Many new X-Ray treatment machines using small and/or non-standard radiation fields, e.g., Tomotherapy, Cyber-knife, and linear accelerators equipped with high-resolution multi-leaf collimators and ...on-board imaging system, have been introduced in the radiotherapy clinical routine within the last few years. The introduction of these new treatment modalities has led to the development of high conformal radiotherapy treatment techniques like Intensity Modulated photon Radiation Therapy, Volumetric Modulated Arc Therapy, and stereotactic radiotherapy. When using these treatment techniques, patients are exposed to non-uniform radiation fields, high dose gradients, time and space variation of dose rates, and beam energy spectrum. This makes reaching the required degree of accuracy in clinical dosimetry even more demanding. Continuing to use standard field procedures and detectors in fields smaller than 3 × 3 cm
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, will generate a reduced accuracy of clinical dosimetry, running the risk to overshadowing the progress made so far in radiotherapy applications. These dosimetric issues represent a new challenge for medical physicists. To choose the most appropriate detector for small field dosimetry, different features must be considered. Short- and long-term stability, linear response to the absorbed dose and dose rate, no energy and angular dependence, are all needed but not sufficient. The two most sought-after attributes for small field dosimetry are water equivalence and small highly sensitive (high sensitivity) volumes. Both these requirements aim at minimizing perturbations of charged particle fluence approaching the Charged Particle Equilibrium condition as much as possible, while maintaining high spatial resolution by reducing the averaging effect for non-uniform radiation fields. A compromise between different features is necessary because no dosimeter currently fulfills all requirements, but diamond properties seem promising and could lead to a marked improvement. Diamonds have long been used as materials for dosimeters, but natural diamonds were only first used for medical applications in the 80 s. The availability of reproducible synthetic diamonds at a lower cost compared to natural ones made the diffusion of diamonds in dosimetry possible. This paper aims to review the use of synthetic poly and single-crystal diamond dosimeters in radiotherapy, focusing on their performance under MegaVoltage photon beams. Both commercial and prototype diamond dosimeters behaviour are described and analyzed. Moreover, this paper will report the main related results in literature, considering diamond development issues like growth modalities, electrical contacts, packaging, readout electronics, and how do they affect all the dosimetric parameters of interest such as signal linearity, energy dependence, dose-rate dependence, reproducibility, rise and decay times.
The FOOT (FragmentatiOn Of Target) experiment aims to measure the fragmentation cross-section of protons into H, C, O targets at beam energies of interest for hadrontherapy (50-250 MeV for H and ...50-400 MeV/u for C ions).
Given the short range of the fragments, an inverse kinematic approach requiring precise tracking capabilities in a magnetic volume has been chosen.
A key subsystem of this experiment will be the Microstrip Silicon Detector, based on 3 X-Y measuring station, each composed of two 150
μm
thick single side microstrip sensors. In this work, we present the results of characterization of the new version of a 64 channel low-noise/low power high dynamic range readout ASIC and subsequent tests of the first 150 um thick sensor prototype.
A series of tests were also performed to validate a novel “grazing angle” approach, where it is possible to change the track length below a given strip varying the incoming particle’s incident angle onto the sensor to test the electronics dynamic range without using high Z ions.
Radioguided surgery (RGS) is a medical practice which thanks to a radiopharmaceutical tracer and a probe allows the surgeon to identify tumor residuals up to a millimetric resolution in real-time. ...The employment of β− emitters, instead of γ or β+, reduces background from healthy tissues, administered activity to the patient, and medical exposure. In a previous work the possibility of using a CMOS Imager (Aptina MT9V011), initially designed for visible light imaging, to detect β− from 90Y or 90Sr sources has been established. Because of its possible application as counting probe in RGS, the performances of MT9V011 in clinical-like conditions were studied.11This work financed by Istituto Nazionale Fisica Nucleare, Italy, project CHIR2, and partially supported by Universitá degli Studi di Perugia, Italy , Fondo Ricerca di Base 2017, project SEISIPO.
Through horizontal scans on a collimated 90Sr source of different sizes (1, 3, 5, 7 mm), we have determined relationships between scan fit parameters and the source dimension, namely A quadratic correlation and a linear dependency of, respectively, signal integrated over scan interval, and maximum signal against source diameter, are determined. Horizontal scan measurements on a source, interposing collimators of different size, aim to determine relationships or correlations between scan fit parameters and source dimension. A quadratic correlation and a linear dependency of, respectively, signal integrated over scan interval, and maximum signal against source diameter are determined.
In order to get closer to clinical conditions, agar–agar phantoms containing 90Y with different dimensions and activities were prepared. A 90Y phantom is characterized by a central spot and a ring all around, for simulating both signal (tumor) and background (surrounding healthy tissue). The relationship found between scan maximum and 90Sr source diameter is then exploited to extract the concentration ratio between spot and external ring of the 90Y phantom. This observable, defined as the ratio between the tumor and the nearby healthy tissues uptake simulates the Tumor-to-Non-tumor Ratio (TNR). With the aim of evaluating the sensor’s ability to discriminate signal from background relying on the significance parameter, a further 90Y phantom, featuring a well-known and clinical-like activity will mimic the signal only condition. This result is used to extrapolate to different source sizes, after having estimated the background for various TNR. The obtained significance values suggest that the MT9V011 sensor is capable of distinguishing a signal from an estimated background, depending on the interplay among TNR, acquisition time and tumor diameter.
•A CMOS imager has been used as sensor for beta- emission from isotopes (90Y) of interest in Radioguided surgery.•Using a position scan a correlation between the source dimension and the shape of the response has been found.•The sensitivity of the sensor to tumor detection has been determined by studying the interplay among TNR, acquisition time and tumor diameter.
A new prototype 3D diamond dosimeter featuring laser-written graphitic surface connections and bonding pads has been tested. Diamond substrates are of interest to medical dosimetry as they are closer ...to bodily tissue equivalence than other solid-state materials. The device in this work was made with a polycrystalline chemical vapour deposition diamond substrate (pCVD) was laser processed to have internal 3D electrode columns and surface connections including the wire-bonding pads to make an all‑carbon detector, with no metal-diamond interfaces. Polycrystalline diamond can be produced with a larger area and cheaper cost than single crystal diamond, but has a relatively slow timing response due to charge trapping defects inside the substrate. To mitigate material defects, 3D sensor technology has been proposed. The 3D design has charge collection electrodes as columns spaced inside the material bulk perpendicular to the surface. When compared to the conventional ‘planar’ sensor design, the 3D arrangement decouples the charge collection distance from the thickness of the substrate, theoretically allowing for more efficient charge collection and the active volumes have smaller dimensions. The laser writing process used for the 3D columns was extended to make graphitic surface connections replacing conventionally used metal bonding contacts between the 3D graphitic columns and readout electronics. The removal of metal-diamond contacts in the detector volume reduces the distortion of the electric field close to the surface of the diamond. The prototype was tested using a laboratory X-ray tube and a clinical Elekta Synergy BM LINAC and was found to have dose-rate independence consistent with previous 3D diamond dosimeters but with lower operating voltages, the lowest being +6 V. Lower operating voltage is attributed to the removal of the electric field distortion at diamond-metal interfaces. This paper proposes the first implementation of an all‑carbon 3D diamond dosimeter using a polycrystalline substrate.
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•A 3D diamond detector has laser-inscribed electrode columns inside of the diamond.•3D design offers radiation tolerance in addition to diamond tissue equivalence.•Graphitic surface traces instead of metal are used to connect the electrodes.•Prototype device shows a current response linear with dose-rate.
In a carbon ion treatment the nuclear fragmentation of both target and beam projectiles impacts on the dose released on the tumor and on the surrounding healthy tissues. Carbon ion fragmentation ...occurring inside the patient body has to be studied in order to take into account this contribution. These data are also important for the development of the range monitoring techniques with charged particles. The production of charged fragments generated by carbon ion beams of 115-353 MeV/u kinetic energy impinging on carbon, oxygen, and hydrogen targets has been measured at the CNAO particle therapy center (Pavia, Italy). The use of thin targets of graphite (C), PMMA (C 2 O 5 H 8 ) and polyvinyl-toluene plastic scintillator (PS), <inline-formula> <tex-math notation="LaTeX">{\text{C}}_{b}{\text{H}}_{a} </tex-math></inline-formula> allowed to measure fragments production cross sections, exploiting a time-of-flight (ToF) technique. PS detectors have been used to perform the ToF measurements, while LYSO crystals have been used for the deposited energy measurement and to perform particle identification. Cross sections have been measured at 90° and 60° with respect to the beam direction. The measured proton, deuteron, and triton differential production cross sections on C, O, and H, obtained exploiting the target subtraction strategy, are presented here as a function of the fragment kinetic energy.
The characterization of high intensity charged particle beams at medical accelerators poses several challenges. In this work, we investigate the use of a highly segmented CMOS Image Sensors (CIS), an ...MT9T031 from Aptina, as a way to study the spatial homogeneity and the time stability of the beam. The approach relies on the possibility to define many adjacent small regions that perform the radiation flux measurement with sufficient precision (below 1%) to extract the spatial structure of the beam. The device has been exposed to a 10 MeV therapeutic electron beam at Santa Maria Hospital (Terni, Italy) to measure the electron flux at a distance of 140 cm. The whole sensor, using a non-linear calibration, has measured the value of the flux, then the segmentation approach has been applied to study the spatial structure of the beam. Concerning the variation in time, the current limitation of a rolling shutter CIS limits the capability to disentangle the time structure of the beam. However, in light of the possibility to obtain some CIS with the new global shutter architecture, having integration time of the order of a few tens of microseconds, the measurement procedure has been implemented and tested using ∼1Hz frequency frame-rate, to study its limits. Uncertainty of the order of 0.5% has been reached for measurement of both spatial and time beam homogeneity.
•CIS devices could be used as spatially very precise ionizing radiation detectors.•Non-linear calibration could be used to keep uncertainty at the 1% level.•The intrinsic homogeneous response of CIS to ionizing radiation over the whole surface open the way for uncertainty disentangling procedures.
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