Processing of Imaging Data H=1000μtsue/μwater SP=dE/dxtissue/dE/dxwater CT Relative Hounsfield proton values (H) stopping Calibration power (SP) curve Dose calculation Isodose distribution
Processing of Imaging Data CT Hounsfield values (H) Isodose distribution Calibration curve H = 1000 m tissue /m water Relative proton stopping power (SP) SP = dE/dxtissue /dE/dxwater H SP Dose calculation
CT Calibration Curve ·Proton interaction≠Photon interaction Bi-or tri-or multisegmental curves are in use No unique SP values for soft tissue Hounsfield range ·Tissue substitutes≠real tissues ·Fat anomaly
• Proton interaction Photon interaction • Bi- or tri- or multisegmental curves are in use • No unique SP values for soft tissue Hounsfield range • Tissue substitutes real tissues • Fat anomaly CT Calibration Curve
CT Calibration Curve Stoichiometric Method* 2000 Step 1:Parameterization of H 1800 Choose tissue substitutes 1600 Obtain best-fitting parameters A, B,C 1400 1200 H=Ne"el A (ZPE)3.6+B (Zeoh)1.9 +C 1000 800 Rel. Photo Coherent 800100012001400160018002000 electron Klein- electric Hounsfield value (expected) density scattering effect Nishina cross section *Schneider U.(1996),"The calibraion ofCT Hounsfield units for radiotherapy treatment planning," Phys.Med.Biol.47,487
CT Calibration Curve Stoichiometric Method* • Step 1: Parameterization of H – Choose tissue substitutes – Obtain best-fitting parameters A, B, C 800 1000 1200 1400 1600 1800 2000 800 1000 1200 1400 1600 1800 2000 Hounsfield value (expected) Hounsfield value (observed H = Ne rel {A (ZPE) 3.6 + B (Zcoh) 1.9 + C} KleinNishina cross section Rel. electron density Photo electric effect Coherent scattering *Schneider U. (1996), “The calibraion of CT Hounsfield units for radiotherapy treatment planning,” Phys. Med. Biol. 47, 487
CT Calibration Curve Stoichiometric Method .8 Step 2:Define Calibration Curve 1.6 select different standard tissues 1.4 with known composition (e.g., 1.2 Fat ICRP) calculate H using parametric 0.8 equation for each tissue 0.6 calculate SP using Bethe Bloch 0.4 equation 0.2 fit linear segments through data 500 1000 15002000 2500 points H value
CT Calibration Curve Stoichiometric Method 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 0 500 1000 1500 2000 2500 H value SP • Step 2: Define Calibration Curve – select different standard tissues with known composition (e.g., ICRP) – calculate H using parametric equation for each tissue – calculate SP using Bethe Bloch equation – fit linear segments through data points Fat
CT Range Uncertainties Two types of uncertainties inaccurate model parameters beam hardening artifacts Expected range errors mm 4 mm Soft tissue Bone Total H2O range abs.error H,O range abs.Error abs.error (cm) (mm) (cm) mm】 (mm) Brain 10.3 1.1 1.8 0.3 1.4 Pelvis 15.5 1.7 9 1.6 33
CT Range Uncertainties • Two types of uncertainties – inaccurate model parameters – beam hardening artifacts • Expected range errors Soft tissue Bone Total H2O range abs. error H2O range abs. Error abs. error (cm) (mm) (cm) (mm) (mm) Brain 10.3 1.1 1.8 0.3 1.4 Pelvis 15.5 1.7 9 1.6 3.3 1 mm 4 mm