MAGAT gel and EBT2 film‐based dosimetry for evaluating source plugging‐based treatment plan in Gamma Knife stereotactic radiosurgery

Abstract

This work illustrates a procedure to assess the overall accuracy associated with Gamma Knife treatment planning using plugging. The main role of source plugging or blocking is to create dose falloff in the junction between a target and a critical structure. We report the use of MAGAT gel dosimeter for verification of an experimental treatment plan based on plugging. The polymer gel contained in a head‐sized glass container simulated all major aspects of the treatment process of Gamma Knife radiosurgery. The 3D dose distribution recorded in the gel dosimeter was read using a 1.5T MRI scanner. Scanning protocol was: CPMG pulse sequence with 8 equidistant echoes, TR=7 s, echo step=14 ms, pixel size=0.5 mm x 0.5 mm, and slice thickness of 2 mm. Using a calibration relationship between absorbed dose and spin‐spin relaxation rate (R2), we converted R2 images to dose images. Volumetric dose comparison between treatment planning system (TPS) and gel measurement was accomplished using an in‐house MATLAB‐based program. The isodose overlay of the measured and computed dose distribution on axial planes was in close agreement. Gamma index analysis of 3D data showed more than 94% voxel pass rate for different tolerance criteria of 3%/2 mm, 3%/1 mm and 2%/2 mm. Film dosimetry with GAFCHROMIC EBT 2 film was also performed to compare the results with the calculated TPS dose. Gamma index analysis of film measurement for the same tolerance criteria used for gel measurement evaluation showed more than 95% voxel pass rate. Verification of gamma plan calculated dose on account of shield is not part of acceptance testing of Leksell Gamma Knife (LGK). Through this study we accomplished a volumetric comparison of dose distributions measured with a polymer gel dosimeter and Leksell GammaPlan (LGP) calculations for plans using plugging. We propose gel dosimeter as a quality assurance (QA) tool for verification of plug‐based planning.PACS number: 87.53.Ly, 87.55.‐x, 87.56.N‐

Verification of Gamma Knife extend system based fractionated treatment planning using EBT2 film

“…Figure 9 represents the differential dose area histogram (DDAH). 5,6,13 A reasonable agreement was achieved between calculated and measured dose in the sagittal plane as shown in Fig. 9(a).…”

“…11 A Graphical User Interface designed inhouse with MATLAB was used for this comparative study. 6,13,14 The program was used to plot isodose overlay, gamma index analysis and dose volume histograms for comparison study. The extracted TPS dose was a calculation grid with 31 3 points with grid size 1 mm.…”

Indigenously developed multipurpose acrylic head phantom for verification of IMRT using film and gel dosimetry

“…Through this work we have developed tools which were already tested for 3D measurements to perform measurements and analyses in a radiation oncology clinic using normoxic gels. ( 12 , 13 , 14 ) We have used the same tools with minor modifications for verification of IMRT plan.…”

Radiation Dosimetry by Use of Radiosensitive Hydrogels and Polymers: Mechanisms, State-of-the-Art and Perspective from 3D to 4D

“…As most polymer gel dosimeters are used with larger doses than those provided in a single fraction, many studies have focused on stereotactic radiosurgery where larger doses are delivered [ 73 , 83 , 234 , 284 , 285 , 286 , 287 , 288 , 289 , 290 , 291 , 292 , 293 , 294 , 295 ]. In most of the studies, the emphasis of the treatment validation experiment is on the spatial accuracy rather than on the absolute dose delivery.…”