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Monte-Carlo optimization of beam properties and dose conformation of small field proton therapy beamlines for beyond state-of-the-art eye treatment

par Gnacadja, Sédjio Eustache
Président du jury Labeau, Pierre-Etienne
Promoteur Pauly, Nicolas
Co-Promoteur Hernalsteens, Cédric
Publication Non publié, 2023-10-27

Thèse de doctorat

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Résumé :

Eye cancer encompasses a group of rare malignant tumors that greatly impact the quality oflife of affected patients. Late detection and management at an advanced stage are the leadingcauses of this impact, as eye cancer cells often silently proliferate for years before exhibitingsymptoms. Ion therapy represents a less aggressive alternative to other treatment methodsfor eye cancer, offering a higher chance of preserving both the affected eye and the patient’svision. One key aspect of ion therapy facilities dedicated to eye cancer treatment is their abilityto deliver the total dose of an individual session in an extremely short time, minimizing thepatient’s gazing time. Nevertheless, in most of these facilities, the beam experiences significantlosses during its production and transport to the treatment room, due to the substantial energydegradation required to achieve clinical ranges appropriate for treating ocular tumors. Forthis reason, satisfying the dose rate constraint while simultaneously fulfilling all the clinicalrequirements imposed on the dose deposition profiles poses a considerable challenge. Thegeneral objective of this thesis is to evaluate numerically and enhance the clinical propertiesachieved when treating ocular tumors using proton therapy facilities. In the first part of thework, we start by developing a numerical model of the passive scattering eye treatment beamlineof the proton therapy company Ion Beam Applications (IBA). Using this model, we conductedsimulations to assess its clinical properties, which were validated against experimental datafrom the Westdeutsches Protonentherapiezentrum Essen (WPE) proton therapy center in Essen.Based on this validation, we proposed modifications to the nozzle design, increasing the doserate by up to a factor of 3. Additionally, we explored the feasibility of reducing the dose outsidethe irradiation field through the use of an additional collimator adequately inserted inside ofthe nozzle. In the second part of the work, the emphasis was put to the treatment of oculartumors in pencil beam scanning mode, using a compact gantry proton therapy system. Morespecifically, we conducted a detailed study of the IBA Proteus One (P1) beamline and proposeda design of its nozzle to achieve clinical performance comparable to state-of-the-art passivescattering beamlines. Additionally, we re optimized the configuration of the magnets to allowthe use of a diamond degrader material instead of Beryllium at low energies, for an increaseddose rate of the system. The simulations demonstrate that the combination of the diamonddegrader with an additional quadrupole adequately positioned in the beamline increases theinstantaneous dose by up to a factor of 3, with a negligible impact on the clinical properties ofthe system. Overall, the results obtained in the two parts of the thesis highlight the importanceof numerical simulations toward the design, optimization of modern proton therapy systemsdedicated to ocular tumors treatment.