X-Tream: a novel dosimetry system for Synchrotron Microbeam Radiation Therapy

Microbeam Radiation Therapy (MRT) is a radiation treatment technique under development for inoperable brain tumors. MRT is based on the use of a synchrotron generated X-ray beam with an extremely high dose rate ( ~ 20 kGy/sec), striated into an array of X-ray micro-blades. In order to advance to clinical trials, a real-time dosimeter with excellent spatial resolution must be developed for absolute dosimetry. The design of a real-time dosimeter for such a radiation scenario represents a significant challenge due to the high photon flux and vertically striated radiation field, leading to very steep lateral dose gradients. This article analyses the striated radiation field in the context of the requirements for temporal dosimetric measurements and presents the architecture of a new dosimetry system based on the use of silicon detectors and fast data acquisition electronic interface. The combined system demonstrates micrometer spatial resolution and microsecond real time readout with accurate sensitivity and linearity over five orders of magnitude of input signal. The system will therefore be suitable patient treatment plan verification and may also be expanded for in-vivo beam monitoring for patient safety during the treatment

In vivo

Rectal balloons are used in external beam prostate radiotherapy to provide reproducible anatomy and rectal dose reductions. This is an investigation into the combination of a MOSFET radiation detector with a rectal balloon for realtime in vivo rectal wall dosimetry. The MOSFET used in the study is a radiation detector that provides a water equivalent depth of measurement of 70 μm. Two MOSFETs were combined in a face-to-face orientation. The reproducibility, sensitivity and angular dependence were measured for the dual MOSFET in a 6 MV photon beam. The dual MOSFET was combined with a rectal balloon and irradiated with hypothetical prostate treatments in a phantom. The anterior rectal wall dose was measured in real time and compared with the planning system calculated dose. The dual MOSFET showed angular dependence within ±2.5% in the azimuth and +2.5%/−4% in the polar axes. When compared with an ion chamber measurement in a phantom, the dual MOSFET agreed within 2.5% for a range of radiation path lengths and incident angles. The dual MOSFET had reproducible sensitivity for fraction sizes of 2–10 Gy. For the hypothetical prostate treatments the measured anterior rectal wall dose was 2.6 and 3.2% lower than the calculated dose for 3DCRT and IMRT plans. This was expected due to limitations of the dose calculation method used at the balloon cavity interface. A dual MOSFET combined with a commercial rectal balloon was shown to provide reproducible measurements of the anterior rectal wall dose in real time. The measured anterior rectal wall dose agreed with the expected dose from the treatment plan for 3DCRT and IMRT plans. The dual MOSFET could be read out in real time during the irradiation, providing the capability for real-time dose monitoring of the rectal wall dose during treatment

Development and characteristics of silicon coordinate-sensitive detectors for high energy physics and nuclear physics

Developments of various silicon coordinate-sensitive detectors of particles and radiations for experiments in high energy physics and nuclear physics which are carried out by HERA-B, LHCb, ALICE collaborations and scientific establishments in Europe and Ukraine are presented. Detectors were designed with the help of custom software designed on the integrated circuits and manufactured at technological lines for commercial silicon IC that allow mass production. At realization of these works a number of technologies of silicon detectors production for various purpose and techniques of measurement of their electrophysical parameters were developed. Tests and studies of coordinate-sensitive detectors were carried out. It has been shown that they are providing reliable registration of useful events (a signal/noise ratio not less than 20 for non-irradiated samples) and high spatial resolution (for geometry of designs presented typical value - tens microns), also at the radiation load of few megarad and higher

Sensors of absorbed dose of ionizing radiation based on mosfet

The requirements to technology and design of p-channel and n-channel MOS transistors with a thick oxide layer designed for use in the capacity of integral dosimeters of absorbed dose of ionizing radiation are defined. The technology of radiation-sensitive MOS transistors with a thick oxide in the p-channel and n-channel version is created

ДОСЛIДЖЕННЯ ЕЛЕКТРОФIЗИЧНИХ ПАРАМЕТРIВ КРЕМНIЄВИХ P-I-N ФОТОДIОДIВ

Electrophysical parameters of test structures formed on high-resistivity silicon during manufacturing of p-i-n photodiodes have been investigated. Using specially constructed MIS test structures the following important electrophysical parameters of Si-SiO2 and Si-SiO2 -Si3 N4 systems characterizing the quality of silicon and semiconductor-insulator interface have been analyzed: surface generation velocity Sg, bulk generation life-time of minority carriers τg , fixed charge Qss and mobile charge Qi in dielectric. The influence of different types of insulators on Sg values and effect of voltage applied to the insulator on minority carrier generation velocity in MIS structures were found. The corellation between Qi and reverse currents in p-i-n photodiodes was revealed. High effectiveness of used test structures and proposed methodology for quality control of technological processes in p-i-n photodiodes processing have been establishedИсследованы электрофизические параметры тестовых структур на высокоомном кремнии, сформированных в процессе изготовления p-i-n фотодиодов. С помощью тестовых МДП структур специальной конструкции исследованы практически важные характеристики систем Si-SiO2 и Si-SiO2-Si3 N4, отражающие качество кремния и межфазной границыраздела диэлектрик-полупроводник: скорость поверхностной генерации Sg, объёмное генерационное время жизни неосновных носителей заряда в кремнии τg, а также значения фиксированного Qss и подвижного заряда в диэлектрике Qi. Установлено влияние типа диэлектрика на величину Sg, а также. напряжения на диэлектрике на скорость генерации не- основных носителей заряда в МДП структурах. Обнаружено взаимосвязь между величиной подвижного заряда с уровнем обратных токов диодов. Показана высокая информативность применяемых конструкций тестовых МДП структур и используемой методологии контроля качества технологии при разработке и изготовлении p-i-n фотодиодов.Досліджено електрофiзичнi параметри тестових структур на високоомному кремнiї, якi сформованi в процесi виготовлення p-i-n фотодiодiв. З допомогою тестових МДН структур спецiальної конструкцiї визначено практично важливi характеристики систем Si-SiO2 та SiSiO2-Si3N4, якi характеризують якiсть кремнiю та мiжфазової границi роздiлу дiелектрик — напiвпровiдник: швидкiсть поверхневої генерацiї Sg, об’ємний генерацiйний час життя неосновних носiїв заряду у кремнiї τg, а також значення фiксованого заряду Qss та рухомого заряду у дiєлектрику Qi . Встановлено вплив типу дiелектрика на величину Sg та напруги на дiелектрику на швидкiсть генерацiї неосновних носiїв заряду у МДН структурах. Виявлено взаємозв’язок величин рухомого заряду з рівнем зворотніх струмів діодів. Показано високу iнформативнiсть застосованих конструкцiй тестових МДН структур і використаної методології контролю якості технології при розробці та виготовленні p-i-nфотодiодiв

Studies of the characteristics of a silicon neutron sensor

Electrical characteristics and neutron dosimetry properties of silicon based p-i-n diodes are presented in support of the applications in the sensors for beam monitoring and medical physics. Both the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of silicon planar p-i-n diode sensors with cylindrical geometry have been theoretically modeled and experimentally measured. The shifts of the forward and reverse diode characteristics of the sensors versus the neutron dose have been obtained. It is shown that the neutron irradiation caused shift of the forward voltage of the p-i-n diodes is proportional to the current at which it is measured in the case of the low level injection or to the square root of the current in the case of the high level injection. The C-V characteristics and the full depletion voltages of the diodes have been estimated and experimentally verified. It is shown that the sensitivity of planar cylindrical structures as neutron sensors can be optimized by the selection of the device geometry and the current at which the measurement is performed

Usage of flexible carrier at assembling of silicon detectors

Perspective of aluminium-poliimide flexible carrier technology usage for assembling of different purpose detectors, including Si microstripe detectors is shown. Real constructs and assembly examples of different detector units with usage of flexible carrier technology, in particular microcables, adapters, cables, interconnections etc., are shown. Advantages of this technology are considered in comparison with ordinary wire connections in case of comparatively large amount of outlets and small step

A dual scintillator - dual silicon photodiode detector module for intraoperative gamma\beta probe and portable anti-compton spectrometer

A new approach has been investigated for the miniaturization and simplification of intraoperative gamma and beta probes that have recently found application in radioguided surgery and sentinel lymph node biopsy. The probe design that is based on dual annular scintillators coupled to specially designed silicon concentric dual photodiode (CDPD). This approach allows us to avoid fiber optics coupling and PMTs. Two channels readout front-end electronics including shaper amplifier attached directly to the back of the detector module has been proposed. Two geometries of Si dual photodiodes coupled to CsI(Tl) annular scintillators with light masking between them were fabricated and investigated. CDPDs have size 10 and 6 mm as well as 6 and 3 mm outer and inner diameters respectively. The spectroscopy properties of CDPD separately and coupled to CsI(Tl) dual scintillator were investigated on I-125, Co- 57 and Na-22 photon sources. Both detectors have demonstrated acceptable energy resolution (10% for 511-keV) for the proposed application with FDG isotopes. In the smaller detector the amplitude of the 511 keV photopeak from outer detector was less than in inner and is related to the light collection in the current geometry. When used in coincidence mode operation we observe a significant reduction in the measured Compton continuum level relative to the photopeak which is not significantly attenuated. The spatial resolution of detector module measured in the horizontal plane was 2-mm FWHM using a 0.5-mm collimated Tc-99m source

Urethral alarm probe for permanent prostate implants

We have developed a urethral dosimetry system for real time dose verification along the urethra during permanent implant prostate brachytherapy. The urethral alarm probe uses “spectroscopic dosimetry” to calculate the dose rate along the urethra in real time. The application of spectroscopic dosimetry for the urethral alarm probe was verified using Monte Carlo calculations. In phantom depth dose measurements as well as isotropy measurements were performed to verify the usefulness of the urethra alarm probe as an in vivo real time dosimeter