| Dose Profiles for a Single Shot of Gamma Knife : Leksell GammaPlan versus Modified Variable Ellipsoidal Modeling Technique |
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Beong Ik Hur, Byung Gwan Choi, Dong Wan Kang, Won Ho Cho, Seung Heon Cha, Chang Hwa Choi |
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Department of Neurosurgery, Pusan National University Hospital, Pusan National University School of Medicine, Busan, Korea |
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| Abstract |
Purpose
A high degree of precision and accuracy in Gamma Knife Radiosurgery (GKRS) is a fundamental requirement for the
therapeutical success. Elaborate radiation delivery and dose gradients with the steep fall-off of radiation are clinically applied thus
necessitating a dedicated quality assurance (QA) program in order to guarantee the dosimetric, geometric accuracy and reduce
all the risk factors that can occur in GKRS. In this study, as a part of QA we tested precision of beam alignment through two
theoretical approaches : Leksell GammPlan (LGP), modified Variable Ellipsoidal Modeling Technique (VEMT). From this comparative analysis, precision of Gamma Knife Radiosurgery is confirmed. so the clinical application is finally performed based on precision and accuracy of GKRS like this.
Materials and Methods : Precision is determined by comparing evaluated dose profiles of the resulting dose distribution located in a target surrounding the focus point (x=100mm, y=100mm, z=100mm) with the dose profiles calculated by VEMT, assuming identical geometrical and radiophysical conditions. Specifically the width at the 50% isodose level, that is, full-width-of-halfmaximum (FWHM) was tested under such conditions that a patient’s head is simulated as a sphere with a diameter of 160mm.
Results
Two theoretical approaches produced almost the similar outputs. All theoretical dose profiles along x-, y-, and z- axes
calculated through VEMT method agreed with LGP’s dose profiles within specifications (1mm at 50% isodose level) except for a
little difference of dose profiles along z axis for 14mm and 18mm collimators in a high isodose level.
Conclusion
The independent verification method for the results of LGP’s dose planning we developed assure clinically the perfect treatment for GKRS’ patients. This approach can verify the data of dosimetry and physics calculated through LGP. In addition,
we can work to confirm the validity of dose distributions for all the collimators determined through the regular preventative maintenance program using the modified VEMT. We think the newly developed method, modified VEMT, is very effective as a part of
QA and need to come into wide use at many Gamma Knife -centers. |
| Key Words:
Gamma Knife radiosurgery, Leksell GammPlan, Modified variable ellipsoidal modeling technique. |
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