DUAL-ENERGY CT IN PROTON THERAPY

Transcription

1 10/31/17 DUAL-ENERGY CT IN PROTON THERAPY Isabel Almeida, MAASTRO Clinic 7th NCS Lustrum Symposium 1

2 10/31/ Range uncertainties and margins Margin recipes Example: 3.5%*R +1mm *Figures from PhD Thesis of Verburg JM, Reducing Range Uncertainty in Proton Therapy 30 cm range -> 1.15 cm margin More on range uncertainties: Paganetti H. Phys Med Biol Jun 7; 57(11): R99 R117 2

3 Contents Dual-energy CT (DECT) DECT in proton therapy (PT) Uncertainties in DECT for PT Final remarks DUAL ENERGY COMPUTED TOMOGRAPHY (DECT) 3

4 SINGLE-SOURCE DECT DUAL-SOURCE DECT Single-source DECT DUAL-SPIRAL TWIN-BEAM 1 st scan 2 nd scan FAST-KV SWITCHING DUAL-LAYER DETECTOR 4

5 Dual-source DECT DUAL-SPIRAL (no filtration) DUAL-SOURCE (with filtration) Cone-beam DECT 5

6 10/31/17 SECT calibration H&N patient scanned at 120 kvp 6

7 CT IMAGE DEPENDS ON THE X-RAY ENERGY CT IMAGE DEPENDS ON THE X-RAY ENERGY *Images from Johnson TRC, AJR 2012; 199:S3 S8 7

8 Soft tissue Density (g/cm 3 ) Elemental Compositions Breast 0.98 Hydrogen 8.97% Oxygen 71.13% Carbon 16.45% N, Mg, Cl, Ca Brain Hydrogen 9.97% Oxygen 72.13% Carbon 16.34% N, Cl Liver Hydrogen 8.4% Oxygen 68.41% Carbon 18.5% N, Mg, Cl, Ca Effective Atomic Number *Inserts GAMMEX RMI 467 phantom 16 ICRU H&N Tissues 1D-space 2D-space 8

9 16 ICRU H&N Tissues 1D-space 2D-space Soft tissue differentiation Stopping power ratios calculation BETHE FORMULA Mean excitation energy of the medium (ev) Relative Electron Density Mean excitation energy of water (ev) Proton energy (MeV) 9

10 Stopping power ratios calculation SECT BETHE FORMULA CT # to relative electron density Bragg Rule CT# to SPR curve Stopping power ratios calculation DECT BETHE FORMULA Yang, PMB 2010 (Saito et al, MP 2012) Effective Atomic Number (Landry et al, PMB 2013) (Saito et al. MP 2016) 10

11 10/31/17 MATERIAL AND DENSITY MAPS SPR MAPS COMMERCIALLY AVAILABLE TPS MONTE CARLO CALCULATIONS (for now) DECT IN PROTON THERAPY Implementing DECT in PT DECT ACQUISTION SPR MAPS IMAGE RECONSTRUCTION DECT OUTPUT IMAGED-based PROJECTION-based MATERIAL / DENSITY MAPS DOSE RANGE *Courtesy of Gloria Vilches Freixas 11

12 Taasti et al 2017 Implementing DECT in PT Hudobivnik et al 2016 Wohlfahrt et al 2017 Zhu and Penfold 2017 DECT ACQUISTION SPR MAPS Bär et al 2017 IMAGE RECONSTRUCTION DECT OUTPUT DOSE RANGE IMAGED-based PROJECTION-based Vilches-Freixas et al 2017 MATERIAL / DENSITY MAPS Almeida et al 2017 Li et al 2017 Dose differences DECT vs SECT Zhu and Penfold, Med Phys 2016;43:2845 Scans CIRS for calibration DECT and SECT images of Catphan Dose distribution in a donut target 12

13 Dose differences DECT vs SECT Zhu and Penfold, Med Phys 2016;43:2845 SECT DECT Maximum dose difference 7.8% 1.4% Root mean square error 2.1% 0.4% SECT DECT Range shifts between HU-SPR LUT and DECT patient specific SPR prediction Wohlfart et al IJROBP 2017 (II) Follows the work from: Wohlfahrt et al IJROBP 2016 Wohlfahrt et al IJROBP 2017 (I) Proof of concept with anthropomorphic phantom DECT proofed to be more accurate than SECT 13

14 Uncertainties related to SPR estimation from DECT Li et al. Phys Med Biol 2017;62: Why factors that contribute to the SPR uncertainty from the DECT-based approach How Dual-source FORCE comparison of two DECT methods Uncertainties imaging modelling inherent composite range uncertainty Results Methods: similar results overall uncertainty: 3.8% lung, 1.2% soft, 2.0% bone tissues. Dominant factor: imaging uncertainties IMAGING TECHNOLOGY PHYSICS TPS Variation of CT number is amplified in DECT process Detectors / Reconstruction algorithms Uncertainty on I-values of the atomic elements and I-value of water Inclusion of DECT images 14

15 DECT for Proton Therapy? Improved accuracy: Relative Electron Density YES! Improved tissue segmentation DECT for Proton Therapy Improved accuracy: range prediction Improved image quality for delineation 15

16 MAASTRO - Physics Research Group isabel.dealmeida@maastro.nl Thank you! More references Hudobivnik et al. Med. Phys (1) Taasti et al. Med. Phys (10) Bär et al. Med. Phys Jun;44(6): Möhler et al. Phys Med Biol Jun 7;61(11):N Wohlfahrt et al. Int J Radiat Oncol Biol Phys ;97(2): Vilches-Freixas et al. Med. Phys (9):