Purpose: To evaluate surface guided radiation therapy (SGRT) as an alternative to traditional laser and light field based alignment for prone breast patient set-up.
Methods: An IRB-approved retrospective analysis was conducted on 20 early-stage breast cancer patients treated at our institution in the prone position. 10 patients were initially set up using SGRT (VisionRT, London, UK) over a region of interest covering the patient’s back and ipsilateral chest wall. The SGRT setup was then verified by evaluating the alignment of skin markings with the room lasers and a diamond-shaped light field projected by the linac. The other 10 patients were set up using the room lasers and light field alone. In both groups, the set-up was verified using kV or MV imaging with soft-tissue and chest wall based alignment. The set-up times and couch shifts applied after IGRT were extracted from each patient’s treatment records. The two-tailed student t-tests were performed on the set-up times and couch shift magnitudes to compare SGRT with traditional alignment methods.
Results: Average set-up time (11m:59s vs. 10m:09s, p=.07) and couch shifts (0.88cm vs. 0.94cm, p=.69) were similar between the SRGT and control group, respectively. The modest increase in set-up time in the SGRT cohort is attributed to the additional time spent verifying the patient set-up position with the room lasers and light field after SGRT.
Conclusion: The results of this study demonstrate that SGRT can be used for prone breast setup instead of traditional laser or light field based alignment. The therapists showed preference to the SGRT system as it simplified patient set-up by providing automatic translational and rotational shifts (especially patient roll) over a large reference surface compared to manually estimating the set-up corrections with light field alignments.
Breast, Image-guided Therapy, Surface Matching
TH- External Beam- Photons: onboard imaging (development and applications)