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This work deals with the dosimetric features of a particular phenolic compound (IRGANOX 1076®) for dosimetry of clinical photon and electron beams by using Electron Spin Resonance (ESR) spectroscopy. After the optimization of the ESR readout parameters (namely modulation amplitude and microwave power) to maximise the signal without excessive spectrum distortions, basic dosimetric properties of laboratory-made phenolic dosimeters in pellet form, such as reproducibility, dose-response, sensitivity, linearity and dose rate dependence were investigated. The dosimeters were tested by measuring the depth dose profile of a 6 MV photon beam. A satisfactory intra-batch reproducibility of the ESR signal of the manufactured dosimeters was obtained. The analysis of the ESR signal as function of absorbed dose highlights that the response of this material is linear in the dose range investigated (1-13 Gy) and is independent of the beam energy. The presence of an intrinsic background signal limits the minimum detectable dose to a value of approximately 0.7 Gy. Reliable and accurate assessment of the dose was achieved, independently of the dose rate. Such characteristics, together with the fact that IRGANOX 1076® is almost tissue-equivalent, and the stability of the ESR signal, make these dosimeters promising materials for ESR dosimetric applications in radiotherapy.

One of the most recent and promising developments in radiotherapy dosimetry was the introduction of 3D radiationsensitive gels. These gels present tissue equivalent composition and density, so they also serve as phantoms, and their response is largely independent of radiation 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-gel). In this work Fricke gel dosimeters produced with a matrix of poly-vinyl alcohol (PVA) cross-linked with glutaraldehyde (GTA) were analyzed with magnetic resonance imaging (MRI). This work focused on the analysis of the temporal diffusion of ferric ions through PVA-GTA gel dosimeters. PVA-GTA gel samples, partly exposed with 6 MV X-rays in order to create an initial steep gradient, were mapped using magnetic resonance imaging on a 7T MRI scanner for small animals. The results obtained with PVA-GTA gels were compared with those achieved with agarose gels, which is a standard dosimetric gel formulation. The analysis showed that the diffusion process is much slower (more than five times) for PVA-GTA gels than for agarose ones. Furthermore, MRI was performed on the PVA-GTA gels at 1.5 T with a clinical scanner in order to optimize the acquisition parameters and obtain high contrast between irradiated and non-irradiated samples. The PVA gels were found to offer good linearity in the range of 0-10 Gy and a stable signal for several hours after irradiation. The sensitivity was about 40% higher compared to gels produced with agarose as gelling agent. The effect of xylenol orange (XO) on the MRI signal was also investigated: gel dosimeters made without XO show higher sensitivity to x-rays than those made with XO. The dosimetric accuracy of the 3D gels was investigated by comparing their MRI response to percentage depth dose and transversal dose profile measurements made with an ionization chamber in a water phantom. The comparison of PVA-GTA gels with and without XO showed that the chelating agent reduces the MRI sensitivity of the gels. Depthdose and transversal dose profiles acquired by PVA-GTA gels without XO are more accurate and consistent with the ionization chamber data.

Since from the second half of the last century the spin trapping has found wide applications in chemistry, biology and medicine [1]. Of particular interest are the studied of the free radicals induced in biologically active molecules, such as DNA and proteins, when they are exposed to ionizing radiation. Their characterization allows to investigate the radiation-induced primary processes inside living cells. Indeed, ionizing radiations produce many kinds of free radicals through direct action; radicals can be formed also by indirect actions. However, the direct detection of these radicals is hard to obtain as they have a too short lifetime and this makes difficult to record them by conventional electron spin resonance (ESR) technique. This limitation can be overcome by means of spin-trapping method wherein these short-lived free radicals are converted using a diamagnetic scavenger (the spin trap) to longer-lived radicals (the spin adducts), which can be conveniently investigated by means of ESR. Here, we review a combined method of ESR and spin trapping to identify free radicals induced by direct ionization as well as OH-radical reactions in nucleic-acid related and protein-related compounds. ESR combined with spin trapping remains a useful method for clarifying these processes in a living organism.

We have studied the ESR response of alanine pellets with and without gadolinium exposed to the thermal column of the TRIGA Mark II research reactor at the University of Mainz (Germany). The choice of Gd as additive nucleus is due to its very high capture cross section to thermal neutrons and to the possibility for secondary particles produced after interaction with thermal neutrons of releasing their energy in the neighborhood of the reaction site. In particular, it was found that low concentration (5% by weight) of Gd brings about a neutron sensitivity enhancement of more than 10 times without heavily reducing tissue equivalence. Monte Carlo (MC) simulations of both response of alanine and Gd-alanine pellets with FLUKA code were performed and the results were compared with the experimental values.

The experimental activities here reported are focused on the analysis of the clinical applications of Fricke gel dosimeters produced with a matrix of Polyvinyl alcohol (PVA) cross-linked by adding glutaraldehyde (GTA). The analyses were performed by means of a 1.5 T clinical magnetic resonance imaging (MRI) scanner. The sensitivity of these dosimetric gels to clinical photon beams as well as the signal stability were suitably investigated. Furthermore, the effect of the xylenol orange on the MRI signal was analyzed. The results obtained show that these PVA-GTA gel dosimeters show good dosimetric features for possible future use for 3D dose mapping in clinical applications.

At the University of Pavia, a neutron irradiation facility has been constructed for preclinical in vitro and in vivo studies for BNCT. The facility is a wide channel (40 x 20 x 100 cm3) inside the graphite Thermal Column of the 250 KW research reactor TRIGA Mark II. The neutron field consists in a thermal component ranging from about 1010 and 109 cm-2s-1 along the longitudinal axis of the channel and it is uniform within 10% along the transversal axes. The fast neutron contamination (En > 1.58 keV) is more than 2 orders of magnitude lower. The gamma background coming from the core has been reduced with a 20 cm thick bismuth shield, however in the facility a gamma component is still present due to neutron capture reactions in Bi and C. A set of simulations with the Monte Carlo code MCNP has been conducted together with measurements using alanine dosimeters to determine the gamma background during irradiation. Attention has been put in the choice of the material surrounding the alanine dosimeters (r = 2.4 mm and height h = 30 mm) in order to ensure electronic equilibrium: hydrogenated materials have been discarded to avoid additional dose due to the (n, γ) reactions in H: graphite holders have been used to this end. Simulations have been performed to choose the calibration gamma source: the gamma spectrum present in the facility has been calculated as well as the spectra of energy deposition in alanine due to the charged secondary radiation (electrons). A photon source produced in a 6 MV electrons linear accelerator was found to be much more suitable than the 60Co source typically employed to calibrate dosimeters. To determine the thermal neutron contribution to the alanine response a lithium carbonate (Li-6 enrichment: 95%) shield (attenuation factor of about three orders of magnitude) was prepared to host the dosimeters during irradiation; measurements with and without shield were done; gamma dose rates were between 6.0 ± 0.3 Gy/h and 1.5 ± 0.1 Gy/h along the longitudinal axis of the Column. The comparison between the experimental results and the simulations allowed determining a sensitivity factor of alanine to thermal and fast neutron dose equal to 0.4.

The use of neutrons for cancer treatments has stimulated the research for beam characterization in order to optimize the therapy procedures in Neutron Capture Therapy (Altieri, 2008). Several research laboratories have shown an increasing interest aimed at extending the applicability of Electron Spin Resonance (ESR) dosimetry to radiotherapy with different types of radiation beams. In particular, ESR spectrometry provides absorbed dose measurements through the detection of the stable free radicals produced by ionizing radiations. The ESR dosimetric method has many advantages such as simple and rapid dose evaluation, the readout procedure is non-destructive, linear response of many organic and inorganic compounds (Baffa 2014). In this work we study the response of phenolic compounds with and without gadolinium addition for electron spin resonance (ESR) dosimetry exposed to a gamma and mixed (n, gamma) field mainly composed of thermal neutrons. The compound IRGANOX 1076 phenol gives a phenoxy radical stabilized by the presence of two bulky groups [3]. Moreover, its high molecular weight, the low volatility and the compatibility with the dosimeter binding material (paraffin) are advantages with respect to lower molecular weight phenols. In this work we report the ESR investigation of phenols pellets and thin films with and without Gd2O3 (5% by weight) exposed in the thermal column of the Triga Mark II reactor of LENA of Pavia. Thanks to their size, the phenolic films here presented are good devices for the dosimetry of beams with high dose gradient and which require accurate knowledge of the precise dose delivered. The choice of Gd as the additive nucleus has been made because we are interested in applications for mixed field (neutrons/photons) Gd-ESR dosimetry has an high neutron capture cross section and, furthermore, the high LET secondary particles release their energy entirely in the dosimeter. The low content of gadolinium guarantees a good tradeoff between the sensitivity to thermal neutrons. However, the use of gadolinium reduces or abolishes tissue equivalence because of its high atomic number (Marrale, 2015). The dosimetric features of these ESR dosimeters have been investigated. In particular, we analyzed the ESR spectra of these compounds and their dependence on microwave power and modulation amplitude, their response after gamma and neutron irradiations, the detection limits for both beam typologies, signal stability after irradiation. The results of ESR experiments are compared with Monte Carlo simulations aimed at obtaining information about the total dose measured by means of ESR dosimeters.

Alongside with the development of Neutron Capture Therapy (NCT) and the use of thermal neutrons for radiotherapeutic purposes, many efforts have been devoted to the characterization of the beam in order to optimize therapy procedures. Reliable dose measurements should be able to determine the various (neutrons and photonic) components of the mixed beam usually employed for therapy. This paper studies the effect of additives such as boric and gadolinium nuclei on the sensitivity of neutron organic (alanine and ammonium tartrate) dosimeters analyzed through Electron Spin Resonance (ESR) technique (Marrale, 2014). These dosimeters were exposed to a mixed (neutron-gamma) field mainly composed of thermal neutrons. The choice of 10B and 64Gd as nuclei additives is due to their very high capture cross section for thermal neutrons. Also, after the nuclear reaction with thermal neutrons are emitted particles, which in turn release their energy in the vicinity of the reaction site (Marrale, 2008). The irradiation with mixed field (neutron-gamma) were performed within the thermal column of the TRIGA reactor, University of Pavia. Dosimeters readout was performed through the Electron Spin Resonance spectrometer Bruker ECS106 located at the Laboratory of Dosimetry ESR / TL of the Department of Physics and Chemistry - University of Palermo. We found that the addition of Gadolinium allows to largely increase the sensitivity of the dosimeters for thermal neutrons. In particular, a low concentration (5% by weight) of gadolinium oxide leads to an improvement of the sensitivity of neutrons more than 10 times. In addition, for this low content of gadolinium the photon tissue equivalence is not heavily reduced. This experimental analyses are compared with computational analyses carried out by means of Monte Carlo simulations performed with the MCNP (Monte Carlo N-Particle) transport code. A good agreement was observed for alanine dosimeters.

Fricke Xylenol Gel (FXG) dosimetric system is based on the radiation induced oxidation of ferrous (Fe2+) to ferric (Fe3+) ions. The application of Fricke gels for ionizing radiation dosimetry is continuously increasing worldwide due to their many favorable properties. However, one of their shortcomings is that ferrous and ferric ions diffuse in the gel matrix. To maintain the spatial integrity of the dose distribution, Fricke gels must be undergoing measurement within a few hours of their irradiation, so that ferric ions remain close to their point of production. Thus, the spatial integrity of the dose distribution in the Fricke gel is maintained. The gel matrix also contributes to the oxidation of ferrous ions during irradiation, increasing the chemical yield of ferric ions in aqueous solution and increasing the sensitivity of the dosimeter. The oxidation of ferrous ions also causes a reduction of the longitudinal nuclear magnetic relaxation time T1 which can be measured by means of Nuclear Magnetic Resonance Relaxometry (NMR) and Magnetic Resonance Imaging (MRI). The results presented are related to an experimental investigation conducted on Fricke Gels characterized by gelatinous matrix of Agarose or PVA. The dose calibration curves are reported and discussed from the point of view of the dosimeter use in clinical radiotherapy. This work has highlighted that the optimization of additives inside gel matrix is fundamental for optimizing photon sensitivity of these detectors. We can conclude that FXG dosimeters with optimal ferrous ammonium sulfate content can be regarded as a valuable dosimetric tool to achieve fast information on spatial dose distribution.

La Radioterapia IntraOperatoria (IORT) È una modalità di trattamento in cui una singola dose di radiazioni è impartita direttamente al letto tumorale o al tumore durante l'intervento chirurgico, evitando di colpire i tessuti sani circostanti. Nel caso di irraggiamento alla mammella, una singola frazione di 21 Gy impartita al volume neoplastico durante la procedura chirurgica è equivalente ad una dose totale di 60 Gy che solitamente viene somministrata con la radioterapia frazionata. Questo lavoro riporta il confronto tra la risposta ESR di dosimetri di alanina e di camere a ionizzazione Markus per le misurazioni degli Output Factor (OF) di fasci di elettroni prodotti da un acceleratore lineare utilizzato per la IORT. Il confronto è stato completato dai calcoli Monte Carlo degli OFs determinati con il software di simulazione GEANT4 ed utilizzando l'applicazione dedicata alla IORT che consente di ottenere informazioni dettagliate sulla distribuzione di dose.

I dosimetri a gel di Fricke con xylenol-orange, analizzati otticamente, presentano alcune limitazioni se impiegati per misure di basse dosi (pochi Gy o meno), per irraggiamenti di lunga durata o per individuare procedure di calibrazione che permettano l'utilizzo in radioterapia. Le difficoltà derivano da variazioni nello spettro di assorbanza verosimilmente dovute a variazioni dei legami degli ioni ferrici con lo xylenol-orange. Sono state effettuate misure: i) di assorbanza ottica, anche spettrometrica, per dosimetri irraggiati a diverse dosi e a diversi tempi rispetto all'irraggiamento; ii) di rilassometria RM per valutare le variazioni dovute al solo aumento del numero di ioni ferrici.

We have used EPR to characterize a series of defects, which are characterized by tipical g-tensors, linewidths, intensity as function of the temperature. Mostly, signals arises from the presence of conduction electrons, and of so-called "edge states", that are unpaired electrons located at the edges of graphenic flakes; the relative molecular orbitals are not very muche extended as for low-lying orbitals, and are located within few atomic rows from edges with zig-zag topology. All the relative EPR signals are naturally and intrinsically generated by all graphitic materials. We now extend our study to the defects that are formed inside the graphenic structure. There is a full zoo of possible defects that can in principle originate EPR signals, like the presence of ad-atoms, holes, dislocation of atoms.We have started to study and analyze each type of defect from an experimental as well as from a theoretical point of view.

The Total Body Irradiation (TBI) is a radiation therapy technique widely used in clinical hemato-oncological treatment of patients that underwent bone marrow transplantation or peripheral stem cell transplantation. Typically, the administration of TBI treatment provides irradiations in 3 consecu-tive days with a double daily fractionation, although other dose fractionation modes have been widely adopted in the clinic procedures. Although this tech-nique allows to irradiate the whole body from head to toes, it has some limitations such as the lack of homogeneity of the dose distribution (which can show varia-tions of 20% in the different areas), irradiation of critical organs such as lungs, liver, intestine and eyeballs that receive a dose comparable to the nominal one and require appropriate shielding and a proper evaluation of the dose absorbed by them. The positive outcome of this type of radiation therapy is closely related to a precise and accurate measurement of dose distribution delivered to the patient in the various body districts. In this work the dose administered in a anthropo-morphic (RANDO) phantom during TBI treatments was evaluated by means EPR dosimetry with alanine. The estimate of the dose was carried out at various points inside the phantom that has been irradiated with a clinical TBI beam configuration by applying a proper shielding provided for the lungs. Doses measured through EPR were compared with those measured with a semiconductor diode

Among the various dosimetric techniques used for characterizing the radiation beams used in radiation therapy, the Electron Paramagnetic Resonance (EPR) arouses increasing interest for applications in various therapy procedures. When a compound is irradiated with ionizing radiations free radicals are produced and their concentration is proportional to the absorbed dose. This allows for dosi-metric measurements through EPR technique which is able to quantitatively de-termine the radical concentration. Our research group has started an investigation of the EPR response of some phenols compounds for possible dosimetric applications. In this work we report the EPR investigation of IRGANOX 1076 pellets and thin films exposed to various type of radiation beams. Phenols are compounds possessing a benzene ring attached to a OH group. After irradiation the final product is a stable phenoxy radical. The stability of such radi-cal can be improved by adding other alkyl chains which can be attached to the benzene ring. In particular, the phenol octadecyl3(3,5ditertbutyl4hydroxyphenyl) propionate (IRGANOX 1076) gave interesting results.

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-linking [3]. They develop into stable polymer structures, but they are often affected by significant toxicity. Recently, poly- vinyl alcohol (PVA) was identified as an alternative, promising matrix [4]. This work investigated new formulations based-on or loaded-with PVA, which are easy to manufacture and provide some of the most stable and sensitive gels available. In an extremely recent and original development, some of these gels can also be reset and reused.

In the last decades several research laboratories have shown an increasing interest aimed at extending the applicability of ESR-dosimetry to radiotherapy with different types of radiation beams. ESR is a spectroscopic method for investigating the structure and dynamics of such paramagnetic species. The concentration of radiation-induced free radicals is proportional to the energy released inside in the medium. Our research group has started an investigation of the ESR response of some phenols compounds for possible ESR dosimetric applications suitable features, such as high efficiency of radiation-matter energy transfer and radical stability at room temperature. In particular, the phenoloctadecyl−3−(3,5−di−tert.butyl−4−hydroxyphenyl)−propionatephenoloctadecyl−3−(3,5−di−tert.butyl−4−hydroxyphenyl)−propionate gave interesting results. In this work we report the ESR investigation of phenols exposed to clinical photon and electron beams.

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 delle radiazioni su fantocci antropomorfi da essi costituiti. Inoltre, la matrice di gel rallenta la diffusione degli ioni ferrosi (Fe2+) e ferrici (Fe3+) in modo che, se il gel viene analizzato entro un paio di ore dall’irraggiamento, gli ioni ferrici rimangono prossimi al loro punto di produzione. Inoltre, il gel favorisce l’ossidazione degli ioni ferrosi durante l'irraggiamento, in modo da aumentare la resa chimica degli ioni ferrici e quindi la sensibilità dei dosimetri. Lo scopo di questo lavoro è l'analisi tramite risonanza magnetica nucleare (NMR) delle proprietà di rilassamento protonico dei gel dosimetrici da noi preparati al variare della concentrazione dei centri paramagnetici (Fe3+) prodotti al variare della dose di irraggiamento. I gel Fricke sono stati irradiati con fasci di fotoni (LINAC) nel range clinico tra 0 e 20 Gy. Le analisi NMR sono state affiancate da acquisizioni di imaging a Risonanza Magnetica Nucleare (MRI) utilizzata in ambito ospedaliero (Galante, 2008). Per valutare la sensibilità a fotoni, abbiamo studiato la dipendenza dei tempi di rilassamento nucleari dalla dose, dalla concentrazione di solfato di ammonio ferroso contenuto all’interno dei gel e dalla presenza di indicatori ottici degli ioni metallici. Inoltre, è stata monitorata la stabilità del segnale per diversi giorni dopo l'irraggiamento. Le acquisizioni MRI sono state finalizzate alla mappatura 3D della dose su fantocci estesi. Vengono presentati e discussi i risultati ottenuti in relazione ad applicazioni dei dosimetri gel Fricke in ambito radioterapico. Questo lavoro evidenzia come valutazioni dosimetriche non possono prescindere dall’ottimizzazione della concentrazione degli additivi.

La RadioTerapia IntraOperatoria (IORT) è una modalità di trattamento in cui una singola dose di radiazioni è impartita direttamente al letto tumorale o al tumore durante l'intervento chirurgico, evitando di colpire i tessuti sani circostanti. La fabbricazione di acceleratori lineari mobili per elettroni dedicati alla IORT ha permesso una grande diffusione di questa tecnica radioterapica. Lo scopo di questo lavoro è il confronto tra la risposta di dosimetri di alanina letti tramite Risonanza Elettronica di Spin (ESR) e di camere a ionizzazione Markus per le misurazioni degli Output Factors (OFs) di fasci di elettroni prodotti da un acceleratore lineare utilizzato per la IORT. Gli OFs dei fasci di elettroni convenzionali ad alta energia sono normalmente misurati utilizzando camera di ionizzazione secondo protocolli dosimetrici internazionali. Tuttavia, i fasci elettronici utilizzati in IORT presentano caratteristiche quali (quali impulso di dose, spettro energetico e distribuzione angolare molto diversa dai fasci solitamente utilizzate in radioterapia esterna), per cui l'applicazione diretta di protocolli dosimetrici internazionali può introdurre ulteriori incertezze dosimetriche. Gli OFs ottenuti mediante dosimetri di alanina letti tramite ESR sono stati confrontati con quelli ottenuti con camere a ionizzazione di tipo Markus. Il confronto è stato completato da simulazioni Monte Carlo utilizzando l’applicazione dedicata alla IORT di Geant4 che consente di ottenere informazioni dettagliate sulla distribuzione di dose.

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 performed at various times after irradiation only reveal the slow changes due to the auto-oxidation effect, proving therefore that the modality of chelation of ferric ions by xylenol orange can affect the observed changes in the optical absorbance spectra.

Among the various dosimetric techniques used for characterizing the radiation beams used in radiation therapy, the electron spin resonance (ESR) arouses increasing interest for applications in various therapy procedures [1]. Free radicals are known to be produced when a compound is irradiated with ionizing radiations. The concentration of radiation-induced free radicals is proportional to the absorbed dos e and this allows for dosimetric measurements through ESR technique which able to quantitatively determine the radical concentration [2]. Our research group has started an investigation of the ESR response of some phenols compounds for possible ESR dosimetric ap plications suitable features, such as high efficiency of radiation-matter energy transfer and radical stability at room temperature [3-5]. In this work we report the ESR investigation of IRGANOX 1076 pellets a nd thin films exposed to various type of radiation beams (clinical photon and electron beams, neutron-photon mixed field).

In the last two decades the electron spin resonance (ESR) technique has been widely adopted for dosimetry of the radiation beams used in radiation therapy. In particular, alanine dosimtery is nowadays recognized as an international standard system for transfer dosimetry and for high doses. This is because among the various solid-state dosimeters the alanine ESR detectors present several advantages such as: tissue equivalence, linearity of its dose-response over a wide range, high stability of radiation induced free radicals, no destructive read-out procedure, no sample treatment before EPR signal measurement. In this presentation the main applications of ESR dosimetry for the characterization of various radiation beams used in clinical applications (such as photons, electrons, protons, charged ions and neutrons) will be reported. The possibility of improvement of ESR sensitivity to various radiation beams achieved through the use of additives will be discussed by considering the features of suitable dopants. Furthermore, since the ESR techniques is able to detect the interactions between free radicals produced by various types of radiations, recently this technique has been applied to provide information about the the linear energy transfer (LET) of the beams. These applications aimed at discriminating different radiation beams will be outlined.

Sono stati analizzati tramite rilassometria NMR ed acquisizioni MRI dosimetri gel di tipo Fricke realizzati utilizzando un'innovativa matrice gel sintetica e tessuto equivalente: Polyvinyl alcohol (PVA) attivando chimicamente il processo di gelificazione tramite l'aggiunta di Glutaraldehyde (GTA). Questi gel sono stati irradiati con fasci di fotoni (LINAC) nel range 0--20 Gy. Per valutare la sensibilità a fotoni è stata studiata la dipendenza dei tempi di rilassamento nucleari dalla dose e dalla concentrazione di ferro nei gel. Inoltre è stata monitorata la stabilità del segnale dopo l'irraggiamento. Acquisizioni preliminari MRI con uno scanner MRI da 7 T sono state affiancate alle misure NMR. Questo lavoro evidenzia come le valutazioni dosimetriche non possono prescindere dall'ottimizzazione della concentrazione degli additivi.

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 1 keV and 40 keV, which was not previously described. Furthermore, we analyzed the response enhancement of alanine loaded with gadolinium oxide. The ESR measurements were complemented by the information provided by a reference ionization chamber and a by semiconductor detection systems.

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 perform a more basic investigation on the MR relaxation features of these gels with and without xylenol orange in order to achieve a deeper understanding of the physical properties of these gels from the relaxation times.

Intracranial stereotactic radiosurgery (SRS) is a technique to deliver an ablative radiation dose with an extremely sharp dose gradient to small brain tumors. This tecnique allows to deliver high doses of radiation to the tumor sparing the surrounding healthy tissue. In this study the accuracy of the dose delivered in a SRS session by a non conventional radiotherapy machine, the TomoTherapy Hi-Art System, was investigated using an "end-to-end" test. This is perfome d by means of alanine Electron Paramagnetic Resonance (EPR) pe llets. The response of these dosimeters is compared to that of gafchromic films which are particularly suitable for two-dimensional dose verification providing accurate estimate of the distribution and of the gradients of the absorbed dose.

Introduction: Fricke Xylenol Gel (FXG) dosimetric system is based on the radiation induced oxidation of ferrous to ferric ions. In this kind of gels it can occur that ferrous and ferric ions diffuse in the gel matrix. To preserve the spatial distribution of the dose from diffusion, Fricke gels must be undergoing measurement within a few hours of their irradiation. Thus, the spatial integrity of the dose distribution in the Fricke gel is maintained. The oxidation of ferrous ions also causes a reduction of the longitudinal nuclear magnetic relaxation time which can be measured by means of nuclear magnetic resonance (NMR) instrumentation. In this work we performed NMR relaxometry and MR imaging investigations of Fricke Xylenol Gel characterized by gelatinous matrix of Agarose for possible applications in clinical photon beams used for radiation therapy. Materials and Methods: NMR relaxometry measurements were performed using an mq-ProFiler single-side relaxometer (Bruker Biospin). MRI imaging was realized on a 1.5 T Achieva scanner (Philips) with an eight channel head coil. The gels were irradiated in the clinical dose range (0– 20 Gy) with a Siemens Primus Low linear accelerator. Results: The main dosimetric features of the NMR signal were investigated. The linearity of the response with dose was observed. In order to assess the photon sensitivity we analyzed the dependence of NMR relaxation time on radiation dose with varying ferrous ammonium sulfate content inside FXG. The ferrous ammonium sulfate content which maximizes sensitivity is 1.75 mM. Furthermore, signal stability was followed for several days after irradiation. Aldo for MRI analysis the dose calibration curves were obtained also with MRI scanner. Moreover, a depth dose profile was reconstructed. Conclusions: We can conclude that FXG dosimeters with optimal ferrous ammonium sulfate content can be regarded as a valuable dosimetric tool to achieve fast information on spatial dose distribution.

Introduction: Among the various dosimetric techniques used for characterizing the radiation beams used in radiation therapy, the electron spin resonance (ESR) arouses increasing interest for applications in various therapy procedures. Free radicals are known to be produced when a compound is irradiated with ionizing radiations. The concentration of radiationinduced free radicals is proportional to the absorbed dose and this allows for dosimetric measurements through ESR technique which enables to quantitatively determine the radical concentration. In this work we report the ESR investigation of phenol pellets and thin films exposed to various types of radiation beams (clinical photon and electron beams, mix field neutrons/photons). Phenols are compounds possessing a benzene ring attached to a OH group. After irradiation the final product is a stable phenoxy radical. Materials and methods: Thanks to their size, the phenolic films here presented are good devices for the dosimetry of beams with high dose gradient and which require accurate knowledge of the precise dose delivered. Photon and electron irradiations at various energies were performed with the Siemens Primus Lowlinear accelerator present at ARNAS Ospedale Civico di Palermo, Italy. Thermal neutron irradiations were performed at the thermal neutron column at the Triga Mark II reactor of LENA (Laboratorio Energia Nucleare Applicata) of Pavia, Italy. ESR dosimeters were readout by means of a Bruker ECS106 spectrometer equipped with a TE102 rectangular cavity at room temperature. Results: The dose response of both pellets and films was found to be linear for all beams used in the dose range analyzed. The signal is very stable in the first days after irradiation. The possibility of obtaining depth dose profile was investigated. Conclusions: In conclusion, the phenols show radiometric features that designate it as a new material for EPR.

La sicurezza del paziente sottoposto a trattamenti terapeutici con radiazioni ionizzanti e il buon esito degli ultimi sono strettamente legati all’ottimizzazione delle procedure di esposizione alle radiazioni ionizzanti. In particolare è fondamentale arrecare il danno minore possibile ai tessuti sani che circondano la neoplasia da trattare. Rispetto ai campi di radiazione convenzionali utilizzati in radioterapia (fotoni), le particelle cariche pesanti (protoni e ioni carbonio) offrono diversi vantaggi quali la bassa dispersione laterale, l’alta efficacia biologica (RBE) nella regione del picco di Bragg ed un profilo di dose caratteristico in profondità del tutto differente da quello dei fotoni. Queste caratteristiche rendono particolarmente vantaggioso l’uso di queste particelle per il trattamento di tumori radio-resistenti localizzati vicino agli organi a rischio. Tra i rivelatori a stato solido usati in ambito dosimetrico, trovano largo utilizzo i dosimetri a Risonanza Elettronica di Spin (ESR) a base di alanina per le loro caratteristiche dosimetriche quali la tessuto-equivalenza per fotoni, la linearità di risposta alla dose in un ampio range, l’alta stabilità nel tempo del segnale radioindotto, la non distruttività della procedura di lettura, l’indipendenza dal dose-rate; inoltre non è richiesto alcun trattamento del campione prima della misura ESR e i dosimetri hanno un costo decisamente basso. Queste peculiarità, associate alla possibilità di riconoscere le varie componenti di un campo misto di radiazioni, rendono l'alanina un buon candidato per effettuare stime di dose durante l’uso di fasci di protoni e ioni carbonio. L'obiettivo principale del presente lavoro è quello di studiare la risposta di pellets di alanina analizzati tramite ESR irradiati con fasci di ioni carbonio utilizzati in ambito clinico. Nello specifico, per gli ioni carbonio sono stati condotti studi dosimetrici in acqua ed in presenza di disomogeneità del mezzo (come all'interfaccia osso-acqua) per simulare uno scenario quasi-clinico. Gli esperimenti sono stati condotti presso il Dipartimento di Biofisica del GSI Helmholtzzentrum in Germania utilizzando un fascio modulato attivamente usato per il trattamento di tumori in profondità. I risultati sperimentali sono stati modellizzati e confrontati con I dati del treatment plannig system (TPS).

Intra-operative radiation therapy (IORT) is a treatment modality where a single high dose of radiation is delivered directly to the tumor bed or to the exposed tumor during the surgical intervention, while avoiding surrounding dose-limiting structures. Mobile electron linear accelerators dedicated to IORT have been manufactured which have promoted a local large diffusion of this radiotherapy modality. For breast irradiation, a single fraction of 21 Gy delivered on the target volume during the surgical procedure is equivalent to the total dosage (60 Gy) usually delivered during 30 external fractionated radiotherapy at 2Gy/fraction. Alternatively, a single dose of 10 Gy can be administered as Intra-Operative Boost to the tumor bed, followed by hypo-fractionated or conventional external beam whole breast radiotherapy. This work reports a comparison between the response of alanine and Markus ionization chamber carried out for measurements of the output factors (OF) of electron beams produced by a linear accelerator used for IORT. Output factors (OF) for conventional high-energy electron beams are normally measured using ionization chamber according to international dosimetry protocols. However, the electron beams used in IORT have characteristics of dose per pulse, energy spectrum and angular distribution quite different from beams usually used in external radiotherapy, so the direct application of international dosimetry protocols may introduce additional uncertainties in dosimetric determinations. The high dose per pulse could lead to an inaccuracy in dose measurements with ionization chamber, due to overestimation of ks recombination factor. Furthermore, the electron fields obtained with IORT-dedicated applicators have a wider energy spectrum and a wider angular distribution than the conventional fields, due to the presence of electrons scattered by the applicator’s wall. For this reason, a dosimetric system should be characterized by a minimum dependence from the beam energy and from angle of incidence of electrons. This become particularly critical for small and bevelled applicators. All of these reasons lead to investigate the use of detectors different from the ionization chamber for measuring the OFs. Furthermore, the complete characterization of the radiation field is achieved also by the use of Monte Carlo Geant4 simulations which allows to obtain detailed information on dose distributions. We compared the output factors obtained by means of alanine dosimeters and Markus ionization chamber. The results are characterized by a good agreement of response of alanine pellets and Markus ionization chamber and Monte Carlo results (within about 3%) for both flat and bevelled applicators.

Fricke Xylenol Gel (FXG) dosimetric system is based on the radiation induced oxidation of ferrous (Fe2+) to ferric (Fe3+) ions. The application of Fricke gels for ionizing radiation dosimetry is continuously increasing worldwide due to their many favorable properties. However, one of their shortcomings is that ferrous and ferric ions diffuse in the gel matrix. To maintain the spatial integrity of the dose distribution, Fricke gels must be undergoing measurement within a few hours of their irradiation, so that ferric ions remain close to their point of production. Thus, the spatial integrity of the dose distribution in the Fricke gel is maintained. The gel matrix also contributes to the oxidation of ferrous ions during irradiation, increasing the chemical yield of ferric ions in aqueous solution and increasing the sensitivity of the dosimeter. The oxidation of ferrous ions also causes a reduction of the longitudinal nuclear magnetic relaxation time T1 which can be measured by means of Nuclear Magnetic Resonance Relaxometry (NMR) and Magnetic Resonance Imaging (MRI). The results presented are related to an experimental investigation conducted on Fricke Gels characterized by gelatinous matrix of Agarose or PVA. We performed NMR relaxometry investigations which allow for direct measurements of the relaxation times in samples exposed to clinical photon beams. The main dosimetric features of the NMR signal were investigated. The gels were irradiated in the clinical dose range between 0 and 20 Gy. In order to assess the photon sensitivitywe analyzed the dependence of NMR relaxation time on radiation dose with varying ferrous ammonium sulfate content inside FXGs. Furthermore, signal stability was followed for several days after irradiation. These measurements were preliminary to MRI analysis which can permit 3D dose mapping. In order to optimized the MRI response a systematic study was performed to optimize acquisition sequences and parameters. In particular, we analyzed for inversion recovery sequences the dependence of MRI signal on the repetition time TR and on the inversion time TI . The dose calibration curves are reported and discussed from the point of view of the dosimeter use in clinical radiotherapy. This work has highlighted that the optimization of additives inside gel matrix is fundamental for optimizing photon sensitivity of these POSTERS 355 detectors. We can conclude that FXG dosimeters with optimal ferrous ammonium sulfate content can be regarded as a valuable dosimetric tool to achieve fast information on spatial dose distribution.

The main gol of the present work is to investigate the response behaviour of alanine EPR pellets in clinical proton anc carbon ion beams. Proton irradiations were carried out at PSI (Switzerland) using both passive and active scattering modality, whereas, C ions irradiation were performed at GSI (Germany) adopting the raster scanning modality.

Laser-driven proton has recently gained a great interest as an alternative to conventional and more expensive acceleration techniques. These ion beams have desirable qualities such as small source size, high luminosity and small emittance to be used in different physics fields. This is very promising specially for the future perspective of a new concept of hadrontherapy based on laser-based devices could be developed, replacing traditional accelerating machines. ELIMED (Medical Applications at Extreme Light Infrastructure) is a task-force originally born by an idea of ELI-Beams (Prague) and INFN-LNS (Italian Institute for Nuclear Physics of Catania) researchers. ELIMED main goal is to perform proof-of-principle experiments aimed to demonstrate that laser-accelerated high-energy proton beams (up to 70 MeV in the first phase) can be potentially used for the specific case of ocular proton therapy. In this work we report the investigation of the dosimetric features of alanine pellets exposed to protons produced by means of the CATANA (Centro di AdroTerapia e Applicazioni Nucleari Avanzate) proton therapy facility. This analysis is preliminary for the application of the alanine dosimeters in laser-driven proton beams. ESR spectrometry with alanine is now widely recognized as the most accurate method of transfer dosimetry in the industrial (kGy) dose range. It is well established for calibrating industrial radiation sources against national standards (NIST, IAEA, NPL) and for comparisons between national laboratories. The accuracy of the method is generally very high, largely due to the low sensitivity of the alanine response to irradiation variables (energy, dose rate, temperature, etc.), and the ability of ESR spectrometers to measure dosimeter signals very precisely. As a matter of fact, the main requirements for a suitable system such as: linear response to dose, sensitivity, tissue equivalence, absence of energy dependence, absence of fading, small dimensions, ruggedness, and nondestructive readout, to a large extent are met by the alanine/ESR dosimetry. Here we analyzed the performances of two different alanine/ESR systems (3 mm pellets and 0.1 mm films) irradiated with therapy proton beams (62 MeV). The LET dependence of the response was obtained from the analysis of pellet irradiated with a modulated beam. The energy dependence of the response was derived from the analysis of film stacks irradiated with pristine beams. Use of thin films allowed for a high resolution sampling of the proton slowing down mechanisms. Alanine measurements are compared with Markus parallel plate ionization chamber and are aided by Monte Carlo calculations for medical physics using GEANT4 code

Gel dosimeters for three-dimensional mapping of radiotherapy doses were introduced at Yale University in the mid-1980’s. Soon after, research and development in this field also started in Italy. Early work was done at the Istituto Superiore di Sanità, and at the Universities of Pisa and Milan. Several institutes now collaborate on this topic with the goal of developing new formulations of hydrogel matrices with improved characteristics of stability, sensitivity and spatial resolution compared to those of earlier Fricke-gel and polymer-gel systems. Contrary to earlier gels based on natural gelling agents, such as porcine skin gelatin and/or agarose, which suffer from limited batch -to-batch reproducibility, we chose to develop formulations based on synthetic poly vinyl alcohol chemically cross-linked with glutaraldehyde. Several gel formulations and production procedures were investigated and are illustrated. The properties of these gels were investigated through a variety of techniques, including curemetry to determine the influence of GTA concentration and temperature over gelation time as well as scanning optical absorption to determine the sensitivity of the detectors and the spatial stability of the response. Comparative results are presented for the formulations we investigated, including one that provides a lower detection limit in the order of 100 mGy and a linear respon se exceeding 30 Gy, which makes it suitable for the verification of complex 3D treatment plans. Compared to earlier version of the detectors, we also achieved a simplification of the manufacturing processes in order to facilitate the diffusion of this technology and its transition from the bench to the bedside

This presentation describes the assessment of the gamma rays spectrum and dose. Yhe result have been used to perform dosimetry in cell cultures for in-vitro BNCT studies.

The use of neutrons for cancer treatments has stimulated the research for beam characterization in order to optimize the therapy procedures in Neutron Capture Therapy (Altieri, 2008). Several research laboratories have shown an increasing interest aimed at extending the applicability of Electron Spin Resonance (ESR) dosimetry to radiotherapy with different types of radiation beams. In particular, ESR spectrometry provides absorbed dose measurements through the detection of the stable free radicals produced by ionizing radiations. The ESR dosimetric method has many advantages such as simple and rapid dose evaluation, the readout procedure is non-destructive, linear response of many organic and inorganic compounds (Baffa,2014). In this work we study the response of phenolic compounds with and without gadolinium addition for electron spin resonance (ESR) dosimetry exposed to a gamma and mixed (n, gamma) field mainly composed of thermal neutrons. The compound IRGANOX 1076 phenol gives a phenoxy radical stabilized by the presence of two bulky groups [3]. Moreover, its high molecular weight, the low volatility and the compatibility with the dosimeter binding material (paraffin) are advantages with respect to lower molecular weight phenols. In this work we report the ESR investigation of phenols pellets and thin films with and without Gd2O3 (5% by weight) exposed in the thermal column of the Triga Mark II reactor of LENA of Pavia. Thanks to their size, the phenolic films here presented are good devices for the dosimetry of beams with high dose gradient and which require accurate knowledge of the precise dose delivered. The choice of Gd as the additive nucleus has been made because we are interested in applications for mixed field (neutrons/photons) Gd-ESR dosimetry has an high neutron capture cross section and, furthermore, the high LET secondary particles release their energy entirely in the dosimeter. The low content of gadolinium guarantees a good tradeoff between the sensitivity to thermal neutrons. However, the use of gadolinium reduces or abolishes tissue equivalence because of its high atomic number (Marrale, 2015). The dosimetric features of these ESR dosimeters have been investigated. In particular, we analyzed the ESR spectra of these compounds and their dependence on microwave power and modulation amplitude, their response after gamma and neutron irradiations, the detection limits for both beam typologies, signal stability after irradiation. The results of ESR experiments are compared with Monte Carlo simulations aimed at obtaining information about the total dose measured by means of ESR dosimeters.

The main gol of the present work is to investigate the response behaviour of alanine EPR pellets in clinical proton anc carbon ion beams. Proton irradiations were carried out at PSI (Switzerland) using both passive and active scattering modality, whereas, C ions irradiation were performed at GSI (Germany) adopting the raster scanning modality.

In this work we have studied the response of alanine pellets with and without gadolinium exposed to the thermal column of the TRIGA Mark II research reactor at the University of Mainz