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Dose Recomputation Versus Dose Deformation for Stereotactic Body Radiation Therapy in Lung Tumors: A Dosimetric Study

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M Ma

M Ma1*, J Bayouth2 , R Flynn1 , J Xia1 , (1) niversity of Iowa Hospitals and Clinics, Iowa City, IA, (2) University of Wisconsin, Madison, WI


SU-E-J-260 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate the dosimetric accuracy between recomputed dose and deformed dose for stereotactic body radiation therapy in lung tumors.

Methods: Two non-small-cell lung cancer patients were analyzed in this study, both of whom underwent 4D-CT and breath-hold CT imaging. Treatment planning was performed using the breath-hold CT images for the dose calculation and the 4D-CT images for determining internal target volumes. 4D-CT images were reconstructed with ten breathing amplitude for each patient. Maximum tumor motion was 13 mm for patient 1, and 7 mm for patient 2. The delivered dose was calculated using the 4D-CT images and using the same planning parameters as for the breath-hold CT. The deformed dose was computed by deforming the planning dose using the deformable image registration between each binned CT and the breath-hold CT.

Results: For patient 1, the difference between recomputed dose and deformed mean lung dose (MLD) ranged from 11.3%(0.5 Gy) to 1.1%(0.06 Gy), mean tumor dose (MTD) ranged from 0.4%(0.19 Gy) to -1.3%(-0.6 Gy), lung V20 ranged from +0.74% to -0.33%. The differences in all three dosimetric criteria remain relatively invariant to target motion. For patient 2, V20 ranged from +0.42% to -2.41%, MLD ranged from -0.2%(-0.05 Gy) to -10.4%(-2.12 Gy), and MTD ranged from -0.5%(-0.31 Gy) to -5.3%(-3.24 Gy). The difference between recomputed dose and deformed dose shows strong correlation with tumor motion in all three dosimetric measurements.

Conclusion: The correlation between dosimetric criteria and tumor motion is patient-specific, depending on the tumor locations, motion pattern, and deformable image registration accuracy. Deformed dose can be a good approximation for recalculated dose when tumor motion is small.

Funding Support, Disclosures, and Conflict of Interest: This research is supported by Siemens Medical Solutions USA, Inc and Iowa Center for Research By Undergraduates

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