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 â€œ100% prescription dose covers 95% of PTVâ€?. Then the 100% isodose volume was converted into a structure (100%IDV). At any radial angle Î¸ from contour geometry center in each axial slice, the radius of PTV is defined as R1(Î¸) and radius of 100%IDV is defined as R2(Î¸). The distance D(Î¸) is equal to the difference between R2(Î¸) and R1(Î¸). Then a new PTV radius is calculated by subtracting D(Î¸) from R1(Î¸). 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 Â± 0.08 to 0.88 Â± 0.05. GI increased by 1% on average from 4.09 Â± 0.9 to 4.10 Â± 0.95. Average V12Gy didnâ€™t change. If both original and modified plan were renormalized to 99% PTV coverage, PCI improved by 16% on average from 0.71 Â± 0.09 to 0.82 Â± 0.06, but GI decreased by 1% from 4.46 Â± 1.05 to 4.37 Â± 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.