因為加馬刀只有四種圓形的錐筒照野，所以當碰到不規則的病炤時，往往圓形照野很難模擬不規則病炤的最佳分佈，意即使用大小不同的圓形照野去完整涵蓋形狀不規則的區域往往不是有劑量過高的高劑量區出現，要不然就是劑量過低的低劑量區域的出現；所以如何選用有限的圓形照野及搭配治療中心點的選取以便組合出劑量分佈的最佳化便是本研究的主要目的。本實驗是選用加馬刀專屬的治療計劃系統，Gamma Plan 及幾何中心點的方法運用治療計劃的試算讓4 個大小不同的圓形照野4mm、8mm、14mm、18mm 有效的分佈到假想的不規則病炤上，再以含蓋指數(Covering Number, CN)評定治療中心點選擇的最佳化。本實驗發現無論多複雜病炤，在幾何中心截面上，一定可以找到一組主要的質量中心點，以此質量中心點劃出一個最適當的圓，此圓的直徑便是本實驗治療圓錐的大小，如果離開此主要質量集中區後還有另一組或多組質量集中區再分段去找出質量區由大到小的質量中心點再一一去做照野中心點的配置就可以找出最佳的照射中心點；它們的順形參數(Conformity Number)最大可以達到0.81，最小是0.1735。

Gamma Knife radiosurgery could deliver radiation dose precisely to the lesion and with a compatible lower dose if every shot located correctly. The purpose of this study is to determine the adequate shot location by geomatric mathematic method in GammaPlan planning. Different lesion length and volumn are investigated by setting different cone size and with the 50% dose curve as a coverage indication to the lesion edge to determinate the first shot location. By abutting the second and the first cone 50% dose curve and with the coverage to the lesion edge as the indicaton to asign the second shot location. Follow the simple rule for the more next shots if needed to determinate the adequate isocenters location. The 201 sources toward to the isocenter formed a uniform iso-volumn center. And with geomatric view point to set the mutli-shot location lead to a sufficient shots therefore decrease the hot dosage compared to random superimporsed overlapping by different cones. The determination of adequate radiosurgery shot location in geomatric mathematic method in GammaPlan decrease the hot dose and escalate three to five percent isodose curves of dose coverage.