NATURAL AND CVD TYPE DIAMOND DETECTORS AS DOSIMETERS IN HADROTHERAPY APPLI CATIONS Cirrone G.A.P., Cuttone G., Raffaele L., Sabini M.G., De Angelis C., Onori S., Pacilio M., Bucciolini M., Bruzzi M., Sciortino S. INFN-Laboratori Nazionali del Sud, Catania CATANA - Italian Center for Prothontherapy Istituto Superiore di Sanità, Roma Dipartimento di Fisiopatologia Clinica Università di Firenze, Firenze Dipartimento di Energetica, Università di Firenze, Firenze

Low dark current and low sensitivity to visible light Diamond is potentially a very suitable material for use as radiation dosimeter Wide band gap Low dark current and low sensitivity to visible light High carrier mobility Fast response Tissue equivalent No correction on the dose determination

Small dimensions and then high resolution High Radiation Hardness ....moreover High sensitivity Small dimensions and then high resolution Strong bonds High Radiation Hardness It is particularly indicated for measurements in regions of high radiation field gradient Proton beams... IMRT....IMPT

Our attention has been placed towards two different diamond detectors PTW NATURAL DIAMOND DE BEERS CVD DIAMOND FILM Irradiation with 62 AMeV proton beams from a superconducting cyclotron used for the treatment of ocular melanoma : CATANA facility Nominal current [nA] 4 Dose rate range [Gy/min] 2 - 15 Dose range [Gy] 2 - 20

PTW NATURAL DIAMOND Sensitive area: 4.3/4.5 mm2 Sensitive volume: 1.3/1.4 mm3 Thickness of sensitive volume: 0.30/0.31 mm Operating bias: 100 V In photon and electron beams the relative differences have been studied and already published (see De Angelis C et al. Med. Phys. 2002; 29(2): 248-254.) In proton beams the measured repeatability is 0.1%

Thickness of sensitive volume [mm] Sensitive surface [mm2] DE BEER CVD DIAMOND Thickness of sensitive volume [mm] 0,4 Sensitive volume [mm3] 6,4 16 Sensitive surface [mm2] Dark current [pA] 100 Operating bias [V] 400 Charge and current measurements from four electrodes Vsens is 1,6 mm3

Preirradiation Effects Relative dose distribution measurements For the characterization of each detector has been paid attention to: I – V characteristic Preirradiation Effects Dose linearity Relative dose distribution measurements Dose rate effects LET Dependence

DARK CURRENT AT 100 V CVD diamond 9 pA Specific resistance 2,7 * 1014  cm Natural diamond 2,5 pA Specific resistance 11,3 * 1014  cm SIGNAL TO NOISE RATIO AT 100 V CVD diamond 5000 Natural diamond 1000

I – V CHARACTERISTICS CVD Natural

CURRENT RESPONSE AND PREIRRADIATION (PUMPING EFFECTS) 3,5% after 15 Gy and 50 % increase 0,1 % after 15 Gy and 8 % fall off

CVD Natural DOSE LINEARITY Specific sensitivity 7,5 nC/CGy*mm3

DOSE RATE EFFECTS CVD Decrease: 4 % for natural 13 % for CVD

F Recombination time decreases with dose rate DOSE RATE EFFECTS Fower describes the dose rate linearity as Number of electron-hole pairs inside the material F From which Recombination time decreases with dose rate

DOSE RATE EFFECTS IF WE EXPRESS THE INDUCED CONDUCTIVITY AS  = 0.5 is expected for a pure material with no traps or for high excitation rate  = 1 for low excitation rate So for high recombination rate we expect  < 1 due to the lower recombination time

Fitting our experimental data with the semi-empirical formula: DOSE RATE EFFECTS Fitting our experimental data with the semi-empirical formula: 62 AMeV proton 6 MV Photon 62 AMeV proton 250 kV X-Ray

 =5,9 ns  =1 ns THE RECOMBINATION TIME RESULTS For the CVD diamond For the natural diamond  =1 ns And this justifies the higher sensitivity of CVD detector

DEPTH DOSE PROFILES ‘Pure’ Bragg peak SOBP

TRANSVERSAL PROFILES Lateral Penumbra 1mm 90/50 Ratio 0.89

LET and Dose-rate dependence (to investigate deeper) CONCLUSION Preirradiation LET and Dose-rate dependence (to investigate deeper) Good linearity with absorbed dose Good radiation hardness High sensitivity for the CVD LOW response time (rise time of 2 s)