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Commissioning, Performance and QA Tests for Real-Time Motion Tracking and Correction with MLC and Jaws

G Chen*, A Tai, S Lim, T Keiper, X Li, Medical College of Wisconsin, Milwaukee, WI

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To evaluate the performance and establish a QA process for a real-time motion tracking and correction (RMTC) system using MLC and jaws in helical tomotherapy delivery (HTD).

Methods: A RMTC system, utilizing a 90°-offset-mounted 2D kV x-ray imaging component to monitor either implanted fiducials or lung tumor, together with external surrogates to instruct binary MLC and jaws for motion correction during HTD, was recently installed in our institution. The kV imaging dose was measured with a pencil chamber and CTDI phantoms. Tracking plans were generated on fiducials or high-contrast-block embedded 3D phantoms and delivered with them placed on certain motion platforms driven by various motion traces. Tracking geometry accuracy was obtained by evaluating the difference between the predicted and instructed target positions. Ion chamber (1D) and film (2D) measurements with motion correction were compared to those with no correction or no motion at all. The measured dose using 3D dosimeters, and delivered dose reconstructed on daily MVCT images, were compared with the planned dose. Patient plans were applied on 3D phantoms and delivered with closely resembling patient specific motion patterns.

Results: The typical imaging dose was <1 cGy. The tracking geometry accuracies were within 1.5 mm. Dose constancy with 1D measurements was within 2% for typical motion but could be 3-6% with extreme large motion (4 cm). 2D measurements indicated that motion tracking did rectify the motion effect. Gamma passing rates for 3D dose measurements, with 3%, 2 mm and 10% threshold criteria, were >85% and >95% for non-respiratory and respiratory tracking, respectively. Mean doses to PTV and organs-at-risk for reconstructed doses on MVCT were within 1% of planned doses.

Conclusion: Performance of the first clinical RMTC system for HTD is within specifications. A machine and patient QA process was established for patient treatments using the RMTC system.

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Funding Support, Disclosures, and Conflict of Interest: We thank Accuray Inc. for their technical and financial supports.

Keywords

Not Applicable / None Entered.

Taxonomy

TH- External Beam- Photons: Motion management - intrafraction

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