumors using synchrotron radiation. Although the techniques differ by their principles, SSRT and MRT share certain common aspects with the possibility of combining their advantages in the future. For MRT, the technique uses highly collimated, quasi-parallel arrays of X-ray microbeams between 50 and 600 keV. Important features of highly brilliant Synchrotron sources are a very small beam divergence and an extremely high dose rate. The minimal beam divergence allows the insertion of so called Multi Slit Collimators (MSC) to produce spatially fractionated beams of typically ∼25-75 micron-wide microplanar beams separated by wider (100-400 microns center-to-center(ctc)) spaces with a very sharp penumbra. Peak entrance doses of several hundreds of Gy are extremely well tolerated by normal tissues and at the same time provide a higher therapeutic index for various tumor models in rodents. The hypothesis of a selective radio-vulnerability of the tumor vasculature versus normal blood vessels by MRT was recently more solidified. SSRT (Synchrotron Stereotactic Radiotherapy) is based on a local drug uptake of high-Z elements in tumors followed by stereotactic irradiation with 80 keV photons to enhance the dose deposition only within the tumor. With SSRT already in its clinical trial stage at the ESRF, most medical physics problems are already solved and the implemented solutions are briefly described, while the medical physics aspects in MRT will be discussed in more detail in this paper.

Optimization of double-side 3D detector technology for first productions at FBK

We report on the optimization of the technology aimed at the production of Double-Sided, Double-Column 3D detectors with full passing columns (3D-DTTC) at FBK (Trento, Italy). This R&D project is aimed at establishing a suitable technology for the production of 3D pixel sensors to be installed into the ATLAS IBL. We describe the main process modifications adopted on more recent 3D batches, to overcome the limitations affecting the first 3D batch, as arisen from its electrical characterization.

Layout and process improvements to double-sided silicon 3D detectors fabricated at FBK

In the past few years, very important progress has been made in the development of silicon 3D detectors, passing from the R&D phase with performance demonstration of a few prototypes to an industrialization phase, which led to the first production of 3D sensors to cover 25% of the ATLAS Insertable B-Layer (IBL) staves. Double-side 3D sensor technology developed at FBK (Trento, Italy) in collaboration with INFN proved successful to yield good quality detectors for the IBL. In spite of the good performance of the IBL sensors, it is possible to further improve the electrical characteristics of these devices while reducing the fabrication complexity and therefore the time required for a medium volume production. To this purpose, with the aid of TCAD simulations, we have investigated some modifications at both the layout and fabrication level aimed at improving the sensor breakdown voltage, both before and after irradiation, while reducing the number of lithographic steps required during fabrication. This paper reports on simulation results and preliminary experimental results from a new batch of 3D sensors implementing the proposed improvements.

Characterization of new FBK double-sided 3D sensors with improved breakdown voltage

We report on the characterization of a new version of double-sided 3D sensors fabricated at FBK (Trento, Italy). Owing to a modified design and improved technology, the new devices feature a sizable increase of the breakdown voltage with respect to the ones previously fabricated at FBK. Before irradiation, the breakdown voltage is in the range from ~70 V to ~ 130 V, after irradiation up to large fluences, it is typically larger than 200 V, that is high enough for proper 3D sensor biasing even after very high radiation fluences like those foreseen at the High Luminosity LHC.

Characterization of 3D-DDTC detectors on p-type substrates

We report on the electrical and functional characterization of 3D Double-side, Double-Type-Column (3D-DDTC) detectors fabricated on p-type substrates. Results relevant to detectors in the diode, strip and pixel configurations are presented, and demonstrate a clear improvement in the charge collection performance compared to the first prototypes of these detectors.

Hybrid detectors of neutrons based on 3D silicon sensors with PolySiloxane converter

We report on the first prototypes of hybrid detectors for neutrons from the INFN HYDE project. Devices consist of 3D silicon sensors coupled to PolySiloxane-based converters. The sensor design and fabrication technology are presented, along with initial results from the functional characterization of the devices in response to radioactive sources and neutron beams of different energies.

Multi-strip silicon sensors for beam array monitoring in micro-beam radiation therapy

We present here the latest results from tests performed at the ESRF ID17 and ID21 beamlines for the characterization of novel beam monitors for Microbeam Radiation Therapy (MRT), which is currently being implemented at ID17. MRT aims at treating solid tumors by exploiting an array of evenly spaced microbeams, having an energy spectrum distributed between 27 and 600keV and peaking at 100keV. Given the high instantaneous dose delivered (up to 20kGy/s), the position and the intensity of the microbeams has to be precisely and instantly monitored. For this purpose, we developed dedicated silicon microstrip beam monitors. We have successfully characterized them, both with a microbeam array at ID17, and a submicron scanning beam at ID21. We present here the latest results obtained in recent tests along with an outlook on future developments.

Thin silicon strip detectors for beam monitoring in Micro-beam Radiation Therapy

Microbeam Radiation Therapy (MRT) is an emerging cancer treatment that is currently being developed at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. This technique uses a highly collimated and fractionated X-ray beam array with extremely high dose rate and very small divergence, to benefit from the dose-volume effect, thus sparing healthy tissue. In case of any beam anomalies and system malfunctions, special safety measures must be installed, such as an emergency safety shutter that requires continuous monitoring of the beam intensity profile. Within the 3DMiMic project, a novel silicon strip detector that can tackle the special features of MRT, such as the extremely high spatial resolution and dose rate, has been developed to be part of the safety shutter system. The first prototypes have been successfully fabricated, and experiments aimed to demonstrate their suitability for this unique application have been performed. Design, fabrication and the experimental results as well as any identified inadequacies for future optimisation are reported and discussed in this paper.

Thin Silicon Microdosimeter Utilizing 3-D MEMS Fabrication Technology: Charge Collection Study and Its Application in Mixed Radiation Fields

New 10-<inline-formula> <tex-math notation=LaTeX>

3D silicon sensors with variable electrode depth for radiation hard high resolution particle tracking

mu text{m}