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Influences of Optimization Grid Size to Leaf Open Time Histogram in NSCLS SBRT Using Helical Tomotherapy

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J Gu

J Gu1*, (1) Shandong Cancer Hospital Affiliated to Shandong University, Jinan, Shandong


SU-I-GPD-T-607 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To investigate the effect of plan optimization grid size on helical tomotherapy leaf open time histogram for lung Stereotactic Body Radiation Therapy.

Methods: Five patients of Non-Small Cell Lung Cancer were enrolled. For each patient, three plans with different dose optimization grid size (fine, normal, coarse )were created by Helical Tomotherapy Planning Station(version:5.0,GPU Acceleration and VoLo). The plan monitor units (MUs) and the leaf open histogram were compared. Paire-Wilcoxon test was used in statistical sanyasis.

Results: The Mus and leaf open histogram have significant difference from various optimizations grid sizes. The monitor units of fine (9966.17MU) is 3.013% (10266.44MU, p=0.006) and 7.7235% (10737.80MU, p=0.018) lower than normal and coarse. The maximum of leaf open time (Timemax) was accompanying grid size increase. Timemax of fine, normal, coarse optimization grid size is 531ms, 547ms, 581ms, respectively. The total percent of short open time(15-100ms) of fine(5.894±2.2905%) is higher4.988%(p=0.033) than normal(5.690±1.412%) ,have no difference to coarse(5.960±1.161%). But the total percent significant impact on total percent of open time 101-300ms, 301-500ms and exceeds 500ms. The total percent of open time 101-300ms of fine, normal, coarse is 26.193±11.482%,28.229±11.653%,32.525±11.081% and 301ms-500ms is 41.586±17.170%,40.908±16.230%,24.444±8.045%. The exceed 500ms is 22.960±23.479%,22.237±22.904%,33.516±14.750%.

Conclusion: In NSCLC helical tomotherapy SBRT planning, the smaller optimization grid size need less Mus than lager size but it will create more percent of leaf short open time. Considering that, the physicist should choose the suitable pitch and modulation factor to reduce percent of leaf short open time.

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