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Dosimetry Comparison of VMAT SRS Plans for Multiple Lesions

D Zhu1*, Z Huang2 , C Lu3 , W Liu4 , (1) Saint Thomas Rutherford Hospital, Murfreesboro, TN, (2) Saint Thomas Hospital, Brentwood, TN, (3) ,Frisco, TX, (4) Yale Univ. School of Medicine, New Haven, CT


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To study the dosimetry differences of three VMAT SRS plans for treating three brain lesions; one plan covers all three lesions; one plan covers two of the three lesions; and the last plan covers the 3rd lesion.

Methods: The three lesions were right occipital/cerebellar/temporal lesions, respectively. Prescription dose (Rx) was 20 Gy. AcurosXB_11031 with 1 mm calculation grid size used. Three VMAT plans were developed with plan 1 covering all 3 lesions, plan 2 covering right cerebellar and right temporal lesion, and plan 3 covering right occipital lesion. Each plan used 3 partial arcs and 100% of Rx covered 97% of PTV. The PTV volume of the three lesions was 6.34 cc and diameter was 2.3cm; the PTV volume of right cerebellar and right temporal lesions was 2.46 cc and diameter was 1.7cm; the PTV volume of right occipital lesion was 3.93 cc and diameter was 2.0cm. At frontal view, the distance between right cerebellar and right temporal lesions was about 3.5cm. At beam eye view, the distance between right cerebellar and right occipital lesions at gantry 330 degree was about 6.8cm.

Results: In the three plans, the conformity indexes (CI) are 1.114, 1.017, and 1.020, respectively; target coverage QA (Q) are 85.3%, 91.0%, and 85.1%, respectively; the homogeneity indexes (HI) are 131.9%, 120.1%, and 132.4%, respectively; the V12Gy of normal brain are 14.55 cc, 6.34 cc, and 7.90 cc, respectively; the ratio of diameter of 50% isodose to the diameter of PTV are 1.70, 1.71, and 1.50, respectively; each lesion’s min/max/mean doses are comparable; VMAT QAs passed; critical structures’ doses were comparable and within tolerance.

Conclusion: Based on the distance between lesions, dose planner can optimize VMAT SRS treatment plan to reduce the treatment time and achieve normal brain’s V12Gy<10cc.


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