Treating moving organs with particle beams Christoph Bert GSI Helmholtz Centre for Heavy Ion Research, Department of Biophysics Darmstadt, Germany
Organ motion in radiotherapy A. Constantinescu Heart beat Friday, 9:30h Scale: seconds A. Rucinski Gut motion Prostate Gas Friday, 16:12h Scale: minutes 2
Organ motion in radiotherapy Respiration in particle therapy Respiration Scale: seconds 10cm 2cm 4cm 6cm 8cm tumor beam range 3
Respiratory motion - beam range [courtesy S.O. Grözinger, GSI] 12 C dose photons range ⇒ mitigation of range / longitudinal changes essential 2/28/2012 ICTR-PHE, Geneva 2012 4
Mitigation by margins (ICRU recommendation) ITV Internal target volume GTV Gross tumor volume [Rietzel et al., MGH] CTV Clinical target volume PTV Planning target volume 2/28/2012 ICTR-PHE, Geneva 2012 5
Range change dependence of margins Original treatment plan Original TP to 5 mm shifted tumor ⇒ Margins have to incorporate range and are thus field specific [M. Koto et al. / Radiotherapy and Oncology 71 (2004)] 2/28/2012 ICTR-PHE, Geneva 2012 6
Margins incorporating range changes • Propage CTV to ITV by manual exchange of HU-numbers (i.e. replace lung tissue by tumor tissue) [Koto et al. 2004] • Scattered beams: Change of compensator + aperture to cover all motion states of 4DCT [Engelsman et al. 2006, Mori et al. 2008] mitigation needed additional motion • Beam scanning, single field: ITV = union of CTVs in water-equivalent space [Bert & Rietzel 2007] • Beam scanning, IMPT: Beam specific WEPL-LUT and common geometric ITV [Graeff et al., GSI] 2/28/2012 ICTR-PHE, Geneva 2012 7
Water-equiv. Path Length ITV ITV Geometry WEPL-LUT CTV bone Water-Equivalent Path Length Field 1 Field 2 A B C (ref) Union of A,B,C Geometric union in WEPL of C Motion Phase [Graeff et al., GSI] 2/28/2012 ICTR-PHE, Geneva 2012 8
Field specific WEPL-LUT [Graeff et al., GSI] 2/28/2012 ICTR-PHE, Geneva 2012 9
Static Dose: DVH End Exhale (Reference) End Inhale [Graeff et al., GSI] 2/28/2012 ICTR-PHE, Geneva 2012 10
Static Dose: ITV Comparison Range-ITV Geo-ITV End-Inhale [Graeff et al., GSI] 11 2/28/2012 ICTR-PHE, Geneva 2012
4D-Dose (15 rescans): ITV Comparison Range-ITV Geo-ITV [Graeff et al., GSI] 12 2/28/2012 ICTR-PHE, Geneva 2012
4D-Dose (15 rescans): DVH [Graeff et al., GSI] 13 2/28/2012 ICTR-PHE, Geneva 2012
Interplay - simulation data → IM / ITV / PTV not sufficient [Bert et al, Phys Med Biol, 2008] 2/28/2012 ICTR-PHE, Geneva 2012 14
Motion mitigation techniques • Rescanning [Phillips et al., Phys Med Biol 1992] • multiple scans of ITV • several modalities investigated recently [Seco et al. 2009, Furukawa et al. 2010, Zenklusen et al. 2010] • Beam Tracking [Grözinger et al., Phys. Med. Biol. 2006] • compensate target motion by real-time adjustment of Bragg peak • 4D treatment plan optimization required • Gating [Minohara et al., IJROBP 2000] • beam on, if tumor within gating window (e.g. 30% around end-exhale) • used at NIRS for scattered beams >10 years • reduced ITV size • beam scanning: mitigation of residual motion 2/28/2012 ICTR-PHE, Geneva 2012 15
Motion mitigation techniques • Abdominal compression • supress motion • used at HIT for treatment of hepato cellular cancer • scanned beam: influence of residual motion • Apnea • anesthetized and intubated patient • used at RPTC, Munich since > 1 year • Breath hold • could be an option for sites with fast delivery (e.g. PSI with 80ms energy change time or NIRS with energy change on flat-top) 2/28/2012 ICTR-PHE, Geneva 2012 16
Rescanning [courtesy of A. Knopf, PSI and Knopf et al. Phys Med Biol 2011] 2/28/2012 ICTR-PHE, Geneva 2012 17
[courtesy of A. Knopf, PSI and Knopf et al. Phys Med Biol 2011] 2/28/2012 ICTR-PHE, Geneva 2012 18
[courtesy of A. Knopf, PSI] 2/28/2012 ICTR-PHE, Geneva 2012 19
Beam Tracking • Incorporated into GSI TPS TRiP4D [Bert & Rietzel, Radiat Oncol 2007; Saito et al.. Phys Med Biol 2009; • Implemented and experimentally validated at GSI for C12 irradiations of simple geometries • Procedure: pre-calculate compensation data for each combination of beam position and 4DCT motion state Bert et al. Med Phys 2007] 2/28/2012 ICTR-PHE, Geneva 2012 20
Real-time dose compensated beam tracking (RDBT) • Dose change depends on temporal correlation between beam and tumor motion • Real-time dose compensation necessary (RDBT) – Beam tracking: change of beam position and energy – RDBT: additionally change of deposited dose i.e. change of all treatment plan parameters based on target motion state and pre-calculated data [Lüchtenborg et al. Med. Phys. 2011] 2/28/2012 ICTR-PHE, Geneva 2012 21
Beam tracking technique comparison [Lüchtenborg PhD-Thesis 2011] Stationary dose distribution • Treatment planning study (TRiP4D) Patient #5 based on 4DCT data of 5 patients (courtesy MDACC, L.Dong) • Modalities • Beam Tracking (BT) • RDBT (dose compensated BT) • lateral BT (no range compensation) • interplay RDBT interplay • Plan design: • 4 fields, 4 fractions • 8.2 Gy (RBE) / fraction • based on NIRS protocol V95 • 81 motion combinations calculated • Report of V95 2/28/2012 ICTR-PHE, Geneva 2012 22
4D dose calculation: beam tracking [Lüchtenborg et al., PhD-Thesis, 2011] 2/28/2012 ICTR-PHE, Geneva 2012 23
Results V95 • BT and RDBT yield CTV coverage (with RBE-weighted dose) • RDBT not essential for lung cancer treatment • lat. BT sufficient for some patients [Lüchtenborg PhD-Thesis 2011] 2/28/2012 ICTR-PHE, Geneva 2012 24
Gating: clinical for passively shaped beams • NIRS (Chiba, Japan) uses gating for respiration influenced tumors since >10 years • Passively shaped carbon beams – No interference with target motion / simultaneous irradiation – Margins/PTV to account for motion amplitude – Compensator smearing to account for range changes • Great clinical results for lung cancer – Dose escalation studies – Hypo-fractionation studies [Minohara et al., IJROBP 2000, Miyamoto et al., Radioth. Oncol. 2003, IJROBP 2007, Mori et al. IJROBP 2008 ] 2/28/2012 ICTR-PHE, Geneva 2012 25
Gating: Residual motion – scanned beams Irradiation under abdominal compression, e.g. liver cancer (HCC) similar residual motion residual motion (gating) amplitude � <~10mm residual motion (abd. compr.) time � mitigation & robustness studies needed! 2/28/2012 ICTR-PHE, Geneva 2012 26
Residual Motion Mitigation � Optimize beam overlap: ( Δ S = grid spacing) F (FWHM) = 5 x Δ S Δ S F = 3 x Δ S Δ S (standard) beam spots [Bert et al., IJROBP 2010] 2/28/2012 ICTR-PHE, Geneva 2012 27
Residual Motion Mitigation � ripple larger peak width B filter width B beam energy layers spacing ∆ Z reduced slice spacing ∆ Z modulated bragg peak width increased longitudinal overlap [courtesy D. Richter, GSI] 2/28/2012 ICTR-PHE, Geneva 2012 28
Gating-Experiments at HIT Measured: Anzai- Laser Sensor • ellipsoidal target volume Robot • 3D target motion • 18 beam overlap parameter combinations Laser Sensor • motion amplitutes up to 10 mm ⇒ ∼ 90 different parameter combinations Simulated (TRiP4D): 24 Ionisation Chambers • additional motion amplitudes • 4 – 30 starting phases ⇒ ~ 900 different parameter combinations Beam Target Volume Geiger Counter 2/28/2012 ICTR-PHE, Geneva 2012 29
Influence of residual motion CTV PTV [Steidl, Richter, Gemmel, Bert, GSI/Siemens] 2/28/2012 ICTR-PHE, Geneva 2012 30
Validation: Measured vs. TRiP4D calculated � Amplitude: 4mm (peak-peak) mean deviation : 2.5 ± 2.2 % beam Absolute Deviation Amplitude: 10mm (peak-peak) 24 ionization mean deviation: 0.0 ± 3.3% chambers ⇒ validated simulations [Richter et al, Radioth. Oncol. 96 (S1) 2010] 2/28/2012 ICTR-PHE, Geneva 2012 31
Example: Variation of beam focus homogeneity F=5 mm F=8 mm F=10 mm variation of ϕ 0 residual motion [mm] [Steidl, Richter, Gemmel, Bert, GSI/Siemens] 2/28/2012 ICTR-PHE, Geneva 2012 32
Beam parameters – results Variation Variation Variation Variation grid spacing beam focus IES spacing Bragg-Peak-width slope of linear fit [mm -1 ] Order of influence: beam focus F > IES spacing Δ Z > grid spacing Δ S > Bragg-Peak width B [Steidl, Richter, Gemmel, Bert, GSI/Siemens] 2/28/2012 ICTR-PHE, Geneva 2012 33
Hepato Cellular Cancer treatment at HIT • HCC treatments started ~ 6 month ago, 6 patients so far • Protocol based on NIRS experience • 4 fractions each 8.1 Gy (RBE) (LEM I) ANZAI belt • Beam delivery • abdominal press (5 pat.) • Gating (1 pat.) • Motion surrogate: ANZAI belt • Treatment QA • 4DPET Ch. Kurz, Friday 12:00h • reconstruction of daily 4D dose distribution 2/28/2012 ICTR-PHE, Geneva 2012 34
Example – abdominal compression Δ s=2mm, Δ z=3mm, F=10mm Δ s=2mm, Δ z=3mm, F=6mm [Richter, Härtig, Chaudhri, et al., GSI/HIT/RadioOnkol] 2/28/2012 ICTR-PHE, Geneva 2012 35
Example – Gating – 3D dose CTV PTV [Richter, Härtig, Chaudhri, et al., GSI/HIT/RadioOnkol] 2/28/2012 ICTR-PHE, Geneva 2012 36
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