Hadrontherapy: Issues on therapy with ion beams

F. GESER; M. VALENTE

Temuco

Jornada; 5tas Jornadas de Fisica Medica en la Frontera; 2016

UFRO-SOFIMECH

p, li { white-space: pre-wrap; }Radiotherapy constitutes one of the most used tool for neoplastic diseases treatment for over a century. As every treatment developed so far, it has its advantages and disadvantages. For example, choosing small spatial regions for dose deposition is not trivial and the convergence often results in high secondary and not desired dose in the surrounding healthy biological tissue. To this end, it has been shown that charged massive particles such as protons, alpha particles or some other light ions (carbon ions, ¹²C), provides a highly spatial localization of the depth-dose curve, delivering most of its energy at the end of the path they traverse. This small region is called the Bragg Peak, and its theoretical understanding is crucial at the moment of developing treatment planning systems with high precision. Other physical process that needs accurate understanding is the nuclear fragmentation (in case of light ions), because they do deposit small amounts of dose beyond the Bragg Peak. Nevertheless, it is a known fact that at the Bragg Peak region, the biological efficiency (RBE) is enhanced respect to the photons RBE (a factor three for ¹²C). This kind of therapy is not thought of as a replacement of radiotherapy, but merely as a complement for the treatment of deep tumours.This work aims to describe the Bragg Peak and the associated parameter, the range of the charged particles. This must be known with an uncertainty of at most 1 mm. To this end, the theory of stopping power of charged particles in matter has been exhaustively studied and a review of important parameters (such as the mean ionization potential of the material) was carried out. A much more ambitious goal is to take advantage of other nuclear fragments (or possibly their decay products) for a real-time monitoring of the dose deposition in the patient. On the other hand, several tests were done to the Monte Carlo (MC) code FLUKA with the aim of using it as a Monte Carlo Treatment Planning system (MCTP). This is important because the code is able to generate a more realistic geometry of the patient´s body (by processing DICOM inputs), with the possibility of calculating 3D particle fluences, generation of mixed fields, and simulation of secondary on-line monitoring using positron emission tomography (PET). It also includes models to estimate the biological dose delivered respect to the physical dose typically calculated in other planning systems.