Gamma Knife Dose Calculations Based On Monte Carlo Studies

The paper's object of study is the LunaTM-260whole body gamma knife treatm ent machine. Luna has developed by China and has been used in clinical.The pape r studyed the dosimetric properties of the Gamma Knife single-source and multi-so urces static focus. Purpose to setup the Gamma Knife Luna Monte Carlo dose cal culation model, and simulationly caclulate Gamma Knife dosimetry parameters. To solve the problem that the Luna Gamma Knife in the clinical use of single-source percentage depth dose (PDD), tissue maximum dose ratio (TMR), beam off-axis r atio (OAR), and dosimetric parameters such as output factors can not be measured. Compared Monte Carlo calculation resluts and treatment planning system data to verify the dose accuracy of Gamma Knife treatment for patients..Works involved the Gamma Knife head of geometric modeling and experimenta1measurements of film dosimeter and Monte Carlo simulation program. This paper introduces and discusses the Gamma Knife planning system for dose calculation model and their the advantage and disadvantage and the basic principle of the Mo nte Carlo method. Focus on the TMR-OAR dose calculation model use for the L una Gamma Knife planning system, and the feasibility and practicality of the Mon te Carlo code of MCNP4C for carrying out this study are discussed. Details the basic structure of the gamma knife-based Luna, the structure and size of the head section, the various parts of the material and radioactive sources, structure, shape MCNP dose calculation model of the modeling process. With the measurement dat a to verify the correctness of the calculation model, make sure built a computation al model correctly, the dosimetric parameters of the Gamma Knife single-source an d multi-source simulation and measurement data which is getted by Gafchromic E BT2new film dosimetry..Methods:Based on the Gamma Knife dose calculation model, I calculated dose parameters of the single-source and multi-source for all beam collimators in the30cm×30cm×30cm water phantom and the dose distribution the in the diamete r of16cm Gamma Knife dedicated plexiglass ball. Results:Percentage depth dose and off-axis are calculated for luna Gamma Kni fe6collimators (4mm×4mm,8mm×8mm,14mm×14mm,14mm×20mm,14mm x40mm,14mm x60mm) single-source and multi-source0.5cm,5cm an d10cm depth of the source in the water phantom and dose distribution curve in t he special ball modle. In0.5cm depth of the phantom, calculation results of the N o.4,No.5,No.6collimator of beam off-axis are not good; calculation results are g ood in5cm and10cm of the phantom. TMR(Tissue Maximum Ratio) value are c alculated from the PDD(percentage depth dose) according to the relationship betw een the PDD and the TMR. For single-source TMR calculation results, the raw da ta (measurements) in the planning system and the standard curve are compared, th e calculation results are well consistent with the standard curve, and There is a certain error between the calculation results and TPS data (measurement), which is less than5%. For the No.l collimator calculated values are more than the measur ed value from0to5cm depth in the modle, from5cm to15cm depth,the calcul ated values and measured values are basically the same, More than15cm depth,cal culated values are less than the measured values; For5the rest the collimators cal culate the values are consistent with the measured values, the measured value is g reater than the calculated value, an error is about2%-5%. In5cm depth square p hantom, beam off-axis comparison results of the Single-source:the data within the radiation field is good, but the data is not good outside the field. Each collimat or whichever is the focus at the dose as a standard value, the collimator on the N o.6most standard normalized calculated6collimator output factor and its comparis on with the measurement results. For the No.1collimator (greater than10%), and the rest were less than3%.Conclusion:Monte Carlo calculation model is well validated single-source beam percentage depth dose (PDD), the maximum dose ratio (TMR), the beam off-axis r atio (OAR) and output factor. Calculationthe results accord with measurement resul ts within the error range (5%) and the focus specialty of multi-source dose distrib ution was studied, the luna Gamma Knife dose distribution is presented. The result s show that the the luna Gamma Knife Monte Carlo dose calculation model can b e used for the validation of dosimetric parameters which has been founded. It ver y well soleved the problem that a single-source dosimetric parameters can not be measured.,while It can guide the Gamma Knife clinical plan design and dose calcu lation.This work laid the foundation for the Gamma Knife in the future research w ork...