1. 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

2. 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

3. 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

4. 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]
Dose range [Gy]

5. PTW NATURAL DIAMOND Sensitive area: 4.3/4.5 mm2
Sensitive volume: 1.3/ mm3
Thickness of sensitive volume: 0.30/0.31 mm
Operating bias: 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): )
In proton beams the measured repeatability is 0.1%

6. 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

7. 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

8. 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

9. I – V CHARACTERISTICS
CVD
Natural

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

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

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

13. 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

14. DOSE RATE EFFECTS
IF WE EXPRESS THE INDUCED CONDUCTIVITY AS
 = 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

15. 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

16.  =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

17. DEPTH DOSE PROFILES
‘Pure’ Bragg peak
SOBP

18. TRANSVERSAL PROFILES
Lateral Penumbra 1mm
90/50 Ratio 0.89

19. 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)