FEASIBILITY AND DOSIMETRIC CHARACTERIZATION OF SINGLE CONVERGENT BEAM TELETHERAPY DEVICE

RODOLFO FIGUEROA; MAURO VALENTE

Dublin

Congreso; European Congress of Medical Physics; 2014

European Federation of Organisations for Medical Physics

Background: Currently X-photons teletherapy utilizes divergent beams, which implies a non-negligible irradiation of healthy tissues. A convergent beam would allow a greater radiation focalization. This work aimed to determine feasibility and characteristics of a new type of radiation therapy based on the application of a convergent beam of photons, using a device capable of generating a convergent X-ray beam of energies. We named this technique RTHC. Materials and Methods: An analytical method was developed to determine dosimetric characteristics of an ideal convergent X photon beam in a hypothetical water phantom. Then, using Monte Carlo (MC) code, PENELOPE, an ideal convergent beam was applied to a water phantom using a specially adapted geometry; results were compared with those of the analytical method. MC simulations were performed in a vacuum, using a more realistic geometry. These simulations were performed for a largesize thin spherical anodic target (30 cm radius). Thus, the electrons perpendicularly impact upon various points of the cap (RTHC condition, convergent beam radiotherapy), mainly at the focal point in the water phantom center. The X radiation (bremsstrahlung) is generated toward the focus. A spherical collimator coaxial to the cap, with many holes, allows a clean convergent X-ray beam output. On the other hand, magnitudes of the electric / magnetic fields necessary for a clinical use electron beam (0.1 to 20 MeV) are determined using electromagnetism equations with relativistic corrections. Results: In-depth dose peaks similar in shape to hadron therapy were shown. This remarks that in-depth dose peaks are generated at the focus point/isocenter. The electric and magnetic fields needed to control the deflection of the electron beams in the RTHC geometry were calculated. Discussion: Results are consistent with those obtained with PENELOPE code. Peak-focus is independent of the X photon beam energy, though its intensity is not. Aperture angle at each impact point depends on the energy beam, the atomic Z number and the target thickness. Electric and magnetic fields necessary to control the X-ray beam are highly feasible by means of a specially designed electric/magnetic device. Electric fields are much more difficult to achieve than magnetic ones, especially at high energies. In conclusion, is possible to generate a device with the abovementioned characteristics (Pat.Pending-CoverayTM)