The CNAO in Pavia, acronym of "Centro Nazionale di Adroterapia Oncologica", is the only italian centre that can provide oncological treatments through irradiation by protons and carbon ions beams accelerated through a synchrotron. The use of heavy charged particles for the treatment of tumors has many advantages related to traditional photon or electron radiotherapy. Due to the various interactions of hadrons with matter, it's possible to concentrate the total dose delivered in a very small spatial region and so to limit the energy release in surrounding healthy tissues. Moreover, due to their high LET (Linear Energy Transfer), the biological damage of heavy charged particle to cancer's cells is greater than the photons one. For this reason, the hadrontherapy performed with protons and carbon ions is particularly useful to treat local cancer volumes not surgically operable, radio-resistant or located close to radio-sensible organs. With this thesis work, conducted entirely at CNAO within the LM+ project promoted by the University of Studies of Pavia, I present the results obtained during the commissioning phase of the beam extraction with RF-knockout technique. Unlike the method currently used at CNAO, which excites a beam resonance through an acceleration process obtained by a particular magnetic circuit (betatron core), RF-knockout technique consist of a transverse beam perturbation which amplifies the transverse particle's motions and takes them in the extraction septum. The implementation of this alternative extraction technique has several advantages. First of all, requiring a bunched beam that occupies only part of the synchrotron, the RF-knockout extraction allows the implementation of a multi-acceleration system: once the dose indicated in the treatment plan for a particular energy has been reached, any charge left in the machine could be recycled and accelerated to the new energy required. Instead, the extraction with the betatron core requires a de-bunched beam that occupies the entire circumference. So, as the beam has to be bunched so that the radio-frequency is accelerating at every revolution and the confinement of the particles into the bunch leads to significant losses, this technique is not compatible with the multi-acceleration. Moreover, the RF-knockout permits to start and stop the extraction vary quickly and so it's particularly suitable every time that the irradiation has to be synchronized with the patient's breath. This theses is structured as it follows. In Chapter 1 there are basic informations on the interaction processes of hadrons with matter and on their clinical use for cancer treatments. Subsequently it's described CNAO's structure, paying particular attention to the accelerator's components. Chapter 2 deals with the problem of beam dynamics, deriving the equations that describe the motions of the particles in the transverse plane and in the longitudinal direction and obtaining the stability conditions. Chapter 3 is all dedicated to the theory of the Third Order Resonance and to its use in the phase of beam extraction from the synchrotron. In Chapter 4, after a first part in which the various existent extraction methods are described, the extraction process with RF-knockout is analyzed in detail, focusing in particular on the various parameters to take into account and on their effects on the beam. In Chapters 5 and 6 the method followed is described, the different types of measurements carried out are analyzed and the original and more significant results obtained during the studies with protons and carbon ions are presented.
Il CNAO di Pavia, acronimo di Centro Nazionale di Adroterapia Oncologica, è l'unico centro in Italia in grado di fornire trattamenti oncologici mediante irraggiamento con fasci di protoni e ioni carbonio accelerati per mezzo di un sincrotrone. L'impiego delle particelle cariche pesanti per la cura di tumori presenta diversi vantaggi rispetto alla radioterapia convenzionale a fotoni o elettroni. Le diverse modalità di interazione degli adroni con la materia permettono infatti di concentrare la dose depositata in regioni molto ristrette e di limitare il rilascio di energia nei tessuti sani circostanti. Inoltre, grazie al loro LET (Linear Energy Transfer) elevato, il danno biologico arrecato dalle particelle cariche pesanti alle cellule tumorali risulta maggiore rispetto a quello dovuto ai fotoni. Per questi motivi, l'adroterapia con protoni e ioni carbonio risulta particolarmente efficace nel trattamento di tumori localizzati inoperabili, radioresistenti o localizzati in prossimità di organi radiosensibili. Con questo lavoro di tesi, condotto interamente presso il CNAO nell'ambito del progetto LM+ promosso dall'Università degli Studi di Pavia, si intendono presentare i risultati conseguiti nella fase di commissioning dell'estrazione del fascio con tecnica RF-knockout. A differenza del metodo attualmente impiegato a CNAO, che consiste nel condurre il fascio in risonanza tramite un processo di accelerazione ottenuto con un particolare circuito magnetico (betatron core), la tecnica RF-knockout prevede di perturbare il fascio trasversalmente in modo da amplificarne i moti trasversali e condurlo all'interno del setto di estrazione. L'impiego di questa tecnica di estrazione alternativa prevede diversi vantaggi. In primo luogo, richiedendo un fascio impulsato (bunched) che occupa solamente parte del sincrotrone, l'RK-knockout permette l'implementazione di un sistema di multi-accelerazione: raggiunta la dose prevista dal piano di trattamento per una determinata energia, l'eventuale carica rimasta in macchina può essere riciclata e accelerata alla nuova energia richiesta. L'estrazione con betatron core richiede invece un fascio continuo (debunched) che occupa l'intera circonferenza, e quindi, dato che il fascio deve essere impulsato affinché la radiofrequenza risulti accelerante ad ogni rivoluzione e poiché il processo di intrappolamento comporta perdite significative, non risulta compatibile con la multi-accelerazione. L'RF-knockout consente inoltre di interrompere e riprendere l'estrazione in tempi molto brevi e risulta pertanto particolarmente indicata in tutti i casi in cui l'erogazione del fascio deve essere sincronizzata con il respiro del paziente. Questo lavoro di tesi è strutturato come segue. Nel Capitolo 1 sono fornite informazioni di base sull'interazione degli adroni con la materia e sul loro impiego in ambito clinico per il trattamento di tumori. Successivamente viene descritta la struttura del CNAO, soffermandosi sui diversi componenti che costituiscono l'acceleratore. Nel Capitolo 2 si affronta il problema della dinamica del fascio, ricavando le equazioni che descrivono il moto delle particelle nel piano trasversale e in direzione longitudinale e ottenendo le condizioni di stabilità. Il Capitolo 3 è interamente dedicato alla teoria della risonanza al terz'ordine e al suo impiego nella fase di estrazione del fascio dal sincrotrone. Nel Capitolo 4, dopo una prima fase in cui vengono brevemente descritti i diversi metodi di estrazione esistenti, si analizza nel dettaglio il processo di estrazione con tecnica RK-knockout, soffermandosi in particolar modo sui vari parametri da tenere in considerazione e sui loro effetti sul fascio. Nei Capitoli 5 e 6 viene descritta la linea seguita durante la fase di commissioning, sono analizzate le diverse tipologie di misure effettuate e si riportano i risultati originali e maggiormente significativi conseguiti rispettivamente durante gli studi con protoni e con ioni carbonio.
Commissioning dell'estrazione del fascio di protoni e ioni carbonio con tecnica RF-knockout al Centro Nazionale di Adroterapia Oncologica di Pavia
MELIGA, PAOLO
2018/2019
Abstract
The CNAO in Pavia, acronym of "Centro Nazionale di Adroterapia Oncologica", is the only italian centre that can provide oncological treatments through irradiation by protons and carbon ions beams accelerated through a synchrotron. The use of heavy charged particles for the treatment of tumors has many advantages related to traditional photon or electron radiotherapy. Due to the various interactions of hadrons with matter, it's possible to concentrate the total dose delivered in a very small spatial region and so to limit the energy release in surrounding healthy tissues. Moreover, due to their high LET (Linear Energy Transfer), the biological damage of heavy charged particle to cancer's cells is greater than the photons one. For this reason, the hadrontherapy performed with protons and carbon ions is particularly useful to treat local cancer volumes not surgically operable, radio-resistant or located close to radio-sensible organs. With this thesis work, conducted entirely at CNAO within the LM+ project promoted by the University of Studies of Pavia, I present the results obtained during the commissioning phase of the beam extraction with RF-knockout technique. Unlike the method currently used at CNAO, which excites a beam resonance through an acceleration process obtained by a particular magnetic circuit (betatron core), RF-knockout technique consist of a transverse beam perturbation which amplifies the transverse particle's motions and takes them in the extraction septum. The implementation of this alternative extraction technique has several advantages. First of all, requiring a bunched beam that occupies only part of the synchrotron, the RF-knockout extraction allows the implementation of a multi-acceleration system: once the dose indicated in the treatment plan for a particular energy has been reached, any charge left in the machine could be recycled and accelerated to the new energy required. Instead, the extraction with the betatron core requires a de-bunched beam that occupies the entire circumference. So, as the beam has to be bunched so that the radio-frequency is accelerating at every revolution and the confinement of the particles into the bunch leads to significant losses, this technique is not compatible with the multi-acceleration. Moreover, the RF-knockout permits to start and stop the extraction vary quickly and so it's particularly suitable every time that the irradiation has to be synchronized with the patient's breath. This theses is structured as it follows. In Chapter 1 there are basic informations on the interaction processes of hadrons with matter and on their clinical use for cancer treatments. Subsequently it's described CNAO's structure, paying particular attention to the accelerator's components. Chapter 2 deals with the problem of beam dynamics, deriving the equations that describe the motions of the particles in the transverse plane and in the longitudinal direction and obtaining the stability conditions. Chapter 3 is all dedicated to the theory of the Third Order Resonance and to its use in the phase of beam extraction from the synchrotron. In Chapter 4, after a first part in which the various existent extraction methods are described, the extraction process with RF-knockout is analyzed in detail, focusing in particular on the various parameters to take into account and on their effects on the beam. In Chapters 5 and 6 the method followed is described, the different types of measurements carried out are analyzed and the original and more significant results obtained during the studies with protons and carbon ions are presented.È consentito all'utente scaricare e condividere i documenti disponibili a testo pieno in UNITESI UNIPV nel rispetto della licenza Creative Commons del tipo CC BY NC ND.
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https://hdl.handle.net/20.500.14239/19611