Detectors or small ield dosimetry Hugo Palmans MedAustron, Wiener Neustadt, Austria and National Physical Laboratory, Teddington, UK 1
080915 Overview Ideal detector Water calorimeter Ionization chamber Alanine Diodes, diamond, ilm, TLD, 2
Which detector to use? Read literature: IPEM report 103 Manuacturers manuals, e.g. PTW 3
IPEM report 103 4
Which detector to use? Read literature: IPEM report 103 Manuacturers manuals, e.g. PTW 5
Which detector to use? 6
Ideal detector Detector properties Stability Dose linearity Dose rate linearity Dose per pulse linearity Energy response Spatial resolution Size o detector Orientation Recommendation Short-term detector response should be better than 0.1% or a total combined dose o many hundreds o kgy rom multiple exposures. linearity better than 0.1% should be possible over a dose range o at least three orders o magnitude (e.g. 0.01 10 Gy) Linear accelerators are typically operated at dose rates o 100 Gy/s (instantaneous) and 0.01 Gy/s (averaged) and thereore detectors should be linear to better than 0.1% over this range. A detector s response with changing dose per pulse should remain stable to better than 0.1% ater correction or ion recombination. Essentially water equivalent The choice o suitable detector in terms o spatial resolution is usually based on a trade-o between adequately high signal-to-noise ratio and dosimeter size. The detector size should be such that the volume averaging correction is not larger than 5%. The response o a detector should ideally be independent o the orientation o the detector with 7
Calorimetry Radiation energy turns into heat heat is tiny, but measurable our primary standards or absorbed dose are calorimeters 8
0.5 mm Water calorimeter - thermistor probes (LSDG) 0.6 mm thermistor
Water calorimeter chemical heat deect D w = c w 1. D T. 1 - h 10
080915 Water calorimetry why does it not work or small ields Heath low: broad ield small ield 11
Problem: dose determination with ion chambers D D s p w = air w, air M W D = air m e air = M r V air W e OF = D D ield re = M ield M re ( s ( s w, air w, air ) ield ) re p p ield re correction actor 12
080915 1.00 0.80 Which one is right? M /M re 0.90 0.70 0.60 0.50 0.40 PTW 31002 (0.125cc) PTW 31016 (PinPoint) PTW 31003 (0.3cc) 0 20 40 60 80 100 square ield width / mm Krauss, Vienna, Feb. 2009, http://www.wienkav.at/kav/kj/91033454/physik/ptw/liquid.htm 13
Ion chambers or small ield dosimetry - Water to air stopping power ratios Eklund&Ahnesjö, PMB 53:4231 (2008) Andreo&Brahme PMB 8:839 (1986) 14
080915 Calibration in a 60 Co beam N D, w = D M w, 60 corr, Co 60 Co P 0 D w, 60 Co 15
080915 Dosimetry in a high-energy x-ray beam M corr, D w, (P 0 )=M corr, N D,w k Only B! 16
OF 080915 1.00 0.80 0.60 0.40 0.20 Dosimetry in a high-energy x-ray beam 0.00 0 20 40 60 80 100 square ield width / mm M corr, D w, (P 0 )=M corr, N D,w k Only B! 17
OF 080915 1.00 0.80 0.60 0.40 0.20 Dosimetry in a high-energy x-ray beam 0.00 0 20 40 60 80 100 square ield width / mm M corr, D w, (P 0 )=M corr, N D,w k Only B! 18
OF 080915 1.00 0.80 0.60 0.40 0.20 Dosimetry in a high-energy x-ray beam 0.00 0 20 40 60 80 100 square ield width / mm M corr, D w, (P 0 )=M corr, N D,w k Only B! 19
OF 080915 1.00 0.80 0.60 0.40 0.20 Dosimetry in a high-energy x-ray beam 0.00 0 20 40 60 80 100 square ield width / mm M corr, D w, (P 0 )=M corr, N D,w k Only B! 20
OF 080915 Plane-parallel chamber 1.00 0.80 0.60 0.40 0.20 0.00 0 20 40 60 80 100 square ield width / mm 21
OF 080915 Plane-parallel chamber 1.00 0.80 0.60 0.40 0.20 0.00 0 20 40 60 80 100 square ield width / mm 22
OF 080915 Plane-parallel chamber 1.00 0.80 0.60 0.40 0.20 0.00 0 20 40 60 80 100 square ield width / mm 23
Ion chambers: recombination 24 LeRoy et al., PMB 56:5637-51 (2011)
Ion chambers: polarity Agostinelli et al., Med Phys 35:3293-301 (2008) 25
080915 Which one is right? 1.00 0.90 0.80 M /M re 0.70 0.60 0.50 PTW 31002 (0.125cc) PTW 31016 (PinPoint) PTW 31003 (0.3cc) 0.40 0 20 40 60 80 100 Krauss, Vienna, Feb. 2009, square ield width / mm http://www.wienkav.at/kav/kj/91033454/physik/ptw/liquid.htm 26
080915 Which one is right? 1.00 0.90 0.80 M /M re 0.70 0.60 0.50 PTW 60012 (electron diode) PTW 60008 (photon diode) PTW 31018 (MicroLion) PTW 31002 (0.125cc) PTW 31016 (PinPoint) PTW 31003 (0.3cc) 0.40 0 20 40 60 80 100 Krauss, Vienna, Feb. 2009, square ield width / mm http://www.wienkav.at/kav/kj/91033454/physik/ptw/liquid.htm 27
080915 Which one is right? 1.20 1.00 M /M re 0.80 0.60 PTW 60012 (electron diode) PTW 60008 (photon diode) PTW 31018 (MicroLion) PTW 31002 (0.125cc) PTW 31016 (PinPoint) PTW 31003 (0.3cc) 0.40 0 20 40 60 80 100 square ield width / mm Krauss, Vienna, Feb. 2009, http://www.wienkav.at/kav/kj/91033454/physik/ptw/liquid.htm 28
Diodes or small ield dosimetry Sauer and Wilbert 2007 Med Phys 34:1983-8 29
Diamond detectors 1.20 (m en /r) carbon,water 1.00 0.80 0.60 0.40 0.20 volume averaging correction actor k vol Volume averaging correction actor (p vol ) 1.10 1.08 1.06 1.04 1.02 1.00 0.00 1E-03 10-3 1E-02 10-2 1E-01 10-1 1E+00 1 1E+01 10 0.98 0.96 photon energy / MeV 0 1 2 3 4 Side o square ield [cm] Diamond (diameter 2 mm) Diamond (diameter 3.2 mm) Diamond (diameter 4 mm) Diamond (4.3 x 4.3 mm 2 ) Diamond (5 x 3 mm 2 ) side o square ield / cm Lechner 2013 Radiother Oncol 109:356 30
Diodes and diamonds 31
Organic scintillators Cr. Louis Archambault 32
Liquid ionization chambers 33
Radiochromic ilm Ralston 2012 Phys Med Biol 57:2587 34
Alanine Amino acid / readout by ESR Pellets 2.5 mm thick and Ø 5 mm or 2.5 mm Water-equivalent Density 1.2 g cm -3 Bergstrand 2003 Phys Med Biol 48:1753 35
Real time detectors: diodes, diamond, Al2O3:C and scintillators Passive detectors Some others Table I. Summary o properties o detectors used in this study solid state detectors Detector type Dimensions o sensitive volume [mm] Material Z e Material density [g/cm 3 ] Electron density [e - /g] relative to water TLD chips 3.2 3.2 0.89 TLD-100 LiF:Mg,Ti 7.51 2.64 0.833 TLD µ-cubes 1 1 1 RPLD (GD-302M), Japan Length 6, diameter 1.5 TLD-100 LiF:Mg,Ti Silver activated phosphate glass 7.51 2.64 0.833 10.86 2.61 0.885 Alanine, NPL Thickness 2.3, diameter 5 Alanine/Parain 5.96 1.23 0.976 Alanine, DTU Thickness 2.8, diameter 4.8 Alanine/Parain 5.96 1.23 0.976 IBA SFD diode Thickness 0.06, diameter 0.6 Silicone 14 2.33 0.901 IBA PFD diode Thickness 0.06, diameter 2 Silicone 14 2.33 0.901 IBA EFD diode Thickness 0.06, diameter 2 Silicone 14 2.33 0.901 PTW 60003 diamond Thickness 0.1-0.4 Sensitive area 3-15.2 Diamond 6 approximately 3.5 0.901 Al 2 O 3 :C, DTU 0.5 0.5 2 Al 2 O 3 :C 10.60 3.97 0.883 Saint Gobain BCF-60 scintillator 1 Length 1, diameter 1 Polystyrene 5.70 1.06 0.975 Saint Gobain BCF-60 scintillator 2 Length 2, diameter 0.5 Polystyrene 5.70 1.06 0.975 36 the density varies depending on the purity o the diamond used
Field output actors correction actors / components Scott et al. 2012 Phys. Med. Biol. 57:4461 37
Other proposals to actorize SF correction actors Bouchard et al. 2009 Med. Phys. 36:4654 Crop et al. 2009 Phys. Med. Biol. 54:2951 Czarnecki and Zink 2013 Phys. Med. Biol. 58:2431 Fenwick et al. 2013: Phys. Med. Biol. 58:2901 38
Correction actors or unshielded diodes Francescon et al 2011, Med Phys 38:6513 Benmakhlou et al 2014, Med Phys 41:041711 39
Ch 5 Practical implementation dosimetry / availability, re data k, re 40
Ch 6 Practical implementation relative dosimetry / correction actors or OF e.g. CyberKnie / iris collimator E 0 =7.0 MeV, FWHM spot 2.1 mm Field size / mm 5 7.5 10 12.5 15 20 25 PTW 60008 0.947 0.964 0.976 0.987 0.991 0.998 1.005 PTW 60012 0.964 0.975 0.979 0.992 0.996 0.999 1.002 PTW 60017 0.960 0.971 0.981 0.991 0.996 0.999 1.002 PTW 60018 0.954 0.966 0.978 0.988 0.994 0.998 1.002 SN Edge 0.947 0.959 0.973 0.980 0.986 0.993 1.000 Exradin A16 1.095 1.039 1.009 1.006 1.003 1.004 1.005 PTW 31014 1.102 1.044 1.010 1.006 1.003 1.001 0.999 PTW microlion 1.027 1.001 0.997 0.993 0.996 0.998 0.999 Francescon et al. 2012 Med Phys 57:3741 k,, re re 41
, 080915 Field output actors Monte Carlo calculated correction actors CyberKnie Dierent FWHM primary source k, k k,,,, = = a M M,, b,, = 60 mm collimator,, Francescon et al 2008 Med Phys 35:504-13 42
43 Field output actors: 080915 (1) (2) (2) (2) (1) (1) (2) (1),,,,,, rel rel M M M M M M k k = = w w w w k M M M D M D M M D D,,,,,,,, = = = w w M M D D k =,,,,
080915 Field output actors - CyberKnie:,, ( 1 ) ratio o correction actors (MC or vol),, ( 6 Point ode 60008 ode 60012 GE nine D T ilm lymer gel k 2 ) Pantelis et al. 2010 Med Phys 37:2369 M / M60 k 1.050 1.000 0.950 0.900 0.850 0.800 0.750 0.700 0.650 0.600 1.15 1.10 1.05 1.00 0.95 0.90 0.85 A16 PinPoint Diode 60008 Diode 60012 EDGE Alanine TLD EBT ilm Polymer gel M / Mre 0.75 0.70 0.65 0 5 10 15 20 0.60 0.55 0.50 diameter / mm Diode 60008 Diode 60012 EDGE (M/M 60 ) 2 /(M/M 60 ) 1 1.300 1.250 1.200 1.150 1.100 1.050 1.000 0.950 0 5 10 15 20 1.300 1.250 1.200 1.150 1.000 diameter / mm TLD 1.100 ExrA16 PinPoint EBT ilm SHD USD EDGE alanine TLD EBT GEL Polymer gel 1.050 detector PinPoint Diode 60008 Diode 60012 EDGE Alanine TLD EBT ilm Polymer gel 0.950 0 5 10 15 20 diameter / mm ( M / M re ) * k, PinPoint Diode 60008 Diode 60012 EDGE Alanine 44
Field output actors correction actors PTW-60012 IBA SFD 45
Field output actors correction actors PTW-60008 PTW-31006 PTW-31002 46
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