(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: To evaluate the feasibility and impact of motion management by implementing real time onboard kV imaging during DIBH lung SBRT.
Methods: A lung cancer patient with diaphragm adjacent tumor was treated using DIBH for lung and OAR sparing during SBRT. The 5 fraction SBRT plan used VMAT technique with two partial arcs and a PTV generated from a GTV+6mm margin from a DIBH simulation CT. Initial image-guidance was performed with DIBH and gated-CBCT. Real time onboard kV imaging triggered at initiation of each arc with subsequent 15 degree gantry rotation acquisition intervals. Treatment was gated using the Varian RPM system. The kV images were closely monitored by physicists and therapists as a supplementary motion monitoring system. Matched DRRs for kV images obtained at various gantry angles were generated in the treatment planning system and analyzed for variation based on anatomy land markers including the diaphragm/lung boundary.
Results: The patient received the treatment with no interruption other than normal breathing between breath hold. The GTV volume reduced from 3.6cc in the planning CT to 1.2cc as contoured in the CBCT acquired before the 5th fraction of SBRT. Diaphragm/lung boundary was captured at most imaging angles and the average distance from the baseline was 4mm (superior) with standard deviation of 3mm for all 10 arcs imaged over the course of treatment. A strong correlation (corr=0.81) was found between the RPM signal and the imaged diaphragm position. Superior diaphragm drift (0.037mm/degree) away from baseline during the treatment process was observed.
Conclusion: This work indicates the potential for implementing real time kVs to monitor the diaphragm position during DIBH treatment for lower lobe lung tumors. Quantitative analysis shows kV can be used in conjunction with other motion management systems to optimize the PTV margin, treatment length, and the triggering of the gating signal.
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