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We report a study of the dosimetric features of phenolic compounds for applications in radiation therapy dosimetry of clinical photon beams by using ESR spectroscopy. After the optimization of the ESR readout parameters, basic dosimetric properties (such as intra-batch reproducibility, dose-response, sensitivity, linearity, dose rate dependence, tissue-equivalence and signal stability) of laboratory-made phenolic dosimeters in form of pellets were investigated. Furthermore, these dosimeters were tested for measuring the depth dose profile of a 6 MV clinical photon beam. The results reported show that these dosimeters are promising materials for ESR dosimetric applications in radiation therapy.

La radioterapia stereotassica extra-cranica (Stereotactic Body Radiation Therapy) consente di somministrare una dose ablativa ad un volume bersaglio non encefalico mediante un numero ridotto di frazioni. La riduzione nel numero di frazioni comporta necessariamente un aumento della precisione ed accuratezza in tutte le fasi del trattamento, dalla simulazione CT alla pianificazione ed all’erogazione della dose terapeutica. Dal punto di vista dosimetrico i trattamenti SBRT sono caratterizzati innanzitutto da un elevato grado di conformazione e soprattutto dalla presenza di gradienti di dose particolarmente ripidi necessari per minimizzare la dose ai tessuti sani circostanti ed agli organi a rischio posti nelle vicinanze del volume da irradiare. A seconda dello scenario clinico vengono utilizzate tecniche 3D-CRT (3D-Conformal Radiation Therapy) o IMRT (Intensity Modulated Radiotherapy). Questo lavoro mette a confronto, nel caso di irradiazione polmonare, due diverse tecniche ad intensità modulata: una tecnica statica Step-and-Shoot ed una tecnica volumetrica dinamica, la Tomoterapia Elicoidale (HT, Helicoidal TomoTherapy).

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. 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. The irradiation with mixed (neutron-gamma) field were performed within the thermal column of the TRIGA reactor, University of Pavia. Dosimeters readout was performed through the Electron Spin Resonance (ESR) 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.

The development of Neutron Capture Therapy (NCT) for cancer treatments has stimulated the research for beam characterization in order to optimize the therapy procedures. The NCT has found to be promising for treatments of tumours which hardly can be treated with other techniques, such as gliomas. Alongside with the improvements of this technique, the development of procedures for the beam characterization arouses great interest in order to optimize the therapy protocol by reliably determining the various (neutronic and photonic) components of the mixed beam usually employed for therapy. Electron Paramagnetic Resonance (EPR) dosimetry for electron and photon beams with alanine has attracted the attention of many research groups for dosimetric purposes. Furthermore, the applications of EPR dosimetry for high LET radiation beams, such as carbon ions and neutrons, are continuously increasing. This is because of the very good dosimetric features of alanine EPR detectors such as: tissue equivalence for photon beams, linearity of its dose-response over a wide range, high stability of radiation induced free radicals, no destructive read-out procedure, no need of sample treatment before EPR signal measurement and low cost of the dosimeters. Moreover, in order to improve the sensitivity to thermal neutrons of alanine dosimeters the addition of nuclei such as gadolinium oxidewas previously studied. 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 neighbourhood of the reaction site. In particular, it was found that low concentration (i.e. 5% by weight) of gadolinium oxide brings about an neutron sensitivity enhancement of more than 10 times without heavily reducing tissue equivalence. 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. Pure alanine dosimeters used were produced by Synergy Health (Germany) whereas the Gd-added dosimeters were produced at the University of Palermo. The irradiations were performed inside polyethylene holders to guarantee charged particles equilibrium conditions. The results of EPR experiments are compared to Monte Carlo (MC) simulations aimed at obtaining information about the contribution of the various components to the total dose measured by means of EPR dosimeters. For alanine dosimeters a good agreement between experimental data and MC simulation have been achieved.

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

Negli ultimi anni il crescente interesse verso la radioterapia a cattura neutronica (internazionalmente nota come Neutron Capture Therapy - NCT) per il trattamento di neoplasie ha stimolato diverse attività di ricerca finalizzate alla caratterizzazione del fascio utilizzato e all'ottimizzazione delle procedure radioterapiche. Tra i vari sistemi dosimetrici trovano largo impiego i rivelatori a stato solido ESR (Risonanza di Spin Elettronico) a base di alanina che presentano diversi vantaggi come la tessuto equivalenza, la linearità della risposta in un ampio intervallo di dose, l'elevata stabilità dei radicali liberi radioindotti, la non distruttività della lettura del dosimetro e il basso costo dei dosimetri. Queste caratteristiche, se associate alla possibilità di riconoscere le varie componenti di un campo misto di radiazione (neutroni e fotoni), rendono l'alanina un ottimo candidato per le dosimetria in tali campi. In questo lavoro vengono presentate le procedure seguite per la determinazione della componente fotonica nel campo di radiazione mista all'interno della colonna termica del reattore TRIGA dell'Università degli Studi di Pavia (dedicata ad attività sperimentali su Boron Neutron Capture Therapy - BNCT) mediante letture ESR di dosimetri di alanina. I dosimetri di alanina utilizzati sono stati irradiati in tre differenti posizioni all'interno della colonna termica; inoltre, per evitare l'uso di portacampioni contenenti idrogeno gli irraggiamenti, sono stati eseguiti all'interno di fantocci di grafite. Le misure ESR sono state effettuate mediante spettrometro Bruker ECS106 situato presso il Laboratorio di Dosimetria ESR/TL del Dipartimento di Fisica e Chimica dell'Università degli Studi di Palermo. Al fine di isolare la componente fotonica del campo misto sono stati effettuati due tipi di irraggiamento: all'interno di un box di carbonato di litio e al di fuori di esso. Sono state realizzate anche analisi Monte Carlo con il codice MCNP simulando le opportune geometrie del set-up sperimentale di irraggiamento. Questo tipo di analisi ha permesso di acquisire informazioni sui contributi delle varie componenti presenti nel campo misto. I valori sperimentali sono confrontati con le simulazioni Monte Carlo e i risultati sono stati discussi sulla base delle caratteristiche del campo misto e sulla risposta dei dosimetri di alanina alle radiazioni a diverso LET.

In the last decades 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. ESR is a spectroscopic method for investigating the structure and dynamics of such paramagnetic species. 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 energy released inside in the medium and this allows for dosimetric measurements through ESR technique which able to quantitatively determine the radical concentration. The use of alanine as a dosimetric material gave the possibility to apply ESR spectroscopy for high-dose standardization and dose control in radiation processing. 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. ESR detectors show a behavior that suggest possible applications for various kinds of beams used for radiation therapy. Nowadays, the most widely used organic compound as a dosimeter is the alanine. However, many researches are in progress with the aim at improving sensitivity of ESR dosimetry for doses much smaller than 1 Gy. More sensitive materials than alanine are needed to make the ESR dosimeter competitive with other dosimetry systems. 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. 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 radical can be improved by adding other alkyl chains which can be attached to the benzene ring. In particular, the phenol octadecyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate gave interesting results. Moreover, its high molecular weight, the low volatility and the compatibility with the dosimeter binding material (wax) are advantages with respect to lower molecular weight phenols. In this work we report the ESR investigation of phenols exposed to clinical photon and electron beams. The dosimetric features of these ESR dosimeters (dependence on microwave power and modulation amplitude, their response after gamma and electron irradiations, dependence on beam type and energy, the detection limits for both beam typologies, signal stability after irradiation) were investigated and the results are reported.

Negli ultimi anni è cresciuto il rischio di esposizioni radiologiche non controllate della popolazione, sia a causa di incidenti associati ad applicazioni industriali e mediche delle radiazioni ionizzanti sia in seguito ad incidenti legati all’abbandono o alla dismissione di sorgenti ma anche ad un uso criminale di materiale radioattivo [1–3]. Gli effetti biologici prodotti dalle radiazioni ionizzanti dipendono fortemente dalla quantità di energia impartita per unità di massa (dose assorbita) [4]. Pertanto, nell’ambito di un incidente radiologico, disporre di procedure di ricostruzione della dose assorbita da un individuo può contribuire oltre che ad identificare i membri della popolazione eventualmente coinvolti anche a stimare la gravità del danno subito. Inoltre per prevedere i possibili effetti a lungo termine e programmare un corretto trattamento terapeutico può essere altresì importante conoscere la distribuzione di dose al corpo [5, 6]. Poiché la popolazione comune non indossa dosimetri individuali specifici, diviene indispensabile la ricerca di dosimetri di emergenza tra i materiali facilmente reperibili sulla persona esposta o sul luogo dell’evento. I dosimetri fortuiti devono essere di facile acquisizione, semplici da preparare per le misure ed è auspicabile che l’intera procedura per la ricostruzione della dose in condizioni di emergenza sia rapida e non invasiva. É importante, inoltre, che la loro lettura sia sufficientemente sensibile da permettere la misura di dosi clinicamente significative (sicuramente inferiori ai 10 Gy) e la differenziazione tra valori di dose appartenenti ai diversi intervalli di dose di interesse per la dosimetria in caso di emergenza radiologica [7, 8]. L’insieme delle misure finalizzate alla ricostruzione della dose ricevuta in un passato recente o lontano vengono descritte collettivamente come dosimetria retrospettiva [6]. Si parla di dosimetria retrospettiva accidentale qualora le valutazioni siano mirate a ricostruire dosi ricevute in seno ad incidenti ai quali è associata emissione di radiazioni ionizzanti. Spesso le esposizioni accidentali dei membri della popolazione sono localizzate o comunque molto eterogenee. In tal caso, può essere utile adottare come dosimetri accidentali oggetti prossimi a diverse parti del corpo così da poter ricostruire la distribuzione di dose al corpo stesso. Per tale motivo vari tipi di materiali organici ed inorganici, prelevabili direttamente dagli individui o da oggetti in loro stretta prossimità, sono stati sottoposti ad esperimenti, anche con più tecniche sperimentali, per studiarne le potenzialità come dosimetri individuali fortuiti. Sono state prese in considerazione tecniche di dosimetria biologica e di dosimetria fisica. Queste ultime, in particolare, consentono una misura indiretta della dose tramite valutazione degli effetti fisici indotti dalle radiazioni ionizzanti. Tra le varie tecniche di dosimetria fisica, la spettroscopia di risonanza di spin elettronico (ESR) permette la valutazione quantitativa della concentrazione delle specie paramagnetiche radioindotte che è strettamente legata alla dose assorbita. Invece, la termoluminescenza (TL) fornisce informazioni sulla dose di irraggiamento tramite la misura della concentrazione di elettroni indotti dalla radiazione ionizzante nelle trappole della struttura di materiali isolanti o semiconduttori. L’obiettivo di questo lavoro è l'analisi delle proprietà dosimetriche campioni di vetro minerale, quale quello presente sui quadranti degli orologi da polso, irradiati con fasci di fotoni tramite spettroscopia EPR e tecnica TL.

La radioattività delle famiglie di radionuclidi naturali contenuti nei materiali da costruzione è responsabile in una certa misura dell'equivalente di dose riferibile al fondo naturale delle radiazioni. Tale radioattività contribuisce a due fattori di dose: la dose gamma esterna e la dose alfa interna legata all'introduzione e all'accumulo del radon nonché ad un contributo dovuto all’inalazione di polveri nelle quali le concentrazioni dei capostipiti naturali sono alte. I materiali da costruzione sono la sorgente principale del rateo di dose gamma nelle abitazioni. Tutti gli edifici in pietra contengono nuclei radioattivi come 226Ra, 232Th e 40K. É noto che i livelli di radon sono legati al radio intrappolato nei grani del materiale lapideo. Negli edifici con alti livelli di radio l'esalazione di radon può diventare di grande importanza. La conoscenza dei livelli di radioattività nei materiali da costruzione è perciò importante nel definire il rischio radiologico per la salute umana. La Sicilia è un'isola con caratteristiche geologiche e litologiche specifiche. Ogni litologia presenta diverse concentrazioni di radionuclidi. Questo diventa importante sia nel caso di costruzioni in pietra che di materiali ottenuti da malte e cementi ottenuti da miscelazione dei materiali provenienti da diverse cave.

The optimization of the procedures of Neutron Capture Therapy (NCT) for cancer treatments involves research for beam characterization. One major issue for this therapy is the reliable dosimetric determination of the various (neutronic and photonic) components of the employed beam. In particular, the precise and accurate measurements of the gamma photon component is fundamental for evaluating the risks to healthy tissues hit by the mixed field. Among solid state dosimeters the alanine detectors read by Electron Paramagnetic Resonance (EPR) technique present several advantages such as: tissue equivalence for photon and electron beams, 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 and low cost of the dosimeters. These features associated with the possibility of recognizing the various components of a mixed radiation fields makes alanine a good candidate for dosimetry in neutron-gamma fields. In this work we determine the gamma component of the mixed radiation field in thermal column of the Triga Reactor of University of Pavia (which is used for experimental activities on NCT) by means of alanine EPR dosimeters. Commercial alanine dosimeters produced by Synergy Health (Germany) were exposed in three positions in the thermal column; the irradiations were performed inside graphite holders to avoid use of hydrogenous phantoms for minimizing the gamma contribution due to the plastic holders. EPR measurements were carried out through Bruker ECS106 spectrometer equipped with a TE102 rectangular cavity. In order to isolate the gamma components of the mixed field two kinds of irradiations were carried out inside a lithium carbonate box (wherein the thermal neutron component is heavily reduced) and outside of it. MCNP Monte Carlo simulations of the irradiation set-up were carried out, calculating the contributions of the various components present in the mixed field (thermal and fast neutron and gamma). The experimental values are compared with the computations of the Monte Carlo simulations and the results are discussed on the basis of the mixed field features and on the response of alanine dosimeters to high and low LET radiations.

In the last decades several research laboratories have shown an increasing interest aimed at extending the applicability of Electron Paramagnetic Resonance (EPR) dosimetry to radiotherapy with different types of radiation beams. EPR is a spectroscopic method for investigating the structure and dynamics of such paramagnetic species. 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 energy released inside in the medium and this allows for dosimetric measurements through EPR technique. The use of alanine as a dosimetric material gave the possibility to apply EPR spectroscopy for high-dose standardization and dose control in radiation processing (Marrale 2016). The EPR 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. EPR detectors show a behavior that suggest possible applications for various kinds of beams used for radiation therapy. Nowadays, the most widely used organic compound as a dosimeter is the alanine. However, many researches are in progress with the aim at improving sensitivity of EPR dosimetry for doses much smaller than 1 Gy. More sensitive materials than alanine are needed to make the EPR dosimeter competitive with other dosimetry systems. Our research group has started an investigation of the EPR response of some phenols compounds for possible EPR dosimetric applications suitable features, such as high efficiency of radiation-matter energy transfer and radical stability at room temperature. 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 radical can be improved by adding other alkyl chains which can be attached to the benzene ring. The phenol octadecyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate gave interesting results. Moreover, its high molecular weight, the low volatility and the compatibility with the dosimeter binding material (wax) are advantages with respect to lower molecular weight phenols. In this work we report the EPR investigation of phenols exposed to clinical photon and electron beams (Gallo, 2016). The dosimetric features of these EPR dosimeters (dependence on microwave power and modulation amplitude, their response after gamma and electron irradiations, dependence on beam type and energy, the detection limits for both beam typologies, signal stability after irradiation) were investigated and the results are reported.

Along with the Neutron Capture Therapy (NCT) development and with the use of thermal neutrons for radiotherapeutic purposes, many efforts have been devoted to the beam characterization in order to optimize the therapy procedures. Reliable dosimetric measurements should be able to determine the various components (neutronic and photonic) of the mixed beam usually employed for therapy. We have studied the effect of the additive such as gadolinium and 10B-boric acid on the neutron sensitivity of alanine ESR dosimeters exposed to a gamma and mixed (n, gamma) field mainly composed by thermal neutrons. We have chosen both this additive nuclei because of their very high capture cross section to thermal neutrons. Furthermore, in the nuclear reaction with thermal neutrons particle, which in turn release their energy in the neighbourhood of the reaction site, are ejected. We completed our study through a Monte Carlo simulation aimed at obtaining information about the reliability of this powerful tool in predicting the response enhancement achievable with the addition of gadolinium and 10B-boric acid in alanine dosimeters. These computational values obtained through simulation are compared with the experimental results.

Along with the Neutron Capture Therapy (NCT) development and with the use of thermal neutrons for radiotherapeutic purposes, many efforts have been devoted to the beam characterization in order to optimize the therapy procedures. Reliable dosimetric measurements should be able to determine the various components (neutronic and photonic) of the mixed beam usually employed for therapy [1]. We have studied the effect of the additive such as gadolinium and 10B-boric acid on the neutron sensitivity of alanine ESR dosimeters exposed to a gamma and mixed (n, gamma) field mainly composed by thermal neutrons. We have chosen both this additive nuclei because of their very high capture cross section to thermal neutrons. Furthermore, in the nuclear reaction with thermal neutrons particles, which in turn release their energy in the neighbourhood of the reaction site, are ejected [2]. We completed our study through a Monte Carlo simulation aimed at obtaining information about the reliability of this powerful tool in predicting the response enhancement achievable with the addition of gadolinium and 10B-boric acid in alanine dosimeters. These computational values obtained through simulation are compared with the experimental results.

Heavy-ions beams offer several advantages compared to other radiation such as low lateral scattering and high biological effectiveness (RBE) in the Bragg peak region, making them particularly attractive for the treatment of radio-resistant tumors localized close to organs at risk [1]. Although ion beam radiotherapy ultimately requires dose prescription in terms of biological dose or cell survival, absorbed dose is still the quantity mostly used in clinical quality assurance and to dosimetrically characterize the beam. Moreover, the nuclear projectile fragmentation of heavy ions because of inelastic nuclear interactions with medium produces secondary particles with lower Z. The detailed knowledge of the resulting mixed radiation field at each point of the treatment area is crucial for an accurate estimate of the biological dose. Among solid state detectors the alanine EPR 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. These features associated with the possibility of recognizing the various components of a mixed radiation fields makes alanine a good candidate for Quality Assurance of clinical particle beams [2] and also for dosimetry in space radiation. The main goal of the present work is to investigate the response behaviour of alanine EPR pellets in clinical carbon ion beams. In particular, alanine dose response at selected locations within a carbon ion radiation field has been measured with alanine dosimeters in water and in presence of medium inhomogeneities (such as bone-water) to simulate different quasi-clinical scenarios. Furthermore, we aim at understanding the influence of fading and the variations in the shape and the power saturation characteristics of the EPR signal in alanine pellets exposed to different carbon ions LET.

Heavy-ions beams offer several advantages compared to other radiation such as low lateral scattering and high biological effectiveness (RBE) in the Bragg peak region, making them particularly attractive for the treatment of radio-resistant tumours localized close to organs at risk [1]. The extension of ion therapy to new clinical cases requires the exploitation of a dedicated treatment planning system (TPS) based on the existing version of TRiP98 [2,3], established TPS for carbon ions. The theoretical models and experimental databases included in TRiP98 are presently mainly based on measurements in water. This approximation can be applied successfully to reproduce many biological tissues with the exception of bones, where the presence of heavy elements, like calcium, might change significantly the composition of the resulting mixed radiation field. Presently, the TriP98 physical beam model takes into account for the bone only its density variation, but it neglects difference between bones and water in attenuation of the primary and production of secondary particles through nuclear fragmentation. However, a detailed knowledge of the particle field at each point of the treatment area is crucial for an accurate estimate of the actual dose. A previous study [4] investigated the influence of different types of bone on the carbon particles range. In the present work we aim at understanding the influence of medium inhomogeneities on the 12C beam dose distribution. For the experiment, a bone target was placed inside a water phantom. The irradiation of the target volume positioned partially behind the bone target and partially directly in water was simulated with TRiP98 and the dose at the interface measured at several depths along the primary beam direction. Absolute dose measurements were achieved with a system of pin-point ionization chambers, while the relative dose distribution was investigated with two different solid states detectors: thermoluminescence detectors of type TLD-700 and alanine ESR pellets. The position of the target volume, the thickness and the type of bone were changed to investigate the influence of the inhomogeneity in different quasi-clinical scenarios. The experimental results were compared with the values predicted by TRiP98.

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.

There is a need for a sensitive dosimeter using Electron Spin Resonance spectroscopy for use in medical applications, since non-destructive read-out and dose archival could be achieved with this method. This work reports a systematic ESR investigation of IRGANOX ® 1076 exposed to clinical electron beams produced by a LINAC used for radiation therapy treatments. Recently, dosimetric features of this material were investigated for irradiation with 6 0Co γ -photons and neutrons in both pellet and film shape and have been found promising thanks to their high efficiency of radiation-matter energy transfer and radical stability at room temperature. Here the analysis of the dosimetric features of these ESR dosimeters exposed to clinical electron beams at energies of 7, 10 and 14 MeV, is described in terms of dependence on microwave power and modulation amplitude, response on dose, dependence on beam type, detection limits, and signal stability after irradiation. 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 minimum detectable dose is found to be smaller than 1 Gy. Comparison of electron stopping power values of these dosimeters with those of water and soft tissue highlights equivalence of the response to electron beams in the energy range considered. The signal intensity was monitored for 40 days after irradiation and for all energies considered and it shows negligible variations in the first 500 h after irradiation whereas after 1100 h the signal decay is only of about 4%. In conclusion, it is found that phenolic compounds possess good dosimetric features which make it useful as a sensitive dosimeter for medical applications.

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

This paper reports the preliminary results obtained by Electron Paramagnetic Resonance (EPR) measurements on films of IRGANOX® 1076 phenols with and without low content (5% by weight) of gadolinium oxide (Gd2O3) exposed in the thermal column of the Triga Mark II reactor of LENA (Laboratorio Energia Nucleare Applicata) of Pavia (Italy). 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 dependence of EPR signal as function of neutron dose was investigated in the fluence range between 10(11) cm(-2) and 10(14) cm(-2). Linearity of EPR response was found and the signal was compared with that of commercial alanine films. Our analysis showed that gadolinium oxide (5% by weight) can enhance the thermal neutron sensitivity more than 18 times. Irradiated dosimetric films of phenolic compound exhibited EPR signal fading of about 4% after 10 days from irradiation.

In this work we report some preliminary results regarding the analysis of electron paramagnetic resonance (EPR) response of alanine pellets and alanine pellets added with gadolinium used for dosimetry at the TRIGA research reactor in Mainz, Germany. Two set-ups were evaluated: irradiation inside PMMA phantom and irradiation inside boric acid phantom. We observed that the presence of Gd2O3 inside alanine pellets increases the EPR signal by a factor of 3.45 and 1.24 in case of PMMA and boric acid phantoms, respectively. We can conclude that in the case of neutron beam with a predominant thermal neutron component the addition of gadolinium oxide can significantly improve neutron sensitivity of alanine pellets. Monte Carlo (MC) simulations of both response of alanine and Gd-added alanine pellets with FLUKA code were performed and a good agreement was achieved for pure alanine dosimeters. For Gd2O3-alanine deviations between MC simulations and experimental data were observed and discussed.