Inter-fractional Positioning Study for Breast Cancer with Proton Therapy using a 3D Surface Imaging System

Transcription

1 Inter-fractional Positioning Study for Breast Cancer with Proton Therapy using a 3D Surface Imaging System Li Zhao, PhD, DABR Procure Proton Therapy Center in Oklahoma City Abstract #: O63 PTCOG 53rd meeting, Shanghai, China, June 13, 2014

2 Acknowledgement Physicists: Dr. Yuanshui Zheng Dr. Jeff Gao Physicians: Dr. Gary Larson Dr. Nancy Cersonsky 2

3 AlignRT: A real-time 3D surface imaging (SI) system Introduction Data camera Procure Oklahoma City Inclined Beam line Room (Gantry 30 and 90) 3

4 Objective To study the performance of AlignRT 3-cameras realtime surface-based imaging system for daily breast alignment and tracking inter-fractional movements and anatomy in proton therapy To compare the absolute shift difference between setup with X-ray using fiducial markers and setup with the surface-based imaging system 4

5 Methods and Materials Patient Setup: Vac-lok, alpha cradle, breast board, index bar BB (nipple), wires (scar, drain site, and margins of chest wall) HFS, one arm above head, one arm down, head tilted. WBRT patient has implanted fiducial markers. Patient is pre-aligned using skin tattoos. VeriSuite X-ray system is used to align bony anatomy and implanted fiducials. Align-RT use to capture secondary surface images, but not for patient alignment. Daily 6 DOF robotic couch coordinates at each treatment position after IGRT were recorded to study the patient set up variations. 5

6 WBRT orthogonal kv X-ray images 6

7 Clinical Study Cases Relative Positioning Study A (Chest wall +SCV): Stage IIIA, left breast, triple positive, post mastectomy, 4 fields with 2 iso-centers (LAO & ASO, 2 match lines) 2 treatment couch positions (couch 0 and couch 270) Ref Image: 3D Reference surface image acquired on 1st Tx day Study B (Whole breast): Absolute Positioning Stage T1cNoMo, left breast, triple negative, post lumpectomy 2 treatment couch positions (couch 0 and couch 270) Ref Image: 3D Reference surface image generated from planning CT image 7

8 Surface Images Examples Chest Wall +SCV WBRT ASO Field 8

9 9

10 Study A: Relative positioning 10

11 Study A: Relative positioning 11

12 Study B: Absolute positioning 12

13 Translational Shifts Frequency Histogram Relative Positioning 60% Absolute Positioning 50% The majority of the agreement between SI shift and X-ray shift are within 2 mm. 13

14 Correlations between X-ray and SI system X ray calculated shifts = couch coordinates at Tx position - couch coordinates at setup position* VisionRT calculated shifts = VRT surface image at Tx position - VRT surface image at setup position *Setup position: patient is aligned with skin tattoos only. This is a prior X-ray alignment position. 14

15 Advantages of SI for Breast Cancer Non-invasive 3D surface imaging technology No radiation Dose Pre-position patient to reduce no. of X-ray images Compatible with existing IGRT interface Patient Surveillance: Monitor patient movement during Tx Monitor Respiration motion Patient Safety: Match SI directly to treatment plan minimizing positional errors Monitor couch shift for multi-isocenter Tx Verify patient positioning at couch angles where x-ray image is not possible 15

16 Challenges of SI for Breast Cancer Variation with ROI used for registration Low correlation with films Sensitive to deformation /difficult to interpret Large distance from camera to iso (FOV intensity) HD camera vs. standard camera Camera positions and camera FOV coverage 16

17 Summary SI has a potential to allow more accurate setup and enhance the safety of treatment delivery. Good correlations are found between SI and X-ray for the couch shifts between setup and Tx positions. The majority of the agreement between SI shift and X-ray shift are within 2 mm for the final Tx positions, however, SI still suggests small shifts after patient is aligned with X-ray by bony anatomy and markers. AlignRT translational and rotational shifts are sensitive to ROI selection. Rotational shifts are less reliable. Further studies are needed to better understand the correlations between X-ray system and AlignRT system. Motion management such as deep inspiration breath hold is under investigation. 17