Dosimetric Phantom Consistency of TMR-10 Protocol in Homogeneous and Inhomogeneous Regions in Gamma Knife Radiosurgery Planning

INTRODUCTION: The algorithms used in the GammaPlan treatment planning system are “Tissue Maximum Ratio (TMR) classical,” “TMR 10,” and “convolution” algorithms, respectively. In this study, the consistency of dosimetric measurements with the TMR 10 protocol used in SRC (stereotactic radiosurgery) planning in lesions located in homogeneous and inhomogeneous regions in different intracranial location scenarios was investigated.
METHODS: n this study, the accuracy of administration of multiple metastasis treatment on the Gamma Knife Perfexion device was investigated. Computed tomography was performed with 1 mm cross-section intervals of CIRS brand Atom randofantoma. Critical organs and three different brain metastases located in homogeneous and heterogeneous regions, which are not on the same plane with each other, were drawn on the phantom. Planned target volume (PTV) volumes were created without margining the drawn gross tumor volumes, and three separate plans were made for three different PTV volumes. All plans were calculated using the TMR 10 algorithm. Critical organ doses were kept below the brain-SRC criteria for all calculated plans. Gafchromic EBT-3 film was placed on the sections with the target volume drawn on the phantoms and irradiated (1600 cGy, 50% isodose area). Measurements were made three times. The measured film results and the doses calculated from the planning were compared with gamma index analysis for different tolerance values.
RESULTS: In our study, for three different lesions planned and irradiated with different gradient index values, a difference of 2.11–9.58% was observed between the values calculated with the TMR-10 protocol and the values obtained in the dosimetric measurement. A decrease in consistency was observed, especially in inhomogeneous region placements.
DISCUSSION AND CONCLUSION: There may be inconsistency between the TMR-10 protocol and actual dosimetric measurements, especially around inhomogeneous intracranial structures. We hope that this inconsistency will decrease in the future with the developing dose calculation protocols.