Tracking Intrafractional Motion for Linac-based SRS with SGRT and Machine Walkouts

Yunze Yang, PhD Assistant Professor of Clinical Radiation Oncology
University of Miami Sylvester Comprehensive Cancer Center

2. Tracking Intrafractional Motion for Linac-based
SRS with SGRT and Machine Walkouts
Yunze Yang, PhD
Assistant Professor of Clinical Radiation Oncology
Department of Radiation Oncology
University of Miami, Sylvester Comprehensive Cancer Center
SGRT US Annual Meeting, June 2024

3. TRACKING INTRAFRACTIONAL MOTION FOR LINAC-BASED SRS WITH SGRT AND MACHINE WALKOUTS
Disclaimer
•No conflict of interest
•Information provided in this session is from our
independent clinical experience

4. Gamma Knife
Benefits
“Gold Standard”
• Long track record
• Brain only radiosurgery
• Does anything in brain
• Most precise option
•Patients and MDs know the brand
Cons
•Slow
•Resource intensive
•Implies head frame
•Not highly utilized

5. INTRODUCTION: LINAC-BASED SRS AND HA
Linac-Based SRS and HyperArc
Images courtesy of Varian Medical Systems, Inc.
•MLC-Based non-coplanar delivery
•Frameless
•Single isocenter and multi-target SRS

6. Session 1
Considerations in SRS-HA treatment

7. CONSIDERATIONS IN SRS-HA TREATMENT
SRS Requirements
SRS-specific commissioning and audit
•Small field measurement: TG155
•Commission of couch and immobilization device
•Mechanical and image guidance (Winston Lutz)
•Motion management (OSMS, immobilization, post-
treatment CBCT)
Standardized procedure and workflow (SRS SOP)
•Imaging, registration, contouring, planning, QA,
delivery

8. CONSIDERATIONS IN SRS-HA TREATMENT
Positioning
Accuracy
•Resolution
•Registration
•Iso-center placement
Dosimetric
Accuracy
•Density override
•Couch insertion
We will hit our targetWe will put the exact dose to
where we want

9. •1 mm
•1 Deg
Tolerance
CONSIDERATIONS IN SRS-HA TREATMENT

10. Surface guidance radiation therapy
•Help with setup
•Real-time monitoring of intra-fractional
motion
•The accuracy in motion tracking
•Sensitivity limitation
•ROI
•Machine deviations
•Non-coplanar treatment
It is important to improve the sensitivity and clinical
understanding of the sub-mm signals

11. Session 2
Decomposing surface guidance signal with
machine walkouts

12. CONSIDERATIONS IN SRS-HA TREATMENT PLANNING
Method
•We analyzed ten SRS treatments including non-coplanar arcs tracked using a SGRT
system (Vision RT)
•The corresponding couch angle data was linked to the Winston-Lutz test of isocenter
shift from couch rotation
•Intra-fractional motion was extracted by subtracting couch walkouts
•We compared the tracked intra-fractional motion with post treatment CBCT
(postCBCT) shifts at zero-couch angle for verification.

13. Couch anglevertical longitudinal lateral yaw roll pitch mag
all0.07-0.16-0.06-0.09-0.06-0.100.54
00.01-0.02-0.020.01-0.03-0.030.22
450.07-0.21-0.20-0.04-0.13-0.050.64
900.130.20-0.20-0.05-0.13-0.170.74
2700.25-0.620.00-0.570.01-0.100.71
3150.02-0.290.07-0.08-0.01-0.190.57
Couch angle
04590270315
OSMS median shift
-1.5
-1
-0.5
0
0.5
1
1.5
2
vertical
longitudinal
lateral
magnitude
yaw
roll
pitch
•Largest deviation was
found at 90 and 270-
degree couch angle
Result

14. Lateral (Winston-Lutz)/mm
Lateral (Surface Guidance)/mm
Corr Coeff = 0.72
Longitudinal (Winston-Lutz)/mm
Longitudinal (Surface Guidance)/mm
Corr Coeff = 0.68
•Couch walkouts contributed to
SGRT signals
Result

15. Subtract couch walkouts and
compare the data with post-CBCT
Angle
(Deg)
Correlation coefficient of all 6 degree of freedom
Before couch-walkout
subtraction
After couch-walkout
subtraction
00.1830.528
450.1240.410
900.4150.276
270-0.2290.512
315-0.0660.524
Mean0.0860.450
Mean of correlation coefficient of the last treatment
Overall correlation coefficient = 0.53
•By decomposing the SGRT signal and
subtracting the systematic couch
walkout allows more accurate patient
intra-fractional motion

16. Isocenter Considerations of Multi-mets

17. SRS-HA TREATMENT PLANNING
Isocenter Considerations of Multi-mets
•Considering the rotational
uncertainty
•Isocenter-to-target distance should
< 6 cm
•Favoring small lesions to the large
ones
•Place isocenter closer to small mets
Minimizing the overall set-up uncertainties
to < 1 mm
De Ornelas, Mariluz, et al. "Assessment of intra-fraction motion during automated linac-based
SRS treatment delivery with an open face mask system."Physica medica92 (2021): 69-74.

18. Conclusions
•SGRT showed smallest deviations at the zero-couch angle and large ones with
couch kicks
•As non-zero angles were treated, couch walkouts contributed to SGRT signals
•By decomposing the SGRT signal and subtracting the systematic couch walkout
allows more accurate patient intra-fractional motion.

19. Perspectives
•More accurate tracking from hardware improvement (zoom in, CMOS etc) and
software specifically for SRS motion tracking
•Machine deviations should be considered in the presented signal, considering the
capability of knowing decomposed machine parameters at sub-mm precision
•Real time monitoring and estimation of multi-mets should be provided considering
the translational and rotational shifts and the distance to isocenter

20. Acknowledgements
Maria De La Luz De Ornelas, Ph.D., Co-PI
Nesrin Dogan, Ph.D.
Eric Mellon, M.D., Ph.D.
Beatriz Guevara, M.S.
William Amestoy, RT(T), CMD

21. University of Miami
Sylvester Comprehensive Cancer Center