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"Cleaning" the Dose Spill in Lung SBRT Plans

G Narayanasamy1*, D Desai2 , M Bimali3 , E Galhardo1 , H ElAsmar 2 , J Penagaricano1 , S Maraboyina1 , L Peacock1 , T Kim1 ,F Xia1 ,E Johnson4 , S Morrill1 , (1) Department of Radiation Oncology, University of Arkansas for Medical Sciences, Little Rock, AR, (2) Memorial Hospital, Hixson, TN, (3) Department of BioStatistics, University of Arkansas for Medical Sciences, Little Rock, AR (4) University of Kentucky Medical Ctr, Lexington, KY


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To identify and investigate planning techniques that can possibly reduce low-to-intermediate dose spillage (measured by R50%, and D2cm values) in lung SBRT plans.

Methods: Dose fall-off outside the target was studied in 102 SBRT VMAT plans of lung tumor. Plans having R50%, or D2cm higher than RTOG 0915, 0813 recommended tolerances were re-planned with two new optimization constraints. Deviation in D2cm can be satisfied using dose optimization constraint to a uniform 2 cm wide ring outside PTV. R50% dose constraint required creation of a ring (OptiForR50) extending 5 cm axially and 1 cm longitudinally outside PTV. Wilcoxon signed-rank test was performed to compare changes in R50% and D2cm of target, V20 to normal lungs and doses to OARs.

Results: In 102 lung SBRT plans with PTV sizes ranging from 5 to 179 cc, 32 plans with minor deviations in R50% or D2cm were re-optimized. Reductions of 4.3±4.8% and 0.8±0.4% (p-values < 0.05) were observed in the mean values of R50% and D2cm, respectively. V20 of normal lungs, mean dose to heart and aorta were significantly lowered.

Conclusion: Placing additional dose constraints on two new contours led to lower dose spillage in lung SBRT plans. All the re-optimized plans passed the RTOG-0915 criteria with no deviation.


Stereotactic Radiosurgery, Dosimetry


Not Applicable / None Entered.

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