Abstract
One of treatment planning techniques with Leksell GammaPlan (LGP) for Gamma Knife stereotactic radiosurgery (GKSRS) uses multiple matrices with multiple dose prescriptions. Computational complexity increases when shots are placed in multiple matrices with different grid sizes. Hence, the experimental validation of LGP calculated dose distributions is needed for those cases. For the current study, we used BANG3 polymer gel contained in a head‐sized glass bottle to simulate the entire treatment process of GKSRS. A treatment plan with three 18 mm shots and one 8 mm shot in separate matrices was created with LGP. The prescribed maximum dose was 8 Gy to three shots and 16 Gy to one of the 18 mm shots. The 3D dose distribution recorded in the gel dosimeter was read using a Siemens 3T MRI scanner. The scanning parameters of a CPMG pulse sequence with 32 equidistant echoes were as follows: TR=7s, echo step = 13.6 ms, field‐of‐view = 256 mm× 256 mm, and pixel size=1 mm×1 mm. Interleaved acquisition mode was used to obtain 15 to 45 2‐mm‐thick slices. Using a calibration relationship between absorbed dose and the spin‐spin relaxation rate (R2), we converted R2 images to dose images. MATLAB‐based in‐house programs were used for R2 estimation and dose comparison. Gamma‐index analysis for the 3D data showed gamma values less than unity for 86% of the voxels. Through this study we accomplished the first application of polymer gel dosimetry for a true comparison between measured 3D dose distributions and LGP calculations for plans using multiple matrices for multiple targets.PACS number: 87.53.Ly, 87.55‐x, 87.56 ‐g
Highlights
134 Gopishankar et al: 3D BANG3 dosimetry of Gamma Knife for multiple matrices based plans using 3T magnetic resonance imaging (MRI) 134(4, 8, 14, and 18 mm beam diameters) can be used to treat targets of any shape
There are many studies on applications of the polymer gel dosimetry technique to Gamma Knife stereotactic radiosurgery (GKSRS).[2,3,4,5,6,7,8,9,10,11,12] most of these studies evaluated the 3D dose distributions computed by the Leksell GammaPlan treatment planning system (LGP) (Elekta Instrument AB, Stockholm, Sweden) for cases with single shot or multiple shots placed in one dose matrix
An important question is the validity of the multiple matrix method, in particular, with older versions of LGP, in terms of the dose prescription to multiple targets scattered over the multiple matrices
Summary
134 Gopishankar et al: 3D BANG3 dosimetry of Gamma Knife for multiple matrices based plans using 3T MRI 134(4, 8, 14, and 18 mm beam diameters) can be used to treat targets of any shape. There are many studies on applications of the polymer gel dosimetry technique to GKSRS.[2,3,4,5,6,7,8,9,10,11,12] most of these studies evaluated the 3D dose distributions computed by the Leksell GammaPlan treatment planning system (LGP) (Elekta Instrument AB, Stockholm, Sweden) for cases with single shot or multiple shots placed in one dose matrix. An important question is the validity of the multiple matrix method, in particular, with older versions of LGP, in terms of the dose prescription to multiple targets scattered over the multiple matrices To answer this question, Sandilos et al[9] recently used polymer gel dosimetry. The resulting dose matrix (named as global matrix) was used for comparison with measured dose distributions
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