G.A. Pablo Cirrone

Preliminary investigation on the use of the MOSFET dosimeter in proton beams

Metal Oxide Semiconductor (MOS) device structures can be used to measure ionizing radiation through the mechanism of hole trapping in the oxide layer leading to changing of electrical characteristic of the device. They are a new type of direct reading semiconductor dosimeters. Due to their extremely small physical size, ability to permanently store the accumulated dose, dose-rate independence and their ease of use make them very promising for in vivo dosimetry. They are attractive for dosimetry in small radiation fields used in modern radiation oncology modalities, as conformal radiotherapy, IMRT, stereotactic radiotherapy/radiosurgery and proton therapy. Preliminary results on the use of commercial MOSFET dosimeters (TN-502RD, Thomson & Nielsen Electronics Ltd, Canada) irradiated on therapeutic 62 MeV proton beams are presented. Linearity with absorbed dose, sensibility and energy dependence were investigated. Moreover, the possibility to use of MOSFET dosimeters in order to measure the Output Factors (OF) for very small irradiation fields was verified. The comparison of OF obtained using MOSFETs and other dosimetry systems is reported.

Characterization of an in-beam PET prototype for proton therapy with different target composition

Positron emission tomography is a valuable method for in situ and non invasive monitoring of the accuracy of the treatment in hadron therapy. It takes advantage of short lived β+- emitters spontaneously produced in the biological tissues during irradiation, by means of projectile and/or target nuclei fragmentations. Although β+- emitter production cross-sections and hadron stopping power exhibit a different dependence on the hadron energy, it is still possible to extract non invasively in vivo information about dose localization reconstructing the distribution of positron annihilation points.

Residual energy measurements for proton computed tomography

We present a preliminary study on proton calorimetry for pCT (proton computed tomography) system. In a pCT scanner there are a tracking system for proton-path reconstruction and a calorimeter for measurement of residual proton energy. We set up a prototype system using a silicon tracker and a scintillator crystal . In particular, we show the measurements obtained with YAG:Ce scintillator crystal and therapeutic proton beams.

Proof-of-Principle results of proton computed tomography

A proof of principle proton Computed Tomography (pCT) apparatus, based on a silicon microstrip tracker and a YAG:Ce calorimeter, has been manufactured. Tests with a 175 MeV proton beam at The Svedberg Laboratory (TSL, Uppsala, Sweden) aiming at collecting data for reconstructing a tomographic image have been carried out. Algebraic iterative reconstruction methods, together with the most likely path formalism, have been used to obtain non-homogeneous phantom images to eventually extract density and spatial resolutions. The heavy computation load required by the algebraic algorithms has been approached fully exploiting the high calculation parallelism of Graphics Processing Units. The dose delivered to the phantom during the tomographic data-taking has been estimated as well as spatial and density resolutions dependence on dose. An upgraded pCT apparatus with an extended field-of-view able to reconstruct objects of the size of a human head, thus suitable to be used in pre-clinical tests, is now at an advanced construction stage. Using this new apparatus radiographies of an anthropomorphic phantom have been taken at the proton experimental beam line of the ‘Trento Proton Therapy Center’ (Trento, Italy).