RIVELATORI A STATO SOLIDO BASATI SU FOTOLUMINESCENZA DI

RIVELATORI A STATO SOLIDO BASATI SU FOTOLUMINESCENZA DI DIFETTI IN CRISTALLI E FILM DI FLUORURO DI LITIO CARATTERIZZAZIONE DI FASCI DI PROTONI (3 - 7 Me. V) DOSIMETRIA (PROTONI, RAGGI X, Co 60) Massimo Piccinini Francesca Bonfigli Rosa Maria Montereali Stefano Libera Maria Aurora Vincenti ENEA C. R. Frascati, UTAPRAD-MNF Jose Eduardo Villarreal-Barajas ENEA guest Department of Oncology University of Calgary Tom Baker Cancer Centre, Calgary AB, Canada 1

Motivation Lithium Fluoride, Li. F : well known thermoluminescent dosimeter (TLD) material Tissue equivalent Radiation sensitive (gamma, X-rays, electrons, ions. . . ) Optically Stimulated Luminescence (OSL): versatile reading technique for novel dosimetric materials (i. e. Al 2 O 3: C) in clinical dosimetry Fast reading High sensitivity Dose imaging Solid-state X-ray imaging detectors based on photoluminescence (PL) of color centers in Li. F crystals and thin films proposed, tested and under development at ENEA C. R. Frascati (ENEA patent 2002, ENEA patent 2013) PECULIARITIES: high spatial resolution ( intrinsic < 2 nm, standard < 250 nm ) large field of view ( > 1 cm 2 ) wide dynamic range ( > 103) efficient optical readout process (optical fluorescence microscopy) easy handling: no development needs and no sensitivity to visible light R&D of solid-state Li. F based detectors for proton beam imaging and dosimetry in the framework of TOP-IMPLART project 2

Colored Li. F crystals containing color centers induced by gamma rays irradiation. Li. F crystal containing colored areas realized by low energy electron beams. (Courtesy of Dr. V. Kalinov, Minsk, Belarus). 3

Colored Li. F films Li. F film thermally evaporated on a silicon substrate at the Solid State Lab. (UTAPRAD-MNF) Soft X-ray radiography of a dragonfly wing on a Li. F film on silicon (irradiation performed in a laserplasma source at UTAPRAD-SOR). Soft X-ray radiography of macrophagies on a Li. F crystal (irradiation performed in a laser-plasma source at University Tor Vergata). 4

Li. F-based detector for proton beam imaging Step 1 Exposure of Li. F crystal or film to proton beam H+ beam Li. F detector Step 2 Optical reading of color centers photoluminescence signal by a conventional fluorescence microscope Photoluminescence of F 2, F 3+ CCs (535 -670 nm) Pump light (458 -488 nm) Irradiated Li. F detector Li. F crystal Li. F thin film detector

Proton beam irradiation of Li. F crystals and thin films Proton Beam parameters Li. F samples Energy: 3 Me. V and 7 Me. V (pulsed source @ 50 Hz) • Polished Li. F crystals: 10 x 1 mm 3 Actual Energy after 50 mm thick kapton window: 2. 23 Me. V and 6. 65 Me. V • 1 mm thick polycristalline Li. F films thermally evaporated on glass substrates Pulse duration: 60 ms Charge/pulse: 58 p. C SRIM simulation Beam diameter: ~ 3 mm Fluence range: protons/cm 2 1010 – 1015 Proton implantation depth in Li. F @ 2. 23 Me. V: 45 mm Proton implantation depth in Li. F @ 6. 65 Me. V: 295 mm SRIM software: The Stopping and Range of Ions in Matter J. F. Ziegler, M. D. Ziegler, J. P. Biersack; Nucl. Instrum. Methods B 268 (2010) 1818 6

Proton beam images on Li. F crystals 7 Me. V beam 3 Me. V beam 7

Proton beam images on Li. F crystals vs Li. F films Li. F crystal Li. F film

Proton beam images on Li. F crystals

Proton beam images on Li. F crystals

Photoluminescence Spectra of proton irradiated Li. F crystals vs Li. F thin films PL spectra of irradiated areas on Li. F crystals and films were measured at RT by pumping in a continuous regime with the 458 nm line of an Argon laser. It allows to simultaneously excite the green and red emissions of F 3+ and F 2 centers, respectively. The PL signal was spectrally filtered by a monochromator and acquired by means of a photomultiplier with lock-in technique. 3 Me. V Proton beam F 2 F 3+ band peaked at 535 nm F 2 band peaked at 670 nm SRIM simulation

Photoluminescence Intensity vs Dose of 3 Me. V irradiated Li. F crystals and thin films PL spectra were deconvolved into the sum of two Gaussian bands ascribed to the emission bands of the F 2 and F 3+ centers, in order to separate their contribution to the total PL intensity and to check the PL linear behaviour range with the dose. Crystals: average dose Films: actual dose 3 Me. V Proton beam For both Li. F crystals and thin films the PL linear behaviour covers several orders of magnitude of dose range, but it is extended towards higher dose values in films, because in the portion of the crystal around the Bragg peak was released a dose 3. 5 times higher than that released in the film.

Photoluminescence (image) intensity vs Dose measured by the fluorescence microscope When acquiring the image of an irradiated spot with the fluorescence microscope, the camera exposure time must be set accurately in order to exploit the whole available gray scale, so the image histogram must be spread as much as possible along the horizontal axis. After acquiring the images of all the spots, the “integrated density” of each image was calculated by Image. J software, and normalized to the exposure time of 1 second. It corresponds to the total spectral intensity measured at the optical bench. 3 Me. V A good data agreement with laser excitation and lock-in techniques was obtained. M. Piccinini F. Ambrosini, A. Ampollini, M. Carpanese, L. Picardi, C. Ronsivalle, F. Bonfigli, S. Libera, M. A. Vincenti and R. M. Montereali. ; Nucl. Instrum. Methods B (2014) in press

Fluorescence microscope images: noise subtraction for 3 and 7 Me. V proton irradiated Li. F crystals and films At low doses in Li. F films the background noise gets higher because long exposure times are required (deviation from linearity). Using the fluorescence microscope it is possible to substract from the images the background noise, pushing the microscope camera to its real limit. The background noise is calculated by reading the image density of an area outside the luminescent spot.

PL Intensity vs Dose of 3 Me. V and 7 Me. V irradiated Li. F crystals and thin films • In Li. F crystals the PL intensity is proportional to the total beam energy released into the crystal (average dose). • In Li. F films the PL intensity is not dependent on the beam energy, but only on the actual dose released into the 1 mm thick film. Linearity range (Li. F films): 103 – 106 Gy

Dosimetry on Li. F crystals (X-Rays, at low doses (0. 5 -100 Gy) 60 Co) Sample irradiated at Tom Baker Cancer Center in Calgary on 11/12/2013 Seven Li. F crystals, dimensions 5 x 5 x 0. 5 mm 3, irradiated with a 6 Me. V X-ray radiotherapy source, placed in a “solid water” phantom to get equilibrium conditions and a uniform dose distribution within the whole crystal volume. The following equvalent doses to water were given: 1, 10, 20, 50, 100 Gy. Two samples at 100 Gy were irradiated to test reproducibility and also a sample at an unknown dose to test the calibration. Samples irradiated at INMRI Casaccia on 22/01/2014 Five Li. F crystals, dimensions 5 x 5 x 0. 5 mm 3, irradiated with 60 Co source, placed in a PMMA phantom. The following equvalent doses to water were given: 1, 10, 20, 50, 70 Gy. Samples irradiated at the hospital of Terni on 24/01/2014 Seven Li. F crystals, dimensions 5 x 5 x 0. 5 mm 3, irradiated with a 5 Me. V X-ray radiotherapy source, placed in a PMMA phantom. The following equvalent doses to water were given: 0. 5, 1, 5, 10, 20 Gy.

Fluorescence image acquisition and PL signal reading Images taken placing each crystal next to an unirradiated one and viewing the contact border; this way half of the field of view is occupied by the irradiated sample and the other half by the unirradiated one. In each image two 150 x 150 pixel (0. 975 x 0. 975 mm 2) were selected, one within the irradiated crystal and the other one within the unirradiated one. The area centers are at the same distance from the contact border (at about 250 pixel=1. 625 mm). The signal intensity of both areas is measured by the “Integrated density” function of Image. J software and then normalized to the exposure time of 1 second.

Calibration curve: Reproducibility of PL reading Calibration curves obtained independently in two different days (1 st and 2 nd calibration) on Li. F crystals (6 Me. V X-ray radiotherapy source) • Linearity with dose • Good (5%) reproducibility of PL reading

PL calibration curve: Co 60 vs 6 Me. V X-Rays Calibration curves on Li. F crystals • Linearity with dose • Very good (2%) agreement between points corresponding to same doses of the two selected sources

PL calibration curve: Co 60 vs 5 and 6 Me. V X-Rays Very good (2%) agreement between points corresponding to same doses of the three selected sources at low doses (0. 5 – 20 Gy).

Color centers PL linear response at low doses The total PL behavior is linear with dose. The PL behavior of F 2 centers is super-linear, while the one of the F 3+ centers is sub-linear, but their deviation from linearity is perfectly compensated so that their sum results to be linear.

The Bragg peak SRIM simulation PL to the microscope Li. F sample Proton beam Irradiation geometry The concentration of color centers along the protons path is proportional to the energy lost by the protons, so a maximum of luminescence intensity should be located at the Bragg peak position.

The Bragg peak: 3 Me. V protons Li. F film on silicon Bragg peak 100 mm 3 Me. V Proton beam Li. F film border 3 Me. V Proton beam A 1 mm thick Li. F film thermally evaporated on a silicon substrate was cut into two pieces. One of the pieces was exposed to the proton beam, with the film border towards the beam and the film plane parallel to the beam propagation direction.

The Bragg peak: 3 Me. V protons on Li. F film • A part of the image with a straight film border is selected. • The image intensity profile is calculated for each pixel-line perpendicular to the film border. • The intensity profiles are averaged to improve the signal-tonoise ratio. • The pixel distance between the peak intensity and the film border (slope) is calculated and converted into the corresponding length after the image scale is known, providing the Bragg peak position. Energy: 3 Me. V Image scale: 0. 4 mm/pixel Bragg peak (SRIM simulation): 23. 5 ± 4 mm Bragg peak (by imaging): 19. 5 ± 0. 8 mm (preliminary results)

The Bragg peak: 7 Me. V protons on Li. F film border PL to the microscope Li. F film Li. F sample Proton beam 7 Me. V Proton beam 100 mm Energy: 7 Me. V Image scale: 1. 96 mm/pixel Selected area

The Bragg peak: 7 Me. V protons on a Li. F crystal border PL to the microscope Li. F crystal Li. F sample Proton beam 7 Me. V Proton beam Energy: 7 Me. V Image scale: 1. 96 mm/pixel Selected area

The Bragg peak: 7 Me. V protons Preliminary results SRIM simulation: 274 ± 2 mm Li. F crystal: 263 ± 2 mm Li. F film: 253 ± 2 mm

Future work • Irradiations with high energy protons (100 -250 Me. V) and Carbon ions (100 -450 Me. V/u) at CNAO • Increasing the PL signal sensitivity at low doses for Li. F crystals and thin films • Comparison of Li. F-based detectors/dosimeters with other ones (i. e. EBT-3, HDV-2) • Experiments focused on the Bragg peak THANK YOU FOR YOUR ATTENTION