Characterization of the ESR response of alanine dosimeters to low-energy (1-40 keV) X-rays

The aminoacid L-a-alanine has attracted considerable interest for use in radiation ESR dosimetry and has been formally accepted as a secondary standard for high-dose (kGy) and transfer dosimetry . The accuracy of the method is quite high, largely due to the low dependence of the alanine response on various irradiation parameters (photon energies above 100 keV, dose rate, temperature, etc.). Furthermore, this system presents alinear response to dose, fairly high sensitivity, tissue equivalence, absence of fading, small dimensions, ruggedn ess, and non-destructive readout. In this work, we examined the energy dependence of alanine ESR dosimeters in the low energy X-photon energy range between…

Investigation of relaxation times of irradiated Fricke gels by means of nuclear magnetic resonance relaxometry

Fricke gel dosimeters are ideal candidates to provide 3D maps of dose distributions and are particularly useful in the plann ing and verification phase of radiotherapy treatments. One of the most effective experimental techniques to reconstruct dose maps is magnetic resonance imaging (MRI). This measures th e nuclear relaxation times variations induced by irradiation. In this work, we analyzed Fricke gels with and without Xylenol Orange by means of a single side-NMR relaxometer (which is abl e to provide information on both relaxation relaxation times T1 and T2 and is mainly used in the field of diagnostics for Cultural Heritage [1-2] to perform porosimetry meaurements). Our goal was to per…

Study of optical absorbance and MR relaxation of irradiated Fricke Xylenol Orange Gel Dosimeters

Studies on the optical absorbance spectra of Fricke xylenol orange gel dosimeters were performed, in the wavelength range from 300 nm to 800 nm, in order to highlight some particular characteristics that can affect the achievable precision. The spectra are different mainly due to the different types of xylenol orange that was used and to a lower extent due to the different gelling agents (agarose or gelatine). The characteristic of variation of absorbance spectra versus dose, however, are similar in the various cases and can explain some peculiarities, as apparent effects of dose threshold. Changes of spectral shapes appear over the time after irradiation. Magnetic resonance measurements pe…

Gel dosimeters for radiotherapy applications

Analisi NMR su gel di tipo Fricke irradiati con fasci routinari per la radioterapia: stabilità e sensibilità in funzione degli additivi

In questo lavoro sono presentate le misure effettuate tramite rilassometria NMR su campioni costituiti da una matrice gelatinosa drogata con ioni ferrosi comunemente chiamati dosimetri gel di tipo Fricke (FXG). La dosimetria con gel Fricke si basa sulla ossidazione degli ioni ferrosi (Fe2+) in ioni ferrici (Fe3+) all’interno di una matrice gelatinosa a seguito di irraggiamento (Schreiner, 2004). Tale processo è fortemente dipendente dalla dose somministrata (Marrale, 2014a). I dosimetri di Fricke sono tessuto-equivalenti, rispondono ad ogni tipo di radiazione ionizzante ed, assumendo la forma del contenitore in cui avviene la gelificazione, possono essere utilizzati per studiare l’effetto d…

Novel dosimetric gels for three-dimensional dose mapping in radiotherapy

One of the most recent and promising developments for radiotherapy (RT) dosimetry was the introduction of 3D radiation- sensitive gels. The gels are tissue equivalent, so they also serve as a phantom, and their response is largely independent of rad iation quality and dose rate. Some gels are infused with ferrous sulfate and rely on the radiation-induced oxidation of ferrous ions to ferric ions (Fricke-gels) . These gels suffer from spontaneous-oxidation and diffusion of ferric ions after irradiation; the latter is significantly reduced by chelating agents such as xylenol orange (XO) (Fricke-XO gels) [2]. Other formulations consist of dispersed monomers, and rely on radiation-induced cross-…