FLASH radiotherapy (RT) is an emerging technique characterized by single ultra-high dose-rate irradiation delivering therapeutic doses in less than 200 milliseconds. Preclinical studies have demonstrated that such irradiation profoundly alters the radiobiological response of tissues, achieving tumor control comparable to conventional RT while offering greater protection to healthy tissues. In conventional RT, ionization chambers are the most commonly used beam monitoring devices. However, they are unsuitable for systematic radiobiological studies of FLASH irradiation due to the recombination effects at ultra-high doserates. This creates an urgent need to explore novel beam monitoring paradigms capable of supporting the unique demands of FLASH RT. The INFN FRIDA project investigates several aspects posed by the FLASH effect and its revolutionary potential. Two of these aspects are the focus of this thesis: the exploration of innovative solutions based on solid-state technologies - specifically silicon, diamond, and silicon carbide (SiC) - for beam monitoring applications, and the modification of an ELEKTA LINAC SL18 linear accelerator at the Department of Physics, University of Turin (UNITO). This modification enables the LINAC to deliver electron beams at FLASH RT dose-rates, which were characterized in terms of beam output stability, pulse constancy, and beam flatness. Various geometries of silicon sensors (strips, pads, and large segmented PIN sensors) coupled with multichannel front-end electronics readout systems were characterized under conventional and UHDR electron beams at the ELEKTA LINAC in Turin and the ElectronFLASH machine in Pisa, as well as under conventional proton beams at the CNAO National Hadrontherapy Center. Their response as a function of dose-per-pulse and bias voltage was evaluated. Furthermore, a polycrystalline CVD diamond (pCVD) sample was studied and characterized under electron beams from the ELEKTA LINAC. Finally, SiC sensors, extensively tested on UHDR beams at Pisa, were also exposed to the electron beams from the LINAC to conduct comparative performance analyses of silicon and SiC detectors under identical experimental conditions. The SiC sensors utilized in this work were manufactured by SenSiC STLab, a partner in this Ph.D. project. These sensors can be configured with a “ freestanding membrane” by removing the substrate through selective electrochemical doping etching. These devices were also studied beyond their FLASH RT applications, where SiC emerges as an ideal candidate for detection in harsh environments, requiring sensors to withstand high particle irradiation and/or elevated operating temperatures. For instance, this thesis includes a study on the radiation tolerance of SiC sensors to multiple damaging processes - both at room temperature and high temperatures - using the ion microprobe chamber installed at the Ruder Boˇskovi´c Institute (Zagreb, Croatia), which allowed small areas within the same device to be exposed to different ion beams. Additionally, I report on their potential use for X-ray beam position monitoring (XBPM), as an alternative to conventional beam intensity monitor (BIM) technologies which face numerous challenges, including diffraction effects, low signal strengths, non-uniform transparencies, and lack of position information. This study explores the potential of very thin SiC free-standing membranes as in-line, minimally-interfering beam position monitors with high lateral resolution for hard X-ray beamlines
Solid-state detectors for beam monitoring in FLASH radiotherapy and for other harsh environment applications(2025 Jan 23).
Solid-state detectors for beam monitoring in FLASH radiotherapy and for other harsh environment applications
MEDINA, ELISABETTA
2025-01-23
Abstract
FLASH radiotherapy (RT) is an emerging technique characterized by single ultra-high dose-rate irradiation delivering therapeutic doses in less than 200 milliseconds. Preclinical studies have demonstrated that such irradiation profoundly alters the radiobiological response of tissues, achieving tumor control comparable to conventional RT while offering greater protection to healthy tissues. In conventional RT, ionization chambers are the most commonly used beam monitoring devices. However, they are unsuitable for systematic radiobiological studies of FLASH irradiation due to the recombination effects at ultra-high doserates. This creates an urgent need to explore novel beam monitoring paradigms capable of supporting the unique demands of FLASH RT. The INFN FRIDA project investigates several aspects posed by the FLASH effect and its revolutionary potential. Two of these aspects are the focus of this thesis: the exploration of innovative solutions based on solid-state technologies - specifically silicon, diamond, and silicon carbide (SiC) - for beam monitoring applications, and the modification of an ELEKTA LINAC SL18 linear accelerator at the Department of Physics, University of Turin (UNITO). This modification enables the LINAC to deliver electron beams at FLASH RT dose-rates, which were characterized in terms of beam output stability, pulse constancy, and beam flatness. Various geometries of silicon sensors (strips, pads, and large segmented PIN sensors) coupled with multichannel front-end electronics readout systems were characterized under conventional and UHDR electron beams at the ELEKTA LINAC in Turin and the ElectronFLASH machine in Pisa, as well as under conventional proton beams at the CNAO National Hadrontherapy Center. Their response as a function of dose-per-pulse and bias voltage was evaluated. Furthermore, a polycrystalline CVD diamond (pCVD) sample was studied and characterized under electron beams from the ELEKTA LINAC. Finally, SiC sensors, extensively tested on UHDR beams at Pisa, were also exposed to the electron beams from the LINAC to conduct comparative performance analyses of silicon and SiC detectors under identical experimental conditions. The SiC sensors utilized in this work were manufactured by SenSiC STLab, a partner in this Ph.D. project. These sensors can be configured with a “ freestanding membrane” by removing the substrate through selective electrochemical doping etching. These devices were also studied beyond their FLASH RT applications, where SiC emerges as an ideal candidate for detection in harsh environments, requiring sensors to withstand high particle irradiation and/or elevated operating temperatures. For instance, this thesis includes a study on the radiation tolerance of SiC sensors to multiple damaging processes - both at room temperature and high temperatures - using the ion microprobe chamber installed at the Ruder Boˇskovi´c Institute (Zagreb, Croatia), which allowed small areas within the same device to be exposed to different ion beams. Additionally, I report on their potential use for X-ray beam position monitoring (XBPM), as an alternative to conventional beam intensity monitor (BIM) technologies which face numerous challenges, including diffraction effects, low signal strengths, non-uniform transparencies, and lack of position information. This study explores the potential of very thin SiC free-standing membranes as in-line, minimally-interfering beam position monitors with high lateral resolution for hard X-ray beamlinesFile | Dimensione | Formato | |
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