Program Information
Tomotherapy Motion Compensation with Jaw and MLC
J Smilowitz1*, J Bayouth2 , E Chao3 , (1) University of Wisconsin, Madison, WI, (2) University of Wisconsin, Madison, WI, (3) Accuray Incorporated, Madison, WI
Presentations
SU-K-605-4 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 605
Purpose: Motion mitigation using jaws and MLC during helical TomoTherapy delivery is investigated. Dose distributions were generated to address three questions: the effect of motion on intended plan created with an ITV, the effect of motion mitigation using jaw and MLC compensation, and the impact of smaller PTVs based on GTV expansion only.
Methods: Treatment plans were created for eleven subjects (4 liver, 4 lung, 3 pancreas) accrued to an IRB approved study. Center of mass (COM) motion of the GTV was computed from 4DCT using sequential deformable propagation. Maximum inspiratory breath hold images were used to create an ITV. For each subject plans were generated with PTVs of 3mm expansion of both ITV and GTV. Patient specific target COM motion was combined with their optical guidance trace to establish a motion trace for the treatment length. The avg/min/max COM motion (cm) was lateral 0.8/0.1/1.4, ant/post 1.2/0.2/2.8, and sup/inf 1.9/0.8/3.5. Anticipated dose distributions were computed with a treatment delivery simulation tool assuming (1) no motion, (2) respiratory motion, and (3) respiratory motion compensated by adjusting the jaw and MLC positions during delivery.
Results: Intrafraction motion produced dose differences greater than ±10% of the prescribed dose when compared to no motion plans for all subjects (avg. volumes: overdose 180.2cc, underdose 136.4cc). Motion compensation decreased the average dose difference below ±5% in all but one case, due to a large DC offset in target position. Motion compensation directly on the GTV-based PTV (no ITV) reduced >10% overdosed volumes and had small volumes with dose differences > ±5% (19.1 and 4.4cc).
Conclusion: Tumor motion during TomoTherapy helical delivery produced plans with large volumes of tissue having substantial dose difference from planned dose. These differences were mitigated within clinically acceptable tolerances using MLC and jaw motion compensation, enabling further gain through margin reduction.
Funding Support, Disclosures, and Conflict of Interest: This work is funded in part by a University of Wisconsin and Accuray Research agreement.
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