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A Phantom Study to Determine the Dosimetric Effects of the Primary Image Choice Used for SBRT Radiotherapy Planning Following 4DCT Simulation

R Teboh Forbang*, B Lewis , A Ndlovu , Hackensack university Medical Center, Hackensack, NJ


(Wednesday, 8/1/2018) 10:30 AM - 11:00 AM

Room: Exhibit Hall | Forum 2

Purpose: 4DCT simulation is useful when planning for mobile tumor radiotherapy. This results in several primary image choices that may have dosimetric effects on the treatment plan. Our goal was to study these effects for the non-gated and gated radiotherapy deliveries.

Methods: The Quaser Motion Phantom with a lung tumor insert and Standard Imaging’s Exradin A16 inserted into the tumor was used for 4DCT simulation. The possible images for planning the non-gated delivery were (a) 3DCT, (b) Ave4DCT0%-90%, and (c) UntagRec, where UntagRec (Philips Brilliance Big Bore CT), is a 3D reconstruction of the acquired CT images. For the gated technique, we used a window 40%-60%, and considered 2 additional images, Ave4DCT40%-60% and 50% exhale. For the non-gated technique, we first planned on the Ave4DCT0%-90%, where we used a dose of 500cGy to the PTV. We copied all plan parameters to the other image sets and determined the planned dose to the ion chamber in each case. By delivering the treatment plan on the phantom, we measured the dose and compared with the planned dose in each of the scenarios. We repeated the process for the gated technique.

Results: For the non-gated technique, we observed 2.1%, 2.5%, and 3.1% as discrepancy between the measured and planned dose when the image sets 3DCT, UntagRec, and Ave4DCT0%-90% respectively, were used as primary. For the gated technique, we observed 0.7%, 0.5%, 1.2%, 0.8%, and 0.7% as discrepancy between measured and planned dose when the image sets 3DCT, UntagRec, Ave4DCT0%-90%, Ave4DCT40%-60%, and 50% exhale, respectively, were used as primary.

Conclusion: Our study shows that the dosimetric effects of the primary image choice does not exceed 1%. We only considered point dose within the target with no reference to dose to normal tissue. Future studies will include film that will characterize dose distribution in addition.


CT, Dosimetry, Stereotactic Radiosurgery



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