Feasibility of X-Ray Acoustic Computed Tomography as a Tool for Noninvasive Volumetric In Vivo Dosimetry

motion XZ 6.3 (range: 5.9-7.1) mm, YZ 10.4 (9.6-11.2) mm, and ZZ 7.1 (6.6-7.7) mm. Root Mean Square (RMS) error between TT-tracked tumor motion and RPM was <0.9mm in all directions. Tumor B (4cm): TT could not track the position of the tumor at all angles as half-fan CBCT captured the tumor in only half of the images and high density and central airway structures obscured the target. Therefore, analysis was only performed for 100 (300-40 ) kV-source rotation. 4DCTmotion was XZ 1.8, YZ 7.5 and ZZ 8.6 mm. 100 TTon clinical kV projection series showed mean motion XZ 3.7 (2.5-5.8) mm, YZ 7.3 (5.3-9.2) mm, and ZZ 7.8 (5.5-10.6) mm. RMS error between TT and RPM was <1.1mm. Benchmarking tumor A: 360 TT showed mean motion X Z 3.5, Y Z 11.6 and Z Z 5.2 mm with standard deviation (SD) <0.7mm. Correlation coefficients of TT-tracked tumormotionwith center ofmass displacement on 4DCTwere 0.64, 0.95 and 0.84 (X, Y, Z). For tumor B: 2 sets of TT over 100 (300-40 /120-220 ) showed mean motion XZ 1.9, YZ 7.7 and ZZ 8.4mm (SD<0.8mm) and correlation coefficients of 0.63, 0.94 and 0.91 (X, Y, Z). Conclusions: TT software can track small lung tumors when they are visible in kV projections. Tumor motion during CBCT can vary from the planning 4DCT. TT and RPM motion were closely associated. Benchmarking TT against known tumor displacements showed good agreement. Author Disclosure: J.R. van Sornsen de Koste: I. Travel Expenses; has received travel support of Varian Medical Systems. M. Dahele: I. Travel Expenses; has received travel support/honoraria from Varian Medical Systems and travel support from Brainlab. S. Senan: I. Travel Expenses; has received travel support and honoraria from Varian Medical Systems. B. Slotman: I. Travel Expenses; has received travel support/honoraria from Varian Medical Systems. W. Verbakel: I. Travel Expenses; has received travel/honoraria support from Varian Medical Systems.