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This work describes the development of a reusable 2D detector based on radiochromic reaction for radiotherapy dosimetric measurements. It consists of a radiochromic gel dosimeter in a cuboidal plastic container, scanning with a flatbed scanner, and data processing using a dedicated software package. This tool is assessed using the example of the application of the coincidence test of radiation and mechanical isocenters for a medical accelerator. The following were examined: scanning repeatability and image homogeneity, the impact of image processing on data processing in coincidence tests, and irradiation conditions—monitor units per radiation beam and irradiation field are selected. Optimal conditions for carrying out the test are chosen: (i) the multi-leaf collimator gap should preferably be 5 mm for 2D star shot irradiation, (ii) it is recommended to apply ≥2500–≤5000 MU per beam to obtain a strong signal enabling easy data processing, (iii) Mean filter can be applied to the images to improve calculations. An approach to dosimeter reuse with the goal of reducing costs is presented; the number of reuses is related to the MUs per beam, which, in this study, is about 5–57 for 30,000–2500 MU per beam (four fields). The proposed reusable system was successfully applied to the coincidence tests, confirming its suitability as a new potential quality assurance tool in radiotherapy. [ABSTRACT FROM AUTHOR]

This work describes the development of a reusable 2D detector based on radiochromic reaction for radiotherapy dosimetric measurements. It consists of a radiochromic gel dosimeter in a cuboidal plastic container, scanning with a flatbed scanner, and data processing using a dedicated software package. This tool is assessed using the example of the application of the coincidence test of radiation and mechanical isocenters for a medical accelerator. The following were examined: scanning repeatability and image homogeneity, the impact of image processing on data processing in coincidence tests, and irradiation conditions—monitor units per radiation beam and irradiation field are selected. Optimal conditions for carrying out the test are chosen: (i) the multi-leaf collimator gap should preferably be 5 mm for 2D star shot irradiation, (ii) it is recommended to apply ≥2500–≤5000 MU per beam to obtain a strong signal enabling easy data processing, (iii) Mean filter can be applied to the images to improve calculations. An approach to dosimeter reuse with the goal of reducing costs is presented; the number of reuses is related to the MUs per beam, which, in this study, is about 5–57 for 30,000–2500 MU per beam (four fields). The proposed reusable system was successfully applied to the coincidence tests, confirming its suitability as a new potential quality assurance tool in radiotherapy.

Preclinical studies have shown that radiotherapy treatments benefit from ultra-high dose rate (UHDR) irradiations. These trigger the FLASH-effect, resulting in a strong decrease in normal tissue toxicity with conserved tumor control probability, compared with conventional irradiations. However, the beam parameters to trigger the FLASH-effect and the radiobiological mechanisms behind it remain to be elucidated. A limiting factor in many studies is the lack of accurate real time dosimetry. In this work an innovative solution for 2D real time dosimetry in UHDR electron beams is presented and characterized. The in-house developed ImageDosis system consists of a scientific camera, with high temporal resolution, and a coating, containing 12% of Y 3 Al 5 O 12 :Ce 3 + as scintillating material. Reference dosimetry was performed by means of radiochromic film, and a (C 38 H 34 P 2)MnBr 4 point scintillator was used to validate the pulse discrimination properties of the ImageDosis system. Irradiations were performed in two centers (Antwerp and Orsay), with an ElectronFlash accelerator. The ImageDosis system was tested with varying number of pulses, pulse length, pulse repetition frequency (PRF) and energy. In addition, its temporal resolution and 2D properties were investigated. The ImageDosis system showed negligible dose, dose rate and energy dependence for doses up to 13 Gy and average dose rates up to 140 Gy/s, with a dose per pulse up to 2 Gy and a PRF up to 300 Hz. The system is capable of discriminating and measuring the dose of individual pulses and shows promising 2D characteristics that need further optimization. [Display omitted] • The YAG-based ImageDosis system is a promising tool for real time UHDR dosimetry. • The ImageDosis system has shown not to be dose rate dependent. • The ImageDosis system provides 2D characteristics that are relevant for FLASH-RT. • The ImageDosis system has shown not to be energy dependent. • The ImageDosis system is capable of measuring individual pulses. [ABSTRACT FROM AUTHOR]

The aim of this work is to verify the potential use of GAFchromic™ EBT3 and FILMQA™ pro software for patient specific quality assurance (QA) for stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT) treatment plans in clinical routine use. In particular, encephalic, pulmonary and lymph node treatments plans were selected for this study. The agreement between the calculated and measured dose distributions were evaluated in terms of ɣ index with 3%3mm, 2%2mm, 1.5%1.5mm and 3%1.5mm criteria. The obtained results were then compared to the routine pretreatment verification method which uses electronic portal imaging device (EPID) and EPIQA analysis software. EBT3-FilmQA method results show a mean ɣ index passing rate >95% with 2%1.5mm analysis criteria and an improvement of about 7% compared with EPID-EPIQA method results. [ABSTRACT FROM AUTHOR]

The objective of this work is to demonstrate the feasibility of 2D dosimetry using optically stimulated luminescent (OSL) films based on MgB4O7:Ce,Li and to identify current limitations of this material for this application. A small quantity of test films was produced and read using a laser-scanning OSL reader after irradiation. The OSL luminescence and dosimetric properties were also investigated. The results demonstrate the advantage of the fast luminescence lifetime associated with Ce3+ emission (∼31.5 ns) for 2D dosimetry based on laser-scanning readout, since it minimizes the need for pixel-bleeding correction. The signal could be bleached satisfactorily using a fluorescence lamp and a long-pass filter. A dose response curve could be obtained with pieces of films simulating steep dose gradients and the dose response obtained using the signal from the center of such piece films was linear up to 10 Gy. Short and long-term phosphorescence components were observed in the luminescence signal of MgB4O7:Ce,Li, but their contribution with respect to the fast OSL signal is relatively small and should decrease with increasing laser scan rates. In spite of the high OSL sensitivity and linear response, the main disadvantage of MgB4O7:Ce,Li at the moment is the lack of a better understanding of the processes responsible for the sensitivity changes and fading of the OSL signal. Although the bleaching applied here allowed to reduce the residual OSL signal to minimum levels (

The goal of the present investigation is to explore the optically stimulated luminescent (OSL) properties of CaB 6 O 10 :Ce,LiCl in order to verify its viability as detector of ionizing radiation. Here, we investigate basic dosimetric and luminescent properties of this material. To this end, we carried out radioluminescence (RL), thermoluminescence (TL) and OSL measurements. We investigated the dose-response to ionizing radiation, the luminescent emission spectra, stability of the TL signal, and lifetime of the associated luminescent centers. The crystalline phase was verified by X-ray diffraction. TL measurement shows that the material is highly sensitive to ionizing radiation with a dominant TL peak at ~290 °C. RL measurement features a broad-band spectrum in contrast with the spectrum recorded during TL readout, which is narrow and was attributed primary to the 5d-4 f transition from Ce 3+ . The time-resolved OSL is characterized by two fast components, namely, 70.1(6) ns and143(4) ns and thus, suitable for 2D laser scanning readout. Dose-response curve was linear over the tested range (2 mGy−300 Gy) without trend to saturation. The current drawback is the OSL signal fading of up to 80% within 24 h by computing the initial intensity and of up to 50% by computing the integrated signal over 100 s. In principle, this issue may be solved by a fast heating of up to 80 °C prior to readout. [ABSTRACT FROM AUTHOR]

This work describes the synthesis of a new photostimulable phosphors based on Pb-doped CaB 6 O 10 , and presents an investigation on its luminescence and dosimetric properties. The crystalline phase was confirmed by X-ray diffraction. We performed radioluminescence (RL), thermoluminescence (TL) and optically stimulated luminescence (OSL) measurements to determine the material׳s luminescence sensitivity as a function of Pb concentration, dose response to ionizing radiation, as well as the luminescence emission spectra, thermal stability of the luminescence signal, and lifetime of the associated luminescence centers. The results shows that the material is highly sensitive to ionizing radiation, comparable or surpassing commercially available luminescence materials such LiF:Mg,Ti and Al 2 O 3 :C, with a dominant TL peak at ~200 °C and an OSL signal that can be ~99% read within ~20 s under current experimental conditions. The RL, TL and OSL signals are dominated by an emission band at ~320 nm, probably associated with 3 P 1 → 1 S 0 transition of Pb 2+ . Although the optimum Pb concentration was 3 mol% (nominal concentration used for synthesis), high sensitivity was observed for Pb concentrations >0.1 mol%. The luminescence decays with a 0.55 μs and a 5.1 μs lifetime and the dose response was linear in the range investigated (~2 mGy–1 Gy). A signal fading of up to 50% within 8 days was observed, the majority of this fading taking place in the first 5 h (40%) following irradiation. This study shall motivate further fundamental investigations on this material, which may lead to an alternative OSL material for dosimetry. [ABSTRACT FROM AUTHOR]

Complex and prolonged neuro-interventional radiology procedures using the biplane angiography system increase the patient's risk of radiation-induced cataract. Physical collimation is the most effective way of reducing the radiation dose to the patient's eye lens, but in instances where collimation is not possible, an attenuator may be useful in protecting the eyes. In this study, an eye lens protector was designed and fabricated to reduce the radiation dose to the patients’ eye lens during neuro-interventional procedures. The eye protector was characterised before being tested on its effectiveness in a simulated aneurysm procedure on an anthropomorphic phantom. Effects on the automatic dose rate control (ADRC) and image quality are also evaluated. The eye protector reduced the radiation dose by up to 62.1% at the eye lens. The eye protector is faintly visible in the fluoroscopy images and increased the tube current by a maximum of 3.7%. It is completely invisible in the acquisition mode and does not interfere with the clinical procedure. The eye protector placed within the radiation field of view was able to reduce the radiation dose to the eye lens by direct radiation beam of the lateral x-ray tube with minimal effect on the ADRC system. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the two dimensional (2D) and three dimensional (3D) radiotherapy dosimetric properties of PRESAGE® dosimeter using an in-house optical computed tomography (OCT) imaging system known as 3DmicroHD-OCT. Dosimetric properties for verification of intensity-modulated radiation therapy (IMRT) treatment technique were studied including dose linearity, dose integration, dose rate dependence and the percentage depth dose analysis. Nine cylindrical PRESAGE® of 5 cm diameter × 5 cm height were irradiated at 6 MV photon beam with different field geometry for the dose range of 0.1–15 Gy. We also irradiated PRESAGE® in the cuvette for UV–Vis analysis for the same dose range to verify the optical density value measured by the 3DmicroHD-OCT imaging system. The irradiation was repeated with EBT film dosimetry for the 2D analysis validation. The study shows that the optical density change increases as dose deposition increases on PRESAGE®, with R2 value better than 0.988. The same response was also recorded when multiple beam was integrated for the dose range investigated. The dose linearity result is consistent with the results obtained from UV–Vis spectrometry. It was also found that the dose rate variation does not affect the optical density change over the dose range investigated. PDD analysis of the PRESAGE® dosimeter investigated shows a good agreement with the ion chamber measurement. In summary, the study shows accurate 3D and 2D measurements of PRESAGE® and EBT film dosimeter were obtained using the 3DmicroHD-OCT imaging system. It shows potential for intensity-modulated radiation therapy (IMRT) treatment verification. • The prototype 3DmicroHD-OCT system provides 3D optical imaging for PRESAGE® dosimeter. • Multidimensional (2D and 3D) dose analysis was validated against EBT film. • The 3D dose integrated is linear from 0.1 to 15 Gy and independent of dose rates. [ABSTRACT FROM AUTHOR]

Two dimensional radioluminescence (RL) films were investigated for application in proton and carbon therapy dosimetry. The films are made of Al 2 O 3 :C,Mg micro powder in two sizes (38 µm and 7 µm) mixed with a water-equivalent binder. The films were irradiated behind different thicknesses of solid slabs and behind wedge shaped plastic absorbers. Bragg curves presented quenching effect attributed to the non-linear response of the RL signal as a function of proton linear energy transfer (LET). Experimental data and Monte Carlo simulations were utilized to acquire a quenching correction method, adapted from Birks' formula, to restore the linear dose response for particle therapy beams. The method for quenching correction was applied, reaching an agreement at the Bragg peak of 3 % for films with 38 µm median grain size phosphor and 1.5 % for films with 7 µm median grain size phosphor for the proton beams; and 2 % for films with 38 µm median grain size phosphor and 3 % for films with 7 µm median grain size phosphor for the carbon charged particles. [Display omitted] • Radioluminescence Al2O3:C,Mg films and a scientific camera. • Real time two-dimensional RL characterization along proton and carbon Bragg curves. • Films were irradiated behind different thicknesses of solid slabs and behind wedge shaped plastic absorbers. • The films present quenching with high LET. • A quenching correction was applied, good agreement along the Bragg curve. [ABSTRACT FROM AUTHOR]

A laser-scanning 2D dosimetry system based on the Optically Stimulated Luminescence (OSL) signal from Al 2 O 3 films was built and demonstrated. The main challenge of using the OSL from Al 2 O 3 for 2D dosimetry by laser scanning is the long lifetime (∼35 ms) of the main luminescence centers in this material ( F -centers). In this work, we demonstrated the possibility of performing 2D dosimetry by laser scanning using a combination of the fast UV emission of F + -centers (lifetime <7 ns) and the slow F -center emission of Al 2 O 3 :C, and an algorithm to correct for the slow F -center luminescence lifetime. We also investigated the possibility of using Al 2 O 3 :C,Mg, to take advantage of its greater F + -center emission compared to Al 2 O 3 :C. Results from 6 MV photon beam irradiations from a clinical linear accelerator were compared to radiographic and radiochromic film profiles showing a good qualitative agreement. [ABSTRACT FROM AUTHOR]

Abstract: Dosimetry of the monoenergetic raster-scanned beam of 12C carbon ions at GSI Darmstadt was performed using the LiF:Mg,Cu,P (MCP-N) 2-D thermoluminescence (TL) system. Several of TL foils of sizes and one were exposed to carbon ion beams of energies ranging between 88 and 430MeV/amu at doses ranging between 5 and 25Gy. The measured TL efficiency of the TL foil detectors, relative to 60Co -rays, varies between 0.30 at 88MeV/amu and 0.47 at 430MeV/amu and is well described by the microdosimetric One Hit Detector Model. In the investigated dose range the 2-D TLD system shows a linear dose response. Despite their appreciable energy response the 2-D TL foils based on LiF:Mg,Cu,P can be a useful tool for quality assurance of raster-scanned carbon ion beams. [Copyright &y& Elsevier]

• Radioluminescence using Al2O3:C and Al2O3:C,Mg films and a scientific camera. • Real time two-dimensional dosimetry has potential for patient and treatment QA. • The system has good uniformity, dose-rate response, and high spatial resolution. The Investigations of this article focus on the response of Al 2 O 3 :C and Al 2 O 3 :C,Mg radioluminescence films for medical dosimetry in various MV photon beams. A dosimetry system was configured using a scientific camera, attached to the head of the linear accelerator (LINAC), facing the beam's isocenter, where the films were placed. By using the appropriate filter and lens it is possible to measure real time two-dimensional dose-rate distributions. The key findings are that Al 2 O 3 :C,Mg films present a clear advantage compared to Al 2 O 3 :C ones, with no interference from afterglow, better film uniformity, high spatial resolution and suitability for small field beam dosimetry, while giving overall good dose-rate response in Flattening Filter (FF) and Flattening Filter Free (FFF) modes. The results show that our system can be used for planar real time dose rate assessment in medical photon dosimetry with manageable correction factors. [ABSTRACT FROM AUTHOR]

In particle-therapy, 2D dosimetry systems require high spatial resolution and linear dose response as the patient treatment show steep gradients of dose in depth. In this work we report on the characterization of the radiophotoluminescence (RPL) response from Al₂O₃:C,Mg films exposed to proton (61.3 MeV, 91.5 MeV, 155.5 MeV and 230 MeV) and carbon clinical beams (110 MeV/u). The film response is evaluated in terms of properties particularly important for relative dose measurements, as dose response, film uniformity and minimum detectable dose. The films, based on coatings with average grain sizes of ≈7 μm, demonstrate a better response than those used in our previous studies, with grain sizes of ≈47 μm. Moreover, the Linear Energy Transfer (LET) changes when penetrating through material and it is known that solid-state detectors change luminescence efficiency η HT,γ as a function of LET. Therefore, we performed a detailed characterization of our new film to evaluate its response as function of dose and LET. The η HT,γ curve, as a function of particle LET, obtained from discrete dose points (slabs) η HT,γ is compared with the η HT,γ curves from Al₂O₃:C (OSL) and Al₂O₃:C,Mg (RPL) films from our previous study. The η HT,γ curves are consistent with Birks' law, where we observe expected quenching for increasing LET. Additionally, we present 2D RPL images, using a wedge phantom, from Al₂O₃:C,Mg films irradiated with proton and carbon beams, which resulted in a 2D depth dose distribution of the Bragg curve and a comparable LET dependence with the data obtained with the slabs. The results confirm that the images obtained can be advantageously applied to obtain dose distribution in proton and carbon therapy without many corrections. • Improved Al 2 O 3 :C,Mg films irradiated with charged particle beams. • New luminescence efficiencies curves. • Full 2D image along the Bragg curve acquired with wedge phantom. [ABSTRACT FROM AUTHOR]

The objective of this work is to demonstrate the potential application of Al 2 O 3 :C and Al 2 O 3 :C,Mg optically stimulated luminescence (OSL) films for 2D dosimetry in magnetic resonance guided radiotherapy (MRgRT), a modality which combines two dosimetric challenges: small field dosimetry and dosimetry in the presence of a magnetic field. To achieve that, prototype Al 2 O 3 :C and Al 2 O 3 :C,Mg OSL films produced by Landauer (Glenwood, IL, USA) were characterized using a MRIdian system (ViewRay Inc., Mountain View, California, USA). The system was initially equipped with three 60Co heads on a ring gantry combined with a 0.35 T split-magnet MRI system and later upgraded with a 6 MV Flattening Filter-Free (FFF) linear accelerator, with a fixed dose rate of 600 MU/min. The dosimetric properties of the film material (Al 2 O 3 :C) in the magnetic field were first tested by irradiating samples of 7 mm in diameter read using a Risø TL/OSL automated reader for high precision. OSL films (Al 2 O 3 :C and Al 2 O 3 :C,Mg) were then tested at different doses and for two different intensity modulated radiation therapy (IMRT) treatment plans, for which the gamma analysis was performed using the 2D dose information obtained by readout of the films using a laser-scanning OSL reader. The results using the "point-dosimeter" samples showed deviations <4% with the delivered dose and variations within the same package of <4% (standard deviation of the data). The gamma analysis for IMRT plans showed pass rates >95% with a 3% - 3 mm criteria (>84% with a 2% - 2 mm criteria), with the failure typically happening in the edges of the film, not in the central high dose region. The results did not show any clear influence of the magnetic field and demonstrate the feasibility of Al 2 O 3 :C and Al 2 O 3 :C,Mg OSL dosimeters for 2D dosimetry in MRgRT. [ABSTRACT FROM AUTHOR]

As part of clinical safety for radiation therapy, quality assurance is vital to ensure that the delivered dose matches the prescribed dose for any targeted volumes and surrounding healthy tissue. A challenge when measuring the beam quality, especially for smaller sized beams, is having a water equivalent dosimeter with a high spatial resolution and the ability to perform accurate 2D mapping. In this work we use a plastic scintillator fibre optic dosimeter to measure a 2D beam profile of a 6 MV CLINAC photon beam with field sizes 30 × 30 mm2 and 10 × 10 mm2. The results supplement commissioning dosimetry data measured with three commercial dosimeters – two ionisation chambers (Scanditronix/Wellhofer CC13 and CC01) and a diode detector (IBA PFD-3G diode). We find that the 2D scanning system can cover the entire larger field in 27 min using 2 mm steps, providing a quick and thorough mapping of the beam for quality assurance. This system allows the step size to be varied as desired, something arrayed detectors cannot do. We measure an average uncertainty of 1% inside the field and 5% outside the field, demonstrating this system as a viable method for thorough mapping of 2D fields and as a tool for complimenting ionisation chamber measurements in thorough clinical quality assurance. • Scintillator fibre-optic dosimeters are shown to have a high spatial-resolution. • Two two-dimensional scans of a linear accelerator beam is presented. • The dosimeter is shown to have similar responses to commercial devices. [ABSTRACT FROM AUTHOR]