Room: Room 209
Purpose: To validate jaw-based motion mitigation during helical TomoTherapy delivery using a custom motion phantom setup.
Methods: Centroid GTV motions for six subjects accrued to an IRB approved study were computed from 4DCT using sequential deformable propagation at each phase. Dynamic jaw helical TomoTherapy plans with 3mm margins were generated (P0). PTV sizes and S/I motion ranges were 5.6-190.7cc and 3.8-12.3mm. Motion traces were used to modify the jaw files to generate S/I motion compensated plans (P1.) The anticipated dose distributions were computed with a treatment delivery simulation tool in static (M0) and moving conditions (M1). P0 and P1 dose was recomputed for QA plans on the Accuray "cheese" phantom. The P0 plan was delivered to a static phantom (P0M0). To deliver the modified plan to a moving phantom (P1M1), a custom stage was constructed and attached to a Computerized Imaging Reference Systems, Inc. motor. The motion and treatment were synced by triggering the play button for phantom motion with the radiation "on" state.
Results: Gamma analysis (2%/2mm, 20% threshold) between P0M0 and P1M1 computed and measured film doses exceed 98% and 88% respectively. Within the high dose/low gradient region only, the pass rate exceeds 99%. Failures occur at the S/I field edges. FWHM of measured dose profiles through the PTV center for P0M0 and P1M1 plans agreed with an average of 0.0 mm (SD 0.8.)
Conclusion: Validation of motion compensated plans and the system's ability to deliver the plans under dynamic conditions are important for novel motion management techniques. Excellent agreement between P0M0 and P1M1 computed doses validate the generation of comparable plans. Measured dose distributions agreed well and support the system's ability to execute the P1 plans in a moving phantom and deliver excepted dose inside and outside of PTV region, with minimal disagreement at the field edges.
Funding Support, Disclosures, and Conflict of Interest: This work is partially supported by a University of WI/Accuray research collaboration.