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Improved Dosimetric Accuracy Using An Innovative Phased Weighted Density Scheme for Stereotactic Lung Radiotherapy

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D Mohatt

D Mohatt1,2*, H Malhotra1,2, 1. Department of Physiology and Biophysics, State University of New York at Buffalo 2. Department of Radiation Medicine, Roswell Park Cancer Institute


SU-I-GPD-T-519 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The target volume for stereotactic lung radiotherapy is preferentially defined by the composite of 10 gross tumor volumes (GTVs) over the course of single respiratory period. However, dose computation is always preformed using a single static CT image set. This investigation explores the validity of using a novel phased weighted density structure for more accurate dose computation.

Methods: A Quasar respiratory motion phantom was used to simulated lung tumor motion. 4DCT imaging was employed to generate free breathing (FB), average (AIP), and maximum intensity projection (MIP) image sets. A standard internal target volume (ITV) was created from the delineation of 10 individual GTV phased structures. In addition, we created a phase weighted density (PWD) structure via overriding the CT values to the super imposed GTV overlapping regions. Each plan with unique FB, AIP, MIP and PWD CT image set was calculated using both the Anisotropic Analytical Algorithm (AAA) and Acuros XB (AXB). Metrics for evaluation were performed in accordance to ICRU report number 83.

Results: The dose differential between AXB versus AAA was minimal for the PWD scheme with ΔD₂ = 1.4 ± 0.4%. Similarly, MIP ΔD₂ = 2.7 ± 0.1%, AIP ΔD₂ = 3.1 ± 0.4%, and FB method with ΔD₂ = 3.3 ± 0.3%. In addition, we observed a corresponding change in the target homogeneity index where ΔHI_FB = 8.6 ± 0.5%, ΔHI_AIP = 3.9 ± 0.4%, ΔHI_MIP = 2.5 ± 0.4%, and ΔHI_PWD = 0.7 ± 0.6%.

Conclusion: With improved computational performance in heterogeneous low density media, the AXB algorithm when compared with AAA generated more analogous results using the phase weighted density image set. The inaccurate representation associated with the relatively low density FB image computation when compared to AIP, MIP and PWD resulted in greater dose discrepancy.

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