CARATTERIZZAZIONE DI FASCI DI PROTONI (3 - 7 MeV) RIVELATORI A STATO SOLIDO BASATI SU FOTOLUMINESCENZA DI DIFETTI IN CRISTALLI E FILM DI FLUORURO DI LITIO CARATTERIZZAZIONE DI FASCI DI PROTONI (3 - 7 MeV) DOSIMETRIA (PROTONI, RAGGI X, Co60) 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

Radiation sensitive (gamma, X-rays, electrons, ions...) Motivation Lithium Fluoride, LiF : 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. Al2O3:C) in clinical dosimetry Fast reading High sensitivity Dose imaging Solid-state X-ray imaging detectors based on photoluminescence (PL) of color centers in LiF 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 cm2 )  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 LiF based detectors for proton beam imaging and dosimetry in the framework of TOP-IMPLART project 2

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

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

LiF-based detector for proton beam imaging Step 1 Exposure of LiF crystal or film to proton beam Step 2 Optical reading of color centers photoluminescence signal by a conventional fluorescence microscope H+ beam LiF detector LiF thin film detector LiF crystal Irradiated LiF detector Pump light (458-488 nm) Photoluminescence of F2, F3+ CCs (535-670 nm) 5

Proton beam irradiation of LiF crystals and thin films Proton Beam parameters Energy: 3 MeV and 7 MeV (pulsed source @ 50 Hz) Actual Energy after 50 mm thick kapton window: 2.23 MeV and 6.65 MeV Pulse duration: 60 ms Charge/pulse: 58 pC Beam diameter: ~ 3 mm Fluence range: 1010 – 1015 protons/cm2 Proton implantation depth in LiF @ 2.23 MeV: 45 mm Proton implantation depth in LiF @ 6.65 MeV: 295 mm LiF samples Polished LiF crystals: 10x10x1 mm3 1 mm thick polycristalline LiF films thermally evaporated on glass substrates SRIM simulation 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

Proton beam images on LiF crystals 7 MeV beam 3 MeV beam 3 MeV beam 7 MeV beam 7

Proton beam images on LiF crystals vs LiF films 8

Proton beam images on LiF crystals 9

Proton beam images on LiF crystals 10

F2 F3+ Photoluminescence Spectra of proton irradiated LiF crystals vs LiF thin films PL spectra of irradiated areas on LiF 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 F3+ and F2 centers, respectively. The PL signal was spectrally filtered by a monochromator and acquired by means of a photomultiplier with lock-in technique. F2 F3+ 3 MeV Proton beam F3+ band peaked at 535 nm F2 band peaked at 670 nm SRIM simulation

Crystals: average dose Photoluminescence Intensity vs Dose of 3 MeV irradiated LiF crystals and thin films PL spectra were deconvolved into the sum of two Gaussian bands ascribed to the emission bands of the F2 and F3+ 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 MeV Proton beam For both LiF 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 ImageJ software, and normalized to the exposure time of 1 second. It corresponds to the total spectral intensity measured at the optical bench. 3 MeV 3 MeV 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 MeV proton irradiated LiF crystals and films At low doses in LiF 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.

Linearity range (LiF films): 103 – 106 Gy PL Intensity vs Dose of 3 MeV and 7 MeV irradiated LiF crystals and thin films In LiF crystals the PL intensity is proportional to the total beam energy released into the crystal (average dose). In LiF 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 (LiF films): 103 – 106 Gy

Dosimetry on LiF crystals (X-Rays, 60Co) at low doses (0.5-100 Gy) Sample irradiated at Tom Baker Cancer Center in Calgary on 11/12/2013 Seven LiF crystals, dimensions 5x5x0.5 mm3, irradiated with a 6 MeV 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 LiF crystals, dimensions 5x5x0.5 mm3, irradiated with 60Co 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 LiF crystals, dimensions 5x5x0.5 mm3, irradiated with a 5 MeV 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 150x150 pixel (0.975x0.975 mm2) 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 ImageJ 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 (1st and 2nd calibration) on LiF crystals (6 MeV X-ray radiotherapy source) Linearity with dose Good (5%) reproducibility of PL reading

PL calibration curve: Co60 vs 6 MeV X-Rays Calibration curves on LiF crystals Linearity with dose Very good (2%) agreement between points corresponding to same doses of the two selected sources

PL calibration curve: Co60 vs 5 and 6 MeV 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 F2 centers is super-linear, while the one of the F3+ 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 Proton beam LiF sample 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 MeV protons LiF film on silicon Bragg peak 3 MeV Proton beam 3 MeV Proton beam 100 mm LiF film border A 1 mm thick LiF 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 MeV protons on LiF 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-to-noise 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 MeV 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 MeV protons on LiF film LiF film border PL to the microscope Proton beam LiF sample LiF film 7 MeV Proton beam 100 mm Selected area Energy: 7 MeV Image scale: 1.96 mm/pixel

The Bragg peak: 7 MeV protons on a LiF crystal LiF crystal border PL to the microscope Proton beam LiF sample LiF crystal 7 MeV Proton beam Selected area Energy: 7 MeV Image scale: 1.96 mm/pixel

The Bragg peak: 7 MeV protons Preliminary results SRIM simulation: 274 ± 2 mm LiF crystal: 263 ± 2 mm LiF film: 253 ± 2 mm

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