Physics. Sunday, March 4, :30 a.m. 10:00 a.m.

Transcription

1 Physics Sunday, March 4, :30 a.m. 10:00 a.m.

2 Social Q&A Use your phone, tablet, or laptop to Submit questions to speakers and moderators Answer interactive questions / audience response polls astro.org/refreshersocialqa

3 Faculty Disclosures Faculty and Committee disclosures are also on the 2018 ASTRO Annual Refresher Course website. Name Employment Funding Sources Ownership or Investments Laurence Court, PhD MD Anderson Cancer Center Leadership None None None

4 Physics: MRI-guided Radiation Therapy Laurence Court, PhD University of Texas MD Anderson Cancer Center Houston TX

5 Disclosures Employer: UT MD Anderson Cancer Center Grants from: NCI, CPRIT, Varian, Elekta, Mobius

6 Acknowledgements Many slides from Geoff Ibbott, Carri Glide-Hurst, Dave Fuller, Ashley Rubinstein, Gabriel Sawakuchi, Daniel O Brien, Bas Raaymakers, Elekta and ViewRay

7 Learning Objectives To be able to describe the different approaches to MRI-guided radiation therapy To be able to discuss some of the dosimetric challenges with MRIguided radiation therapy (treatment planning, physics QA..)

8 Contents Why MR-guided RT? What does MR-guided RT look like? What is the impact of the magnetic field on distributions? What ways are there to mitigate this? Anything else to worry about (radiation biology experiments) Some physics QA challenges How many patients have been treated? Summary

9 Why MR for RT? Very brief introduction to what MR can offer us

10 What clinical benefits could MR bring to radiotherapy? Slide from Dave Fuller

11 Why should the future be MR? Fundamental advantage: Simultaneous imaging of not only anatomy, but of functional and spatial/motion of both tumor and normal tissue over time Ultimately, we want data that is: Anticipatory (predictive/early) Actionable (changes care) Accurate (in time and 3D space) Additive (more than 1 feature/function) Slide from Dave Fuller

12 Role of MRI is growing in Radiation Oncology Expansion to Treatment Time imaging Diagnosis Staging Simulation Treatment Planning Tx Delivery On-Line Adaption & Tx Assessment Off-line Response Assessment MR Scanner MR Scanner w/ MR-RT Oncology Configuration Treatment Planning S/W with MR support MRI Guided Radiation therapy MR Scanner Sequences and Postprocessing S/W MR Images courtesy of Philips G. Ibbott, RSNA, Chicago, 2017

13 MRI-guided Radiotherapy Introduction to in-room MR-guided RT

14 Concept of MRI accelerator Accelerator MLC Simultaneous MRI and irradiation To do this: 1. Mount the Linac on a rotatable gantry around the MRI magnet The radiation isocentre is at the centre of the MRI imaging volume 2. Modify the linac to make it compatible with the MRI beam 3. Modify the MRI system to Minimise material in the beam path and ensure it is homogeneous Minimise magnetic field at the Linac Raaymakers et al. PMB 2009 Technical issues Magnetic interference Beam absorption RF interference Based on a slide from Elekta

15 Raaymakers et al. PMB cm central region free from coils 8cm Al eq Active magnetic shielding (pair of shield coils with opposite polarity)

16 Impact of magnetic field on dose distributions

17 Point dose kernels with and without a magnetic field Raaijmakers et al. PMB

18 Raaijmakers et al. PMB 2008 Dose deposition in a magnetic field The Electron Return Effect (ERE) B = 0 B = 1.5 T γ γ e- γ γ e- γ γ e- e- e- e-

19 Relative Dose (%) Dose perturbation effects 0 T 1.5 T B = 1.5 T B = 0 T Raaijmakers et al, Phys Med Biol, Depth (cm)

20 If field covers whole phantom.. Raaijmakers et al, Phys Med Biol, 2008

21 Impact of surface orientation Raaijmakers 2007

22 Varying exit angle Raaijmakers 2007

23 Magnetic-field-induced dose effects in lung 6 MV beam soft tissue lung soft tissue 1.5T B- field 23

24 Magnetic-field-induced dose effects soft tissue lung soft tissue Raaijmakers et al, PMB, 2008 Rubinstein et al, Med Phys,

25 8 MV Beam 25

26 Ways to mitigate the impact of the magnetic field on the dose distributions

27 Mitigating dose perturbations Magnetic field strength System geometry Treatment planning 27

28 Princess Margaret Hospital - MR on Rails G. Ibbott, RSNA, Chicago,

29 Impact of magnetic field strength

30 Lower magnetic field strength Viewray MRIdian: Three Co-60 sources and a 0.35 T MRI Dan Low, MRI Guided Radiotherapy,

31 Wooten et al, IJROBP 92, , 2015

32 Dan Low, MRI Guided Radiotherapy, 2017

33 Change system geometry The Cross Cancer Institute 6 MV/0.6 T Linac-MRI The Australian 6 MV/1 T MRI-Linac Parallel orientation Perpendicular orientation Keall et al, Semin Radiat Oncol,

34 Account for perturbations in treatment planning Parallel-opposed radiation beams IMRT Monte-Carlo-based treatment planning 34

35 Single beam Parallel-opposed beams Water Lung Water 5 cm beam Raaijmakers et al, PMB,

36 Volume (%) DVH for optimized dose distribution oropharynx Comparison between B = 0 T and B = 1.5 T Submand Left Submand Right Brain Myelum Parotis Left Parotis Right Dose (Gy) Raaijmakers et al. Phys. Med. Biol. 52 (2007) p

37 Mitigating dose perturbations - summary Magnetic field strength System geometry Treatment planning 37

38 Radiation biology experiments Impact of magnetic field on dose response

39

40 Mouse lung phantom Co-60, 1.5T Single beam Parallel-opposed beams 2.5 cm beam Rubinstein et al, Med Phys,

41 PA Irradiation AP Irradiation Block for Co-60 beam 5 cm diam. poles Electromagnet coils

42 The effect of a strong magnetic field on radiation-induced lung damage No Magnetic Field 9, 10, 10.5, 11, 12, 13 Gy dose groups 10 mice per group Magnetic Field 9, 10, 10.5, 11, 12, 13 Gy dose groups 10 mice per group Control 0 Gy 20 mice 140 Mice (C57L) C57L Mice: Acute pneumonitis Chronic fibrosis No pleural effusions 42

43 P e rc e n t s u rv iv a l P e rc e n t s u rv iv a l Post-irradiation survival C o n tro l S u r v iv a l: A ll m ic e 9 G y T G y G y - 0 T T G y T 1 1 G y - 0 T G y T 1 2 G y - 0 T G y T 1 3 G y - 0 T D a y s 1 3 G y T D a y s 43

44 % M ic e W ith In c r e a s e d R R In c re a s e d R e s p. R a te a t 5 M o n th s > 190 bpm T 1.5 T E D 5 0 (9 5 % C I) G y ( ) G y ( ) D o s e (G y ) 44

45 Pre-irradiation 5 months post-irradiation Pre-irradiation In c r e a s e d L u n g D e n s ity a t 5 M o n th s > 0.64 g/cm 3 % M ic e W ith In c re a s e d D e n s T 1.5 T E D 5 0 (9 5 % C I) G y ( ) G y ( ) D o s e (G y ) 45

46 % M ic e W ith R e d u c e d V o l R e d u c e d H e a lth y L u n g V o lu m e a t 5 M o n th s T < 0.42 cm T E D 5 0 (9 5 % C I) G y ( ) G y ( ) D o s e (G y ) 46

47 Radiation biology experiments (so far) Magnetic field dose not change response (cell experiments) Pre-clinical (murine) studies: Magnetic field had no impact on survival Magnetic field had small (2% or less), but significant impact on respiratory rate, lung density, and healthy lung volume

48 Impact on physics QA Impact of the magnetic field on physics QA equipment and measurements

49 Standard QA measurements Ion chamber in solid water or plastic phantom

50 Effect of magnetic field on dose measurements Meijsing et al, 2009

51 Meijsing et al, 2009

52 Relative Chamber Response More measurement effects 1.5% 1.0% IEC1997 requires <= 0.5% variation for reference dosimetry 0.5% 0.0% In Water Solid Water Phantom Variation of 1.3% -0.5% Chamber Orientation (deg) PTW Farmer Chamber Phantom: 30 x 30 x 15 cm 3 solid water Chamber: long-axis parallel to magnetic field SCD: cm Depth: 5 cm Water Phantom Variation < 0.3% Slide from O Brien and Sawakuchi

53 Monte Carlo No magnetic field beam (a) 0 orientation beam (a) 180 orientation Slide from O Brien and Sawakuchi

54 Monte Carlo 1.5 T Magnetic Field beam B (a) 0 orientation beam B (a) 180 orientation Slide from O Brien and Sawakuchi

55 Initial Testing of MR- Compatible ArcCheck QA Device Power supply moved away from detector Must use MV beam to position at isocenter Must calibrate in MR Linac beam G. Ibbott, RSNA, Chicago, 2017

56 MR-guided RT is already here

57 MR-Co 60 Clinical since Jan, 2014 January June 2016, 316 patients treated Online ART MR-IGRT (6 mos) Cine gating (9 mos)

58 HFHS MR-Linac Program Summary (ViewRay system) 07/19/17 to 01/23/18 47 Patients 687 tx fractions completed Maximum tx/day = % Treatment Distribution 6.4% 46.8% SBRT Conventional APBI 2% 2% 2% 2% 2% 6% 11% Treatment by Disease Site (%) 11% 26% Slide from Carri Glide-Hurst 17% 19% Male Pelvis Abdomen Lung Liver Pancreas Breast Chest Wall Esophagus Kidney Bone H&N

59 Key Points/Summary In-room MRI-guided radiotherapy is here, with more to come The permanent magnetic field can impact dose distributions and measurements These can be accounted for in several ways Radiobiology experiments do not indicate any clinically significant issues (although indicate careful observation of patients)