2 nd ANNUAL ARDENT WORKSHOP Quality assessment of hadrontherapy
fields with TEPCs Paolo Colautti, INFN 2 nd Annual ARDENT Workshop,
Milano, 14-18 October 2013
Slide 2
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013 The
radiation quality concept The radiation field quality is meant as a
physical measurable quantity, which is significant for primary
effects on a biological system We define the measured y-spectrum in
1- 2 m sites as the radiation-field microdosimetric quality Some
detectors measure only, which is used as quality mark of the
radiation field. The couple of values and is a better quality mark
of the radiation field. RBE , the microdosimetric assessment of
RBE, can be an accurate quality mark for a given biological
end-point.
Slide 3
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Therapeutic beam constrains Fluence rates Proton continuos beam
BNCT facility 1 cm TEPC ought to measure at counting rates bigger
than 10 6 s -1 1 mm TEPC will measure at counting rates bigger than
10 4 s -1 CNAO protons per spill CNAO carbon ions per spill
Slide 4
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Energy calibration technique in ~ 1cm cylindrical TEPCs Vacuum tide
Al cylinder Tissue-equivalent conductive plastic
Slide 5
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Energy calibration technique in ~ 1mm cylindrical TEPCs -source Gas
IN Gas OUT Cathode H.V. Anode pulse Guard tubes H.V.
Slide 6
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Measurements at the Nice therapeutic proton beam
Slide 7
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Insulator surfaces damage without electric-field tubes 75 m
Slide 8
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Solution: a cavity inside the insulator to switch off the the
electronic avalanche 0.9 mm 0.150 mm 0.200 mm
Slide 9
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013 Mini
TEPC of 2.7 mm of external diameter
Slide 10
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Vacuum and gas flow apparatus Membrane pump Pressure readout
Exhaust Gas MFC MFC controller Turbo pump Solenoid valve
Slide 11
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Electronic chain HV anode HV cathode Pulser +18/-6 volt Low LET
amplifier Medium LET amplifier High LET amplifier Low LET MCA
Medium LET MCA High LET MCA
Slide 12
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Electronic chain
Slide 13
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Before measuring: linearity checks Integral linearity High LET
Slide 14
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Initial data from the 3 MCA
Slide 15
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013 Volt
calibration
Slide 16
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Logaritmic compaction 1 st 2 nd B th log y i log y i+1 1 st ..
Equal log intervals Example: B = 60 First decade y 1 = 1.0391, y 2
= 1.0798, y 3 . 1 = 0.04065 Second decade y 1 = 10.0391, y 2 =
10.0798, y 3 . 1 = 0.4065 Original counts Count density in
compacted intervals
Slide 17
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Sub-spectra junction Sub-spectra junction is not feasible if they
do not superimpose
Slide 18
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013 The
pulse-height frequency distribution
Slide 19
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013 The
pulse-height weighted distribution
Slide 20
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Lineal energy calibration ICRU 49 data 142 keV/m Calibration
factor: 142/475 = 0.299
Slide 21
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013 E
calculation in CSDA
Slide 22
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Maximum E-lost calculation in CSDA
Slide 23
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Lineal-energy dose distribution Fractional part of the visual area
is the fractional contribution to the the absorbed dose by the
corresponding y-events Blue points are used to linearly extrapolate
the frequency y- values down to 0.01 keV/m
Slide 24
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Weighting the dose distribution with a biological-significant
function Fractional part of the visual area is the fractional
contribution to the effective-dose of corresponding y- events The
weight is 1 for y-values < 10 keV/m The weight is 200 keV/m
Slide 25
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Splitting the dose spectrum in its neutron and gamma
components
Slide 26
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Quality of the conjunctive-melanoma proton-therapeutic beam
Slide 27
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013 The
therapeutic beam quality Iso dose map Iso effective-dose map Iso
RBE map
Slide 28
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013 Two
mini TEPCs for quality measurements of BNCT radiation fields
Slide 29
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013 The
twin TEPC for BNCT
Slide 30
30 BNCT dose components twin TEPC measurements
Slide 31
P.Colautti 2 nd ARDENT workshop. Milano 14-18 October 2013
Suggested lectures Glenn F.Knoll. Radiation Detection and
Measurements. John Wiley & Sons, NY, 1979 ICRU Report 36.
Microdosimetry. 1983
