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  5. Evaluation of An In-House Respiratory Tracking System for Phase Binning of Elekta Machine Log-File Control Points

Evaluation of An In-House Respiratory Tracking System for Phase Binning of Elekta Machine Log-File Control Points

A McGuffey1*, J Sick1,2 , (1) Louisiana State University, Baton Rouge, LA, (2) Mary Bird Perkins Cancer Center, Baton Rouge, LA

Presentations

(Sunday, 7/14/2019) 4:30 PM - 5:00 PM

Room: Exhibit Hall | Forum 5

Purpose: Evaluate the accuracy of an in-house respiratory tracking system for phase-binning of Elekta machine log file control points.

Methods: A programmable respiratory phantom was set to produce sinusoidal motion with 2 cm amplitude and 6 second period. The phantom was scanned using 4D-CT and motion was tracked using the Varian RPM system. Next, a sample lung SBRT plan was delivered using an Elekta Versa HD linear accelerator to the phantom under the same motion, which was tracked using the in-house system. Then, the binary machine log file for each beam was acquired and interpreted using a Python script. The respiratory trace from treatment and the RPM trace recorded during 4D-CT were compared using the Pearson correlation coefficient. To validate the phase calculation algorithm, phase was calculated for the in-house data and overlaid with the phase calculated by the reference RPM system. Control points were then binned according to phase using timestamps from the machine log file and respiratory trace.

Results: The Pearson correlation coefficient between the in-house and RPM traces was found to be 0.990 with a p-value of <0.001, indicating that the in-house system is consistent with the clinical RPM system. The calculated phases for the in-house trace were found to closely match the logged RPM phases via visual overlay. Time-correlation of log-file data to breathing phase was found to be feasible using the in-house system.

Conclusion: The in-house respiratory tracking system was validated for use in determining breathing phase during treatment by comparison with a clinical system. In addition, we show the feasibility of intra-fraction respiratory-correlation of machine log file data using an Elekta linear accelerator and an inexpensive, in-house tracking system. The in-house system validated in this study will be used to develop an intra-fraction log-file based assessment of dose delivery errors during lung SBRT.

Funding Support, Disclosures, and Conflict of Interest: Mary Bird Perkins Cancer Center Foundation

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