SGRT Community Meeting 2021 Presentation by: Stewart Gaede, PhD MCCPM​ Chief Medical Physicist​ London Regional Cancer Program

1. SBRT: The Importance of Continuous Motion
Management
Stewart Gaede, PhD MCCPM
Chief Medical Physicist
London Regional Cancer Program
April 23, 2021

2. Disclosures: Nothing to Disclose
BIOPHYS 9507B

3. London Regional Cancer Program (LRCP)
• The primary academic regional cancer
provider for Southwestern Ontario
• Provides a comprehensive range of cancer
care services to approximately 1.5 million
people
• Approximately 4500 patients per year with
radiation therapy
• 20 Radiation Oncologists, 13 Medical
Physicists, and 85 Radiation Therapists

4. London Regional Cancer Program (LRCP)
• 9 linear accelerators
– 4 Varian TrueBeams v2.7 (1 with HD-MLC)
• Real-time Position Management (RPM)
– Respiratory Gating
– Deep-Inspiration Breath Hold
– 4 Varian 2100 IX
– Tomotherapy
• 2 AlignRT systems
– 1 Standard TrueBeam
– 1 TrueBeam with HD-MLC
• 3 GateCT systems
– 2 Philips Wide-Bore CT simulators
– 1 GE Revolution CT Scanner (offsite research CT
scanner)

5. Learning Objectives
1. Recap the evolution of SABR
2. Briefly describe motion management strategies
3. Feasibility and Reproducibility of Surface-Guided RT (SGRT)
for SABR
– Both free breathing and DIBH
4. Considerations when implementing SGRT and SABR

6. Evolution of SABR
• Stereotactic Ablative Radiotherapy (SABR) has become standard of care for
inoperable Stage 1 NSCLC
• SABR has also emerged as an effective treatment of oligometastatic disease
• SABR has seen world-wide implementation due to technological advances:
– 4D-CT
– 3D and 4D Image-Guided Radiotherapy (IGRT)
• Allowed for consideration of frameless delivery
– Volumetric Modulated Arc Therapy (VMAT) and Flattening-filter Free (FFF) beams

7. • Sonke et al 2009
• Used 4D-CBCT acquired
before and after
treatment to verify that
Frameless SABR is safe

8. Evolution of SABR
• Despite technological advances, respiratory motion management is still
challenging
• Motion encompassing methods such as 4D-CT
– Allows for patient-specific tumour size, shape, and respiratory motion to be accounted
for in the planning target volume (PTV)
– However, patients exhibiting large respiratory motions have:
• Increased irradiated volume of normal lung within the PTV
• PTVs become closer to other organs-at-risk (OARs)
• Potentially lower radiation dose to the tumour than prescribed due to interplay effects of
IMRT/VMAT
– Not all patients breathe reproducibly causing unwarranted motion artifacts

9. Other Motion Mitigation Strategies
• Tumour Immobilization Methods
– Ex. Civco Body Pro-lok, Elekta BodyFIX
• Respiratory Gating Methods
– Ex. Varian Real-Time Position Management
• Tumour Tracking Methods
– Ex. Cyberknife, Calypso
• Involuntary Breath-Hold Methods
– Ex. Active Breathing Control (ABC)

10. Voluntary Breath Hold Techniques
• Varian RPM System
• Tracks one point on a patient surface
– Does not differentiate between true DIBH and
other patient movement (ex. back arching)
• SGRT (Ex. AlignRT)
• Directly measures patient chest wall and
abdominal motion
– Simultaneously tracking multiple points within a
region of interest (ROI)
– Assess translation and rotation

11. SGRT and SABR
• SGRT has been validated extensively as a method to:
– Improve patient setup prior to treatment for many sites
– Continuously monitor patients during treatment
• No ionizing radiation-based imaging and/or implanted fiducial markers
• Facilitated the use of DIBH for breast cancer
• Facilitated frameless stereotactic radiosurgery for brain
• Less data exists for implementation of SGRT for setup/monitoring of
intrafraction motion during SABR

12. SGRT and SABR
• Heinzerling et al (2019) showed that
CBCT shifts after SGRT-based setup
were small
– <5mm and 0.5 degrees in all directions
• Continuous monitoring allowed for
repeat CBCT when >2mm was detected
– 25 out of 34 patients had additional shifts
of at least 2mm
– No significant difference between resulting
SGRT and CBCT shifts
– SGRT during treatment may detect
clinically meaningful intrafraction motion

13. SGRT and DIBH-SABR
• Limited data for SGRT and DIBH for
SABR
• Naumann et al (2020) assessed the
feasibility and reproducibility
– Repeat CBCT after shifts and prior to
treatment
– 1 of 9 lung fxs required added shift
(>2mm)
– 7 of 34 liver fxs required added shift
– Intrafraction difference of 1.6mm (lung)
and 1.2mm (liver)
– Interfraction difference of 0.9mm (lung)
and 3.8mm (liver

14. • Indications for SABR-LUNG at LRCP
– Inoperable Stage I Non-small cell lung cancer (NSCLC) (Current standard of care)
– Oligometastatic Disease
• SABR-COMET-3, SABR-COMET-10
– SABR-BRIDGE
• Operable Stage 1 NSCLC where surgery was delayed due to pandemic based OR closures
• Radiation Dose based on a risk-adapted approach (tumour size, location)
– 54Gy in 3 fractions
• T1 tumours (≤3cm) surrounded by lung parenchyma
– 55Gy in 5 fractions
• Tumours ≥3cm or with chest wall contact
– 60 Gy in 8 fractions for tumours < 2cm of the mediastinum or bplexus
SABR-LUNG Program at LRCP
34 Gy in 1 fraction

15. SABR-LUNG Program at LRCP
CT Simulation Protocol
• Civco Vac-lok immobilization
– Arms above head (Get pic if
possible)
• DIBH Fast Helical CT scan
• 4D-CT Scan
• Motion monitoring with Varian
RGSC System
– Moving to GateCT when AlignRT
available on all of our TrueBeam
Systems

16. SABR-LUNG Program at LRCP
Respiratory Motion Management
• If respiratory motion of the tumour in any direction < 5mm
– Free Breathing unmonitored radiotherapy on any linac
– AlignRT used for setup for patients scheduled on AlignRT machines
– 3D-CBCT sufficient for soft-tissue matching
• If respiratory motion of the tumour in any direction >= 5mm and <= 15mm
– Free Breathing radiotherapy using wide amplitude gating technique
• 100% gating window (gates out larger than intended motion amplitudes and irregularities
– 4D-CBCT for IGRT
– AlignRT Setup/Monitoring of patients scheduled on AlignRT machines
• If respiratory motion of the tumour in any direction > 15mm or better OAR sparing is
achievable
– DIBH with AlignRT

17. Considerations for SGRT and DIBH-SABR
Patient Selection and Simulation
• Patient compliance for DIBH different for lung SABR vs. left-sided
breast patients
– Pulmonary function often poorer for lung patients
• Increase in total treatment times
– 7.5Gy – 34Gy per fraction for SABR vs. 2Gy - 2.65Gy per fraction for
left-sided breast patients
• Multiple breath-holds are required
• Longer training session required during CT simulation
– Perform multiple practice DIBHs before 15-20 sec DIBH CT scan

18. Considerations for SGRT and DIBH-SABR
Treatment Planning
• Free Breathing RT
– Motion encompassment via 4D-CT
• Untagged average CT
– Low-pitch Helical CT dataset acquired for 4D-CT
reconstruction
• Fuse end inhale and end exhale scans
• PTV = GTV(inhale) + GTV(exhale) + 5mm
• VMAT treatment planning
– 2 6X-FFF Partial Arcs (~225o)
• DIBH RT
• DIBH-CT for planning
• PTV = GTV(DIBH) + 5mm
• VMAT treatment planning
• 2 6X-FFF Partial Arcs (~225o)

19. Considerations for SGRT and DIBH-SABR
Treatment Planning

20. Considerations for SGRT and DIBH-SABR
ROI Definition
• ROI definition for DIBH vs Free Breathing SABR patients
• Include areas where external contour differs between FB and DIBH datasets
– Lateral sides of the patient
– Lower thorax with small distance from isocentre

21. Considerations for SGRT and DIBH-SABR
Image-Guidance
• kV-CBCT imaging limited due to camera blockage
– Create an ROI that is for monitoring CBCT acquisition only away from isocenter to
lower thoracic region
– Impact of Couch Centering for peripheral lesions
• Create a couch centering field in the record workspace
• Capture a reference image on Day 1
• Draw CBCT monitoring ROI

22. Considerations for SGRT and DIBH-SABR
Image-Guidance
• AlignRT does not trigger kV beam:
– Unable to perform 4D-CBCT for free breathing patients
– Manual triggering of kV beam during DIBH-CBCT
– Monitor Diaphragm position during acquisition and manually beam off when position changes
– Spotlight CBCT often used to minimize scan time
Cameras unblocked – In tolerance Cameras blocked – In tolerance

23. Considerations for SGRT and DIBH-SABR
Treatment Monitoring
• During treatment kV imaging limited due to camera blockage
– How can we ensure the internal target is being treated accurately during DIBH treatment?
– kV triggered imaging with increased SAD for kV imaging arms (170cm)
– MV triggered imaging (cine EPID)

24. Discussion
• Positive transition from marker block based SABR treatments to SGRT
based treatments
• Considerations that needed addressing before successful implementation
– Patient Compliance for DIBH
– Region(s) of Interest accounting for:
• DIBH surface changes
• Camera blockage during kV acquisition
• Couch centering
– Inability of AlignRT to trigger kV imaging beam
• Careful attention during CBCT acquisition
• Use of MV cine EPID to ensure treatment accuracy

25. Current Work
• Use of during treatment cine EPID to quantify intrafraction motion during
DIBH-VMAT to determine reproducibility
• Quantitative measures such as centroid motion or Dice coefficients between the planned GTV
position and actual GTV position.
• Verify GTV position is inside PTV for all beam-on time points where the target is visible.
– Correlated to PDATA from AlignRT
Fraction 1 Fraction 2

26. Conclusions
• Surface-guided radiation therapy is a feasible and reliable solution for
setup and monitoring of lung lesions receiving SABR
• Can reduce amount of immobilization
• Facilitates DIBH for minimizing intra-fraction motion
– Requires accurate 3D setup imaging and intrafraction monitoring to ensure
accurate treatment delivery

27. Acknowledgments
Radiation Therapy:
Jenny Mickle
Krista D’Angelo
Angela Rulton
Stacie Nesbitt
Jessica Hinton
Melissa O’Neil
Medical Physics:
Scott Karnas
Eric Wright
Derek Gillies
Radiation Oncology:
David Palma
Melody Qu
Joanna Laba
Brian Yaremko
George Rodrigues
Edward Yu
Acknowledgments