Sviluppo di un metodo di radioterapia adattativa tramite immagini portali e Cone-Beam CT

Il presente lavoro, svolto presso il servizio di Fisica Sanitaria dell’Azienda Ospedaliera Universitaria di Parma, consiste nello sviluppo di un metodo innovativo di radioterapia adattativa. Il metodo è stato applicato a pazienti affetti da varie patologie, trattati con tecnica VMAT, (Volumetric Modulated Arc Therapy), altamente conformata al target. Il metodo sviluppato si compone di due fasi: nella prima fase vengono effettuate due analisi su immagini portali, di ricostruzione della dose all'isocentro e l'analisi gamma 2D. Se almeno una di queste fallisce, si interviene con la seconda fase, che vede l'acquisizione della CBCT del paziente e la taratura in densità elettronica della stessa. Si calcola dunque il piano su CBCT, previa operazione di contouring da parte del medico e, infine, si esegue l'analisi gamma 3D sulle matrici di dose calcolate sulla CT e sulla CBCT del paziente, quantificando gli indici gamma sulle strutture PTV, CTV e OAR di interesse clinico. In base ai risultati, se necessario, si può intervenire sul piano di trattamento. Le analisi gamma 2D e 3D sono state svolte avvalendosi di un software toolkit chiamato GADD-23 (Gamma Analysis on 2D and 3D Dose Distributions) implementato e sviluppato appositamente in ambiente Matlab per questo lavoro di tesi; in particolare, la realizzazione di GADD-23 è stata resa possibile grazie all'interazione con due software di tipo open-source, Elastix e CERR, specifici per l’elaborazione e la registrazione di immagini mediche. I risultati ottenuti mostrano come il metodo sviluppato sia in grado di mettere in luce cambiamenti anatomici che alcuni pazienti hanno subìto, di tipo sistematico, in cui è possibile prendere in considerazione una ripianificazione del trattamento per correggerli, o di tipo casuale, sui quali può essere utile condurre l'attenzione del medico radioterapista, sebbene non sia necessario un replanning.

Pulse shape studies of neutral particles with a liquid scintillator

The hadrontherapy exploits beams of charged particles against deep cancers. These ions have a depth-dose profile in which there is a little release of energy at the beginning of their path, whereas there is a sharp maximum, the Bragg Peak, near its end path. However, if heavy ions are used, the fragmentation of the projectile can happen and the fragments can release some dose outside the treatment volume beyond the Bragg peak. The fragmentation process takes place also when the Galactic Cosmic Rays at high energy hit the spaceship during space missions. In both cases some neutrons can be produced and if they interact with the absorbing materials nuclei some secondary particles are generated which can release energy. For this reason, studies about the cross section measurements of the fragments generated during the collisions of heavy ions against the tissues nuclei are very important. In this context, the FragmentatiOn Of Target (FOOT) experiment was born, and aims at measuring the differential and double differential fragmentation cross sections for different kinetic energies relevant to hadrontherapy and space radioprotection with high accuracy. Since during fragmentation processes also neutrons are produced, tests of a neutron detection system are ongoing. In particular, recently a neutron detector made up of a liquid organic scintillator, BC-501A with neutrons/gammas discrimination capability was studied, and it represents the core of this thesis. More in details, an analysis of the data collected at the GSI laboratory, in Darmstadt, Germany, is effectuated which consists in discriminating neutral and charged particles and then to separate neutrons from gammas. From this analysis, a preliminary energy-differential reaction cross-section for the production of neutrons in the 16O + (C_2H_4)_(n) and 16O + C reactions was estimated.

Analysis of fragmentation cross sections of GSI 2021 data for the FOOT experiment

Hadrontherapy is a medical treatment based on the use of charged particles beams accelerated towards deep-seated tumors on clinical patients. The reason why it is increasingly used is the favorable depth dose profile following the Bragg Peak distribution, where the release of dose is almost sharply focused near the end of the beam path. However, nuclear interactions between the beam and the human body constituents occur, generating nuclear fragments which modify the dose profile. To overcome the lack of experimental data on nuclear fragmentation reactions in the energy range of hadrontherapy interest, the FOOT (FragmentatiOn Of Target) experiment has been conceived with the main aim of measuring differential nuclear fragmentation cross sections with an uncertainty lower than 5\%. The same results are of great interest also in the radioprotection field, studying similar processes. Long-term human missions outside the Earth’s orbit are going to be planned in the next years, among which the NASA foreseen travel to Mars, and it is fundamental to protect astronauts health and electronics from radiation exposure .\\ In this thesis, a first analysis of the data taken at the GSI with a beam of $^{16}O$ at 400 $MeV/u$ impinging on a target of graphite ($C$) will be presented, showing the first preliminary results of elemental cross section and angular differential cross section. A Monte Carlo dataset was first studied to test the performance of the tracking reconstruction algorithm and to check the reliability of the full analysis chain, from hit reconstruction to cross section measurement. An high agreement was found between generated and reconstructed fragments, thus validating the adopted procedure. A preliminary experimental cross section was measured and compared with MC results, highlighting a good consistency for all the fragments.