(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: To evaluate and compare the treatment plan quality and delivery efficiency of VMAT plans using different location and number of beam isocenter for multiple brain metastatic from lung carcinoma after the whole bain radiotherapy.
Methods: 25 cases of brain metastasis from lung carcinoma with intracranial lesions<=3 were treated with 3DCRT of whole brain total dosage was 30Gy-40Gy, then for the late course metastatic targets were boosted to 56-60 Gy by VMAT. The original VMAT plans which were optimized under the single isocenter were recomputed by multi-isocenters which each arc underwent one isocenter of each lesions. The original VMAT plans consisted two coplanar arcs, while the recomputed plans under 2 to 3 isocenters consisited 2 to 3 coplanar arcs separately. Homogeneity index, heterogeneity index, dose coverage of targets and DVH statistics of PTV and OAR were calculated and compared for the two groups of the boosted VMAT course along with total number of monitor units and delivery efficiency.
Results: Paired comparison results of dose distributions indicated that multi-isocenter VMAT plans were significantly superior to single isocenter plans in lenses, optic nerves, brain stem and middle-ears. Especially for the cases that lesion located near by the stem, multi-isocenter plan reduced the stem dose about 1000cGy compared to the single-isocenter plans. However, there were not such trend in middle ears and spinal cord. As for targets there were no clinically significant difference in HI, CI and other PTV dose coverage. In terms of delivery efficiency, single-isocenter VMAT plans delivered on average took about 2.6 mins to multi-isocenter plans which need 3.1 to 4.7 mins according to the number of lesions.
Conclusion: Multi-isocenter VMAT is a feasible and practical method to significantly protect some OARs with quality target coverage for brain metastatic neoplasm of 2-3 lesions, while compromise a little planning efficiency.
Keywords
Not Applicable / None Entered.
Taxonomy
TH- External beam- photons: treatment planning/virtual clinical studies
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