Monia Vadrucci

Calibration of GafChromic EBT3 for absorbed dose measurements in 5 MeV proton beam and 60Co γ-rays

PURPOSE To study EBT3 GafChromic film in low-energy protons, and for comparison purposes, in a reference (60)Co beam in order to use it as a calibrated dosimetry system in the proton irradiation facility under construction within the framework of the Oncological Therapy with Protons (TOP)-Intensity Modulated Proton Linear Accelerator for RadioTherapy (IMPLART) Project at ENEA-Frascati, Italy. METHODS EBT3 film samples were irradiated at the Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali di Legnaro, Italy, with a 5 MeV proton beam generated by a 7 MV Van de Graaff CN accelerator. The nominal dose rates used were 2.1 Gy/min and 40 Gy/min. The delivered dose was determined by measuring the particle fluence and the energy spectrum in air with silicon surface barrier detector monitors. A preliminary study of the EBT3 film beam quality dependence in low-energy protons was conducted by passively degrading the beam energy. EBT3 films were also irradiated at ENEA-National Institute of Ionizing Radiation Metrology with gamma radiation produced by a (60)Co source characterized by an absorbed dose to water rate of 0.26 Gy/min as measured by a calibrated Farmer type ionization chamber. EBT3 film calibration curves were determined by means of a set of 40 film pieces irradiated to various doses ranging from 0.5 Gy to 30 Gy absorbed dose to water. An EPSON Expression 11000XL color scanner in transmission mode was used for film analysis. Scanner response stability, intrafilm uniformity, and interfilm reproducibility were verified. Optical absorption spectra measurements were performed on unirradiated and irradiated EBT3 films to choose the most sensitive color channel to the dose range used. RESULTS EBT3 GafChromic films show an under response up to about 33% for low-energy protons with respect to (60)Co gamma radiation, which is consistent with the linear energy transfer dependence already observed with higher energy protons, and a negligible dose-rate dependence in the 2-40 Gy/min range. Short- and long-term scanner stabilities were 0.5% and 1.5%, respectively; film uniformity and reproducibility were better than 0.5%. CONCLUSIONS The main purpose of this study was to implement EBT3 dosimetry in the proton low-energy radiobiology line of the TOP-IMPLART accelerator, having a maximum energy of 7 MeV. Low-energy proton and (60)Co calibrated sources were used to investigate the behavior of film response vs to be written in italicum dose. The calibration in 5 MeV protons is currently used for dose assessment in the radiobiological experiments at the TOP-IMPLART accelerator carried out at that energy value.

First acceleration of a proton beam in a side coupled drift tube linac

We report the first experiment aimed at the demonstration of low-energy protons acceleration by a high-efficiency S-band RF linear accelerator. The proton beam has been accelerated from 7 to 11.6 MeV by a 1 meter long SCDTL (Side Coupled Drift Tube Linac) module powered with 1.3 MW. The experiment has been done in the framework of the Italian TOP-IMPLART (Oncological Therapy with Protons-Intensity Modulated Proton Therapy Linear Accelerator for Radio-Therapy) project devoted to the realization of a proton therapy centre based on a proton linear accelerator for intensity modulated cancer treatments to be installed at IRE-IFO, the largest oncological hospital in Rome. It is the first proton therapy facility employing a full linear accelerator scheme based on high-frequency technology.

CHARACTERIZATION OF 27 MEV PROTON BEAM GENERATED BY TOP-IMPLART LINEAR ACCELERATOR

The first proton linear accelerator for tumor therapy based on an actively scanned beam up to the energy of 150 MeV, is under development and construction by ENEA-Frascati, ISS and IFO, under the Italian TOP-IMPLART project. Protons up to the energy of 7 MeV are generated by a customized commercial injector operating at 425 MHz; currently three accelerating modules allow proton delivery with energy up to 27 MeV. Beam homogeneity and reproducibility were studied using a 2D ionizing chamber, EBT3 films, a silicon diode, MOSFETs, LiF crystals and alanine dosimetry systems. Measurements were taken in air with the detectors at ~1 m from the beam line exit window. The maximum energy impinging on the detectors surface was 24.1 MeV, an energy suitable for radiobiological studies. Results showed beam reproducibility within 5% and homogeneity within 4%, on a circular surface of 16 mm in diameter.

PRELIMINARY STUDY OF NEUTRON FIELD IN TOP-IMPLART PROTON THERAPY BEAM

The TOP-IMPLART, a new proton therapy facility, is under development in Frascati ENEA Laboratories, near Rome. The project is centered on a medium-energy proton accelerator designed as a sequence of modular linear accelerators (the final energy will be 230 MeV). Being not a commercial product, measurements and simulation are fundamental to characterize the system and the radiation field, even during its construction. In this work some preliminary evaluations of the neutron contamination have been tried. The simulations were validated through some measurements obtaining a satisfactory agreement. A more detailed calculations and measurements campaign is scheduled for the next future.

Photoluminescent Color-Center Based Lithium Fluoride Radiation Detectors for Proton Beam Diagnostics

Lithium fluoride (LiF) is a well-known dosimeter material and is sensitive to any kind of ionizing radiation. A linear accelerator for protontherapy under development at ENEA C.R. Frascati was used to irradiate LiF crystals and thin films at room temperature with proton beams of 3 and 7 MeV energy in a dose range from 103 to 107 Gy. The irradiation of LiF induced the formation of stable F2 and F3+ color centers (CCs), which emit with broad photoluminescence (PL) bands under optical pumping at wavelengths close to 450 nm. By acquiring the PL image of the irradiated spots with a conventional fluorescence microscope, the transversal proton beam intensity was mapped with a high spatial resolution. The integrated PL intensity was also measured as a function of the irradiation dose: LiF films showed a linear PL response extending over three orders of magnitude of dose range, independently on the beam energy. It was also possible to measure the CCs PL distribution with proton penetration depth and direct imaging the Bragg peak, which gives an estimation of the proton beam energy. The sensitivity of the optical reading techniques and the high emission efficiency of CCs provided encouraging results to use photoluminescent color-center LiF-based radiation detectors for proton beam dosimetry and imaging applications.