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An Auto-Modified PTV Method to Improve Conformity for Single Isocenter Multiple Lesions SRS Conformal Dynamic Arc Plans

L Fu*, H Liu , Y Yu , Thomas Jefferson University, Philadelphia, PA


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To implement the auto-modified planning target volume method for single isocenter multiple lesions stereotactic radiosurgery dynamic arc plans. The dosimetry results are to be evaluated.

Methods: Ten brain SRS patients (among them seven patients have two lesions and three patients have three lesions), were randomly selected. Plans were created using 4-8 non-coplanar dynamic arcs in Eclipse. For each case, an original plan was generated by fitting multi-leaf collimator (MLC) to the combined PTV and normalized to “100% prescription dose covers 95% of PTV�. Then the 100% isodose volume was converted into a structure (100%IDV). At any radial angle θ from contour geometry center in each axial slice, the radius of PTV is defined as R1(θ) and radius of 100%IDV is defined as R2(θ). The distance D(θ) is equal to the difference between R2(θ) and R1(θ). Then a new PTV radius is calculated by subtracting D(θ) from R1(θ). Based on this algorithm, A MATLAB code has been developed to automatically generate the modified PTV contour, and a new plan was created by fitting the MLC to the auto-modified PTV. Paddick conformity index (PCI), gradient index (GI) and V12Gy were compared for total 23 lesions between the original and the modified plans.

Results: PCI increased by 12% on average from 0.79 ± 0.08 to 0.88 ± 0.05. GI increased by 1% on average from 4.09 ± 0.9 to 4.10 ± 0.95. Average V12Gy didn’t change. If both original and modified plan were renormalized to 99% PTV coverage, PCI improved by 16% on average from 0.71 ± 0.09 to 0.82 ± 0.06, but GI decreased by 1% from 4.46 ± 1.05 to 4.37 ± 1.09. Average V12Gy decreased 3%.

Conclusion: The auto-modified PTV method is simple and effective to improve the conformity of single isocenter multiple lesions SRS conformal dynamic arc plans.


Stereotactic Radiosurgery, Brain, Treatment Planning


TH- External beam- photons: treatment planning/virtual clinical studies

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