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Aspetti fisici della radioterapia moderna - II: Treatment planning, IMRT, protoni Marco Schwarz Agenzia Provinciale per la Protonterapia.

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Presentazione sul tema: "Aspetti fisici della radioterapia moderna - II: Treatment planning, IMRT, protoni Marco Schwarz Agenzia Provinciale per la Protonterapia."— Transcript della presentazione:

1 Aspetti fisici della radioterapia moderna - II: Treatment planning, IMRT, protoni Marco Schwarz Agenzia Provinciale per la Protonterapia Trento, Italy 23 Settembre 2010

2 Treatment Planning in 3D CRT

3 3D CRT Target defined in soft tissues on CT images Higher target/OAR doses than in 2D CRT 3D Treatment planning Safety margins must be considered while designing treatment field ICRU 50(1993) and ICRU 62(1999) set the standard for dose planning and dose reporting reference volumes.

4 PTV concept: pros Forced people to explicitely incorporate geometrical uncertainties into treatment planning Very appropriate tool for CRT: not too simple, not too complex. CTV = Clinical Target Volume (visible + microscopic disease) PTV = Planning Target Volume

5 Margin recipes Analytical solution for spherical targets (van Herk 2000) Derived/verified with simulations for real cases (e.g. Stroom 1999, Van Herk 2002) as a function of population-based data on geometrical uncertainties

6 Different 'recipes' according to the desired probability level PTV planning= same dose prescription for all points above a given probability of presence for target cell

7 PTV: cons Use of accurately defined margins still quite rare Dose homogeneity in the PTV became a must more for technical than for clinical reasons N.B. IGRT mostly aims at reducing PTV margins without radically changing PTV-based RT techniques Most important: the PTV concept works only if three assumptions are valid:

8 PTV - playing by the rules The PTV is a tool for dose planning and dose reporting. There are three underlying assumptions: 1. The dose distribution is invariant for (small) translations and rotations 2. The margins are chosen appropriately as a function of the geometrical uncertainties one wants to compensate for 3. The dose distribution in the PTV is as homogeneous as possible. Condition1 is granted using photons, 2 and 3 must be ensured using correct planning practices.

9 + PTV expansion = ? As if one should prefer homogeneous doses in the wrong PTV instead of heterogenous doses in the right PTV CTV OAR CTV OAR

10 Treatment planning in IMRT

11 More degrees of freedom More need to know what you want CRTIMRT

12 How to tell a machine what we want from it ?

13 Still struggling with TP in IMRT Adapted from Das et al, JNCI 2007 Inst.1Inst. 2Inst. 3Inst. 4Inst. 5

14 In IMRT si hanno molti più gradi di libertà che in CRT, troppi per poter essere gestiti a mano. Gli scopi del trattamento devono essere espressi in un linguaggio comprensibile tanto dalluomo quanto dalla macchina Lottimizzazione in IMRT è la gestione via macchina di una serie di obiettivi intrinsecamente in contraddizione.

15 Funzione di costo Traduzione quantitativa delle caratteristiche del piano di trattamento in termini di Traduzione quantitativa delle caratteristiche del piano di trattamento in termini di – Obiettivi di dose (e.g. Dmin, Dmax) – Intenti del trattamento (e.g. controllare la dose vs. massimizzarla/minimizzarla) – Trattamenti precedenti – Informazioni biologico/funzionali – Informazioni geometriche (e.g. errori di set-up) – Parametri di erogazione – …

16 The objective cost function 1. Evaluator Quantifies a relevant feature of the plan Dmean Dmin/Dmax DVHpoint # segments treatment time plan robustness … 2. Modifier A function f of the difference between the actual (E) and the desired (E 0 ) value of the evaluator

17 3-step IMRT treatment planning 1. Fluence optimization Cost function minimization Up to 10^4 beamlets Dose calc: fast but not very accurate 2. Segmentation Mechanical and dosimetrical MLC parameters are included Deterioration of the dose distribution 3. Final dose calculation No reoptimization Dose calculations: slower, but more accurate than in step 1.

18 Aperture based treatment planning 1. Initial fluence optimization 2. Initial Segmentation 3. Tuning of a deliverable plan Taking benefit of degeneracy --> More efficient delivery Less computational burden = Possibility of using accurate dose algorithms

19 Patient specific QA What do we talk about when we talk about ?

20 Dont forget the big picture Huq et al, IJROBP (1) Supp.

21 2-D dosimetry + gamma analysis What is patient specific in this approach? The beam setting Which aspect of the treatment chain is evaluated? The head model In most cases, field by field analysis Some techniques require whole treatment verification (e.g. VMAT)

22 Monte Carlo dose calculation (Tübingen) Main advantages 1)It solves the main dosimetric problem of IMRT dose calculation algorithms (source model) 2)Combined with hardware QA, it allows to come back to separate hw e sw QA, as in CRT

23 -evaluation EPID portal dose (2D imager plane) EPID dose (2D patient mid-plane) back-projection EPID treatment image (2D) separate fields, 2D Planning CT (3D) Planning dose (2D patient mid-plane) select mid-plane slice Planning dose (3D) Courtesy B. Mijnheer In-vivo dosimetry(NKI)

24 Dose-based corrections protocols? Planning CT + Planned dose CBCT + In vivo dosimetry Gamma analysis: dose errors Vs anatomy changes McDermott, R&O2008

25 Delivery

26

27 Tecniche ad arco. Perché? Aumento numero di campi >> aumento gradi di libertà Migliore conformazione della dose In caso di target concavi migliore risparmio degli OAR Erogazione più veloce e riduzione movimenti intra-fraction Molti parlano inoltre di migliore efficienza e riduzione MU, ma laffermazione è discutibile From De Neve, in Image-guided IMRT, Springer Ed. 2007

28 Time/efficiency

29 Treatment complexity vs monitor unit Bakai et al, PMB 2003 s=1-D max /D presc

30 2-step IMRT treatment planning 1. Fluence optimization Cost function minimization Up to 10^4 beamlets Dose calc: fast but not very accurate 2. Segmentation Mechanical and dosimetrical MLC parameters are included Deterioration of the dose distribution 3. Final dose calculation No reoptimization Dose calculations: slower, but more accurate than in step 1.

31 Aperture based treatment planning 1. Initial fluence optimization 2. Initial Segmentation 3. Tuning of a deliverable plan Taking benefit of degeneracy --> More efficient delivery Less computational burden = Possibility of using accurate dose algorithms

32 Author Mu S- IMRT MU VMAT1 Mu VMAT2 MU CRT Time S- IMRT Time VMAT1 Time Vmat2 Palma IJROBP Verbakel IJROBP Cozzi R&O Vanetti R&O Clivio R&O Nicolini Rad On Shaffer IJROBP 2009 (E-pub) Zhang IJROBP 2009 (E-Pub) Shaffer Clin Oncol

33 Cone Beam Dose erogata in una singola/multipla rotazione del gantry Durante la rotazione la fluenza è modulata: - Variazione forma del campo(movimento lamelle MLC) - Variazione dei pesi dei campi (variazione di intensità) Fan Beam Dose erogata grazie ad un fan beam che ruota continuamente in concomitanza alla traslazione del lettino Durante la rotazione la fluenza è modulata: - Variazione forma del campo - Variazione dei pesi dei beamlets Tecniche Conformal Arc, AMOA, IMAT, VMAT Tomoterapia seriale/elicoidale

34 IMRT (Angoli fissi) IMAT (Archi multipli) VMAT Single arc

35 Tomoterapia Il gantry ruota per 360° creando 51 proiezioni Modulazione ottenuta variando il tempo di On/Off per ogni lamella Velocità di rotazione del gantry e tempo di trattamento dipendono da: dose di prescrizione, lunghezza target, dose rate

36 Single/Few Arc(s) vs TOMO

37 Prostata HT e IMAT: distribuzioni comparabili; IMAT: erogazione più veloce IMAT: riduzione dose integrale Canale Anale HT: migliore qualità piani; migliore copertura e omogeneità target; migliore risparmio genitali H&N HT: migliore qualità piani gradiente di dose più elevati Solid line: IMAT

38 Interplay effects Bortfeld et al, PMB 2002 Is it that bad ? It depends Could we solve it by adding a margin ? No (Not completely)

39 Intrafraction (interplay) effects Jiang et al, PMB fr30 fr1fr30 fr sw s&s10 s&s20

40 New treatment modalities

41 Radiation delivery technologies HDR 'Conventional' XRT Tomotherapy IMXT 'Conventional' p+ Heavier ions(?) Tomorrow's ideas

42 Where would we like to use p+ ? In principle, for all patients In practice, whenever dose sparing at all dose levels could make the difference 3DCRTTOMO 10% Dose 35%D ose % Gy IMPT 0% Dose

43 The Bragg peak

44 Protons vs photons – Version 2

45 Protons vs photons – version Protoni Fotoni

46 Protons vs photons – version 4 X p+ + 3D modulation + Steep dose fall off = More degrees of freedom

47 IMRTIMPT Protoni vs. Fotoni – caso pediatrico G. Fava - ATreP

48 IMRTIMPT

49 Sezione assiale con aree di basse dosi IMRT IMPT

50 Dosimetric effects of geometrical uncertainties No errors 10mm setup 5mm setup 5mm setup 10 mm respiration M. Engelsman - MGH

51 X rays protons

52

53

54 Our choices Our choices PT center as the first module of a new public regional hospital Emphasis on availability and clinical usability No significant local development on PT technology Delivery mode: PBS only Interest in patient set up outside the treatment room First treatments: first half of 2013(?)


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