A new scintillating fiber dosimeter using a single optical fiber and a CCD camera

Radiotherapy treatments become more and more accurate, using very small irradiation fields and complex dose depositions. So small dosimeters for real time and in vivo dosimetry, suitable for photons as well as for electrons beams are highly desired. In this context, a scintillating fiber dosimeter (SFD) has been developed by the Laboratoire de Physique Corpusculaire de Caen (LPC Caen), France, in collaboration with one of the French regional center for cancer treatment Centre Regional de lutte contre le cancer F. Baclesse (CRLCC F. Baclesse), Caen, France, and the ELDIM Company, Herouville, France. This plastic dosimeter is water equivalent, and it is suitable for photons as well as for electrons beams without correction. It is a real time dosimeter, with an excellent signal to noise ratio, and a spatial resolution of about a few millimeters. The aim of this study was to reduce the size of the scintillator in order to improve the spatial resolution of this dosimeter. So, a new light collection device has been developed to reduce the length of the scintillator from 1 cm to 1 mm without loss in the signal to noise ratio. The accuracy of this improved prototype has been tested by comparison with standard ionization chambers and the difference between the two devices never exceeded one percent for photon and for electron irradiation beams. A first set of commercial SFD is under completion at ELDIM and it will be soon clinically tested in several French centers for cancer treatment

Developpement du DosiMap : Instrument de dosimetrie pour le contrôle qualite en radiotherapie

This thesis deals with the development of a new dosimetry device for the control of radiotherapy beams. This device is composed of a plane plastic scintillator which is set within a polystyrene phantom. When the DosiMap is irradiated, light is produced. This light is composed of scintillation and Čerenkov radiation, and is accurately measured by a CCD camera. The analysis of the light distribution enables us to deduce the dose distribution in the scintillator plan.This device has many advantages such as tissue equivalence, a good spatial resolution, and a linear response with regard to energy. It also provides immediate measurements, and as a consequence, it is a very adapted tool for clinical use.After the introduction about the basic notions of radiotherapy, the different steps of the DosiMap development are exposed in this thesis. In a first time, plastic scintillators have been tested to determine the best one for this application. Then, the deconvolution of scintillation and Čerenkov radiation have been studied, because we only use scintillation to calculate the dose distribution. The camera being in the irradiation room, a lead shield has also been developed to protect the CCD detector from scattered radiations. Finally, the dose calibration and the dose response of DosiMap are exposed.All this work made feasible the measurement of dose distributions with a precision which turns out to be better than 2% for homogeneous photon beams. Excellent results were also obtained when modulated intensity beams are used.Cette thèse porte sur le développement du DosiMap, un nouvel instrument de dosimétrie pour le contrôle des faisceaux de radiothérapie. Ce dispositif est basé sur l'utilisation d'un scintillateur plastique plan placé au sein d'un fantôme de polystyrène. La distribution lumineuse produite par le DosiMap sous irradiation, composée de scintillation et de rayonnement Čerenkov, est mesurée par une caméra CCD, puis analysée afin d'en déduire la distribution de dose déposée dans le scintillateur.Ce dispositif possède un certain nombre d'avantages. Il est équivalent tissus, présente une bonne résolution spatiale et une réponse linéaire en énergie. Il permet également d'effectuer des mesures de dose immédiates, ce qui rend son utilisation adaptée à une utilisation clinique.Après une introduction des notions de base de la radiothérapie, les différentes étapes du développement de cet instrument sont exposées dans ce mémoire. Différents scintillateurs plastiques ont, dans un premier temps, été testés afin de déterminer le mieux adapté à cette application. Seule la scintillation étant proportionnelle à la dose, la déconvolution de la scintillation et du rayonnement Čerenkov a ensuite été réalisée. Enfin, la caméra se trouvant en salle d'irradiation, il a été nécessaire de mettre au point un blindage afin de la protéger. La calibration en dose du dispositif ainsi que sa réponse dosimétrique sont alors exposées.Ce travail a permis de mesurer des distributions de dose avec une incertitude inférieure à 2 % pour des faisceaux de photons homogènes. D'excellents résultats ont également été obtenus dans le cas de faisceaux modulés en intensité

2D plastic scintillation dosimetry for photons

International audienc

Development of a dynamic phantom and investigation of mobile target imaging and irradiation in preclinical small animal research

LDM TEPInternational audienc

The influence of the solvent in fast neutron/gamma discrimination

The biphenyl/POPOP couple is known for its scintillation properties, but we describe in this letter its use for the discrimination between fast neutrons and gamma rays. More particularly, the influence of the matrix involved in this process is of interest, and for the first time pulse shape discrimination has been observed in non-common solvents such as heptane or ethanol. The discrimination efficiency of our systems is described in terms of figure of merit, angle between neutron and gamma lobes and scintillation performances

The influence of the solvent in fast neutron/gamma discrimination

The biphenyl/POPOP couple is known for its scintillation properties, but we describe in this letter its use for the discrimination between fast neutrons and gamma rays. More particularly, the influence of the matrix involved in this process is of interest, and for the first time pulse shape discrimination has been observed in non-common solvents such as heptane or ethanol. The discrimination efficiency of our systems is described in terms of figure of merit, angle between neutron and gamma lobes and scintillation performances

Dosimétrie par fibre plastique scintillante pour l'irradiation du petit animal

International audienceLes micro-irradiateurs récemment apparus dans le domaine de la recherche préclinique délivrent des faisceaux de rayons X dont la taille millimétrique et l'énergie (<250keV) sont parfaitement adaptés à l'échelle du petit animal. Les dosimètres à fibre scintillante sont de bons candidats pour la dosimétrie de tels faisceaux car ils associent un faible volume de détection à une lecture directe et leur composition est proche de celle de l'eau. Cependant, aux énergies d'irradiation du petit animal, une saturation de la scintillation (« quenching ») apparait, introduisant une dépendance en énergie. Ce travail présente d'une part la caractérisation de notre dosimètre par fibre scintillante ainsi que l'étude de la dépendance en énergie de sa sensibilité. Nous présentons d'autre part les premiers résultats de mesure dans des champs millimétriques

Comparative study of plastic scintillators for dosimetric applications

Plastic scintillators are widely studied for radiotherapy dosimetry because of their very interesting properties and especially their water equivalence. Nevertheless, to ensure accurate dose measurements, the properties of the scintillators must be very well known and adapted to this application. We studied six plastic scintillators manufactured by two different companies (Bicron and Amcrys-H) in terms of emission spectrum, light yield, time response, and linearity of the scintillation response with regards to the incident radiation energy. This last data, which is not available for plastic scintillator, is one of the most important in radiotherapy applications because it guarantees the proportionality between the dose deposited in the scintillator and the scintillation intensity. The experimental emission spectra (measured under X-rays) were similar to the manufacturer ones (measured under UV), except for one scintillator which presented incomplete wavelength shifts. This information is important to match the scintillator emission with the photodetector spectral response and to cope with the limiting phenomena of scintillation dosimetry (in particular the Čerenkov radiation). Bicron scintillators showed better scintillation efficiencies (ranging from 64 to 79% of Anthracene) than Amcrys-H ones (ranging from 40 to 63% of Anthracene). On the contrary, the decay times of the scintillators, similar to the ones provided by the manufacturers, were slightly better for the Amcrys-H scintillators (from 4.62 to 9.53 ns ) than for the Bicron ones (from 4.74 to 12.95 ns). This study showed that the response of the scintillation response become linear when irradiated by electrons above 100 keV and photons above 200–250 keV . One of the Bicron scintillators presented a worse criterion of linearity, and one of the Amcrys-H scintillators presented a better criterion. These results clearly show that plastic scintillators are very convenient for radiotherapy w- - h

Characterization of a scintillating fibre detector for small animal imaging and irradiation dosimetry

International audienceObjective:Small animal image-guided irradiators have recently been developed to mimic the delivery techniques of clinical radiotherapy. A dosemeter adapted to millimetric beams of medium-energy X-rays is then required. This work presents the characterization of a dosemeter prototype for this particular application.Methods:A scintillating optical fibre dosemeter (called DosiRat) has been implemented to perform real-time dose measurements with the dedicated small animal X-RAD® 225Cx (Precision X-Ray, Inc., North Branford, CT) irradiator. Its sensitivity, stem effect, stability, linearity and measurement precision were determined in large field conditions for three different beam qualities, consistent with small animal irradiation and imaging parameters.Results:DosiRat demonstrates good sensitivity and stability; excellent air kerma and air kerma rate linearity; and a good repeatability for air kerma rates >1 mGy s−1. The stem effect was found to be negligible. DosiRat showed limited precision for low air kerma rate measurements (<1 mGy s−1), typically for imaging protocols. A positive energy dependence was found that can be accounted for by calibrating the dosemeter at the needed beam qualities.Conclusion:The dosimetric performances of DosiRat are very promising. Extensive studies of DosiRat energy dependence are still required. Further developments will allow to reduce the dosemeter size to ensure millimetric beams dosimetry and perform small animal in vivo dosimetry.Advances in knowledge:Among existing point dosemeters, very few are dedicated to both medium-energy X-rays and millimetric beams. Our work demonstrated that scintillating fibre dosemeters are suitable and promising tools for real-time dose measurements in the small animal field of interest