NPL s rogress towards absorbed dose standards for roton beams H. Palmans 1 R. Thomas 1 D. Shiley 1 A. Kacerek 2 1 National Physical Laboratory Teddington United Kingdom 2 Clatterbridge Centre of Oncology Wirral United Kingdom hugo.almans@nl.co.uk Presented at the Worksho on Absorbed Dose and Air Kerma Standards Paris 9-11 May 2007
Overview Proton theray and to a lesser extent ion theray are treatment modalities of increasing imortance Dosimetry has not been as well established as in highenergy x-ray beams NPL s activities in imroving roton and ion dosimetry: SR roject 2002-2004 Grahite calorimetry Interaction data Alanine dosimetry Monte Carlo simulation of erturbation correction factors
Toics discussed in this talk Calorimetry - Grahite calorimetry in CCO beam - Develoment of a rimary standard level grahite calorimeter for lightions Interaction/basic data -(w ) value - Stoing owers - Non-elastic nuclear interaction cross sections Correction factors for ionization chambers related to: - Recombination - Dose gradients - Secondary electrons - Non-elastic nuclear interactions
Why rotons?
Grahite calorimetry for rotons CCO (Palmans et al 2004 Phys Med Biol 49:3737-49) 30 mm 27.406 27.404 T (ºC) 27.402 27.400 27.398 27.396 0 500 1000 1500 2000 2500 3000 3500 4000 4500 time (s)
Grahite calorimetry for rotons CCO (Palmans et al 2004 Phys Med Biol 49:3737-49) Heat transfer: FE (Comsol) Volume/ga effects: MC (McPTRAN.RZ) 1.050 1.005 Δ T (K) 0.0170 0.0150 0.0130 0.0110 0.0090 0.0070 0.0050 0.0030 measurement 0.0010 simulation -0.0010 100.0 150.0 200.0 250.0 300.0 350.0 400.0 t (s) k volunmodulated 1.030 1.010 0.990 0.970 1.004 1.003 1.002 1.001 1.000 0.999 0.998 0.997 0.996 0.950 0.995 0.0 0.5 1.0 1.5 2.0 2.5 deth (cm grahite) k volmodulated
Grahite to water conversion 1: interaction cross sections (ICRU-49 and ICRU-63) 1.15 (a) 1.00 (b) 1.14 0.95 s wg 1.13 1.12 [σnucl/a] wg 0.90 0.85 1.11 0.80 1.10 1.E+00 1.E+01 1.E+02 1.E+03 Energy (MeV) 0.75 0 100 200 300 Energy (MeV)
Grahite to water conversion 2: dose conversion (ICRU-49 and ICRU-63) D w = D g x conversion 1.025 1.020 1.015 1.010 1.005 1.000 0.995 0.990 stoing ower ratio only stoing ower ratio and nuclear interactions 1% 0.5% 0.985 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Water equivalent deth (cm)
Grahite to water conversion 3: fluence correction Fluence correction factor 1.050 1.040 1.030 1.020 1.010 1.000 GEANT4 MCNPX McPTRAN.MEDIA Exeriment in hantom (relimin) Exeriment FC (relimin) 0.990 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Water equivalent deth (cm)
Grahite calorimetry results CCO 1.02 modulated beam non-modulated beam 1.04 Jun-03 1.01 Jun-03 1.03 Jun-03 1.00 Jun-03 1.02 Dcal/Dion 0.99 Jun-03 1.01 0.98 Jun-03 1.00 NE2561 (Co-60) 0.97 NACP02 (Co-60) Markus (Co-60) NACP02 (e-19) Jun-03 0.99 0.96 Markus (e-19) 0.98
Uncertainty
New standard level grahite calorimeter for light-ion beams (cfr Mark Bailey / this worksho) Either calibrate ionization chambers or measure k Q data Large enough for scatter build-u Light enough to be ortable Robustness vacuum oeration core size erturbation alignment and beam monitoring considerations
Derivation of (w ) from calorimeter measurements c c w c w s W s w ) ( ) ( ) ( ) ( c D w cal w c D w D w Q N M D N N k = = w c D w c c w c cal w s N s W D w = ) ( ) ( ) ( ) ( M
Imortance: new recommendation on roton dosimetry by ICRU/IAEA 370 New ICRU/IAEA Jones 2006 (Rad Phys Chem 75:541-50) 360 (w ) (J/C) 350 340 IAEA TRS398 New ICRU/IAEA Medin et al 2006 (Phys Med Biol 51:1503-21) 330 0 100 200 300 400 E (MeV)
Faraday cu measurements for range and attenuation measurements Proton beam Monitor chamber 9.0 Plates Faraday cu Guard 8.0 Charge (nc) 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 Measured data oints Attenuation fit Tangent at 50% range Distal edge fit To electrometer 0.0 1.0 2.0 3.0 4.0 Grahite thickness (cm)
Range results
Nuclear attenuation results Factor 2 to 3 higher than exected from ICRU 63 tables: not as yet understood. Hyothesis: wide angle secondary rotons: Faraday cu Plates Guard
Correction factors for ionization chambers: recombination (Palmans et al 2006 Phys Med Biol 51:903-17) BEAM IC1 IC2 PHANTOM Dose rate (Gy s -1 ) 0.4 0.3 0.2 z = 23 mm z = 20 mm z = 10 mm surface 0.1 IC AIR CAVITIES 0.0 0.0 0.2 0.4 0.6 0.8 1.0 Time (in 1/8 revolutions) 1.080 1.070 1.060 (d) 1.018 1.016 1.014 1.012 1.010 1.050 ion 1.008 I V /I V/n 1.040 1.030 1.006 1.004 1.002 1.020 1.000 1.010 1.000 0.0 1.0 2.0 3.0 I V or I Veff (na) 0.998 Equation (1) Pulsed (Boag) Markus 1 Markus 2
Perturbation correction factors for ionization chambers rotons Dwater = D S ρ SA water cav wall cel dis For high-energy x-rays: tyical corrections of level 1% alied since 1970 s For rotons: not alied in any recommendation
dis : Monte Carlo - McPTRAN.CAVITY (Palmans 2006 Phys Med Biol 51:3483-501) Proton beam dϕ /de E Secondary electrons: 2 3 Geometry interrogation region EGSnrc + variance reduction techniques (Verhaegen&Palmans 2001 Med. Phys. 28:2088) 1 D in cavities ~~~~~~~~~~~~~~~~~ Histories resumed Chamber comlete New deth ~~~~~~~~~~~~~~~~~ Variance reduction Lateral range rejection History slitting ~~~~~~~~~~~~~~~~~ PDD IC comared with PDD in homogeneous water
dis : analytical model Integrating the deth dose curve (Palmans 2006 Phys Med Biol 51:3483-501) x R sleeve R wa Rll ca v R c el Proton I water O PQ S T U sleeve wall c.e. z z 0
dis : comarison with exeriment PDD s (Palmans 2006 Phys Med Biol 51:3483-501) Mobit et al. 2000 Med. Phys. 27:2780-2787 78 MeV rotons Jäkel et al. 2000 Phys. Med. Biol. 45:599-607 3 GeV 12 C 2.5 4.5 4.0 normalised dose (a.u.) 2.0 1.5 1.0 0.5 Attix Caintec PR06 Reconstructed relative dose 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Reference PTW-30006 Markus Reconstructed 0.0 0.0 0.0 20.0 40.0 60.0 115.0 120.0 125.0 130.0 deth (mm) deth (mm)
cave : SA cavity theory due to secondary electrons rotons δ-electrons D med = = D S ρ SA med med S D cave ρ cav e = S ρ SA med S ρ med
walle : SA cavity theory rotons δ-electrons D med = D S ρ SA med wall S ρ med wall = med SA S D walle ρ = walle S ρ med wall SA S ρ wall SA S ρ med
cave & walle : SA cavity theory for FWT-IC18 tye chamber 1.010 FWT-IC18 1.008 cave.walle 1.006 1.004 1.002 1.000 PCAV*PWALL_P_TEP_E_TEE 50 MeV 150 MeV 250 MeV 0.998 0.01 0.10 1.00 10.00 100.00 R res
cave & walle : Monte Carlo versus SA cavity theory (sher r = 0.25cm Δ = 13.2 kev) cave.walle 1.010 1.008 1.006 1.004 A150 C PMMA water 1.002 1.000 0 50 100 150 200 250 300 E eff (MeV)
Chamber # cave & walle : comarison with exeriment 1.020 Nylon66-Al 1.015 PMMA-Al &PTW30001 ExrT2 D wne2571 /D wch 1.010 1.005 C-C &PTW30002 A150-Al &NE2581 IC18 1.000 0.995 0 5 10 15
walln : (simlistic) analytical model for slowing down sectra secondary & α (NE2571 150 MeV) due to secondaries from nonelastic nuclear interactions : α: water bulk 5.0E-04 1.0E-05 4.0E-04 8.0E-06 φ E ( cm-2mev-1) 3.0E-04 2.0E-04 φ E ( cm-2mev-1) 6.0E-06 4.0E-06 1.0E-04 2.0E-06 0.0E+00 0 20 40 60 80 100 120 140 E (MeV) 0.0E+00 water wall grahite wall 0 20 40 60 80 100 120 140 E (MeV)
walln : secondary & α erturbation (NE2571) erturbation factor 1.002 1.000 0.998 0.996 0.994 0.992 +α 0 50 100 150 200 250 300 E (MeV) BUT: ICRU 63 data (u C ~ 30-40%) Crude model MC study needed
Summary Grahite calorimetry Many oeration characteristics erturbation factors and heat transfer henomena are similar as for hotons Primary standard level calorimeter is being built Conversion to dose to water is a serious issue Interaction/basic data: Substantial contribution to (w ) value Range and attenuation measurements Ionization chambers Corrections for recombination gradients and secondary electrons Further work: non-elastic nuclear interactions
Acknowledgments Simon Duane Thomas Russell David Shiley Mark Bailey Alan DuSautoy Andrzej Kacerek (CCO) Frank Verhaegen Jan Seuntjens and