Investigation of optimal planning strategy in gamma knife perfexion for vestibular schwannoma tumor using hybrid plan technique.

Purpose.Stereotactic radiosurgery (SRS) for vestibular schwannoma (VS) is clinically challenging because of surrounding critical structures. We generated and compared the forward plan (FP), inverse plan (IP), and hybrid plan (HP) for the optimal planning strategy in Gamma Knife stereotactic radiosurgery (GKSRS) for vestibular schwannoma tumors (VS).Methods and materials. In this study, 51 planning scenarios of 17 patients with VS were planned for GKSRS using FP, IP, and HP in Leksell Gamma plan (LGP10.1) using the TMR10 algorithm. The planning images were obtained using the following MRI (GE, USA) scan parameters: T1W images-MPRAGE sequence, FOV-256 mm × 256 mm, matrix size-512 mm × 512 mm, and the slice thickness 1 mm. The total dose was prescribed12Gy and normalized at 50% isodose level.Results and discussion. The plan parameters were compared dosimetrically by maintaining FP as a base plan. The statistical analysis, including one-factor, repeated measures ANOVA and Bonferroni correction tests, were performed. The p-value for planning parameters such as brainstem dose, beam ON time, and gradient index significantly favored HP.Conclusion. Overall results show that HP is an efficient method for GKSRS of VS The p-value was less than 0.001 and statistically significant for various plan indices.

A practical strategy for incorporating the convolution algorithm in Leksell GammaPlan for routine treatment planning†.

Purpose: This study aims to establish criteria for convolution dose calculations and an efficient procedure to include the heterogeneity effects in GammaKnife radiosurgery (GKRS) treatment plans. Methods and materials: We analyzed 114 GKRS cases of various disease types, tumor locations, sizes, the number of fractions, and prescription doses. There was a total of 205 tumors. CT scans were performed in addition to routine MRI scans for all treatments. All treatment plans were created using the TMR10 algorithm (TMR10). We repeated the dose calculations for this study with the convolution algorithm (Conv). We calculated the ratios between Conv and TMR10 of the treatment volume (TxtVol), the volume covered by half of the prescription dose (TxtVol2), the minimum, maximum, and mean doses in the tumor (minDose, maxDose, and meanDose), and the volume of tumor covered by the prescription isodose (covVol). We then categorized those quantities for locations of tumors represented by the shortest distance of the skull surface from the tumor center (distC) and the tumor edge (distE). [Table: see text]. Results: All six ratios increased with increasing distC and distE. For example, the median minDose ratio increased from 0.885 to 0.933 as distE increased. There was a statistically significant difference in the minDose ratio between tumors of distE < 2 cm and distE ≥ 2 cm. On the other hand, the median maxDose ratio was about 0.933 [0.928-0.939], being almost independent of distE. This suggested a 6.1% overestimation of the delivered dose with TMR10. Conclusion: The heterogeneity effects must be considered for the volume dose calculations by applying the convolution algorithm when the distance of the skull surface from the closest point of the tumor is less than 2 cm to achieve less than 3% accuracy.

Evaluation of two calibration methods for MRI-based polymer gel dosimetry.

Polymer gel dosimetry (PGD) can provide three-dimensional (3D) dose data for evaluation of the dose calculation algorithms used by treatment planning systems (TPS). Although the PGD technique, particularly with MRI, is now ready for clinical applications, an accurate calibration method is vital for treatment validation in 3D. This study evaluated the single-phantom electron beam (SPE) method that used the depth-dose data of a 9 MeV electron beam. This technique was compared with the multi-vial x-ray (MVX) method that used nine small vials irradiated with various doses. We tested two regression equations, i.e., third-order polynomial and tangent functions, and two dose-normalization methods, i.e., one-point and two-point methods. These methods were evaluated using a dose distribution generated by a 3 cm × 3 cm open arc beam. We used MAGAT polymer gel manufactured in-house. We found that the SPE method required a smaller dose scaling for the dose comparison. The tangent function showed better data fitting than the polynomial function with smaller uncertainty of the estimated coefficients. We did not observe a distinct advantage of the SPE method over the MVX method for the 3D dose comparison with the test case. From this study, we infer that the SPE method with the tangent function as the regression equation and one-point dose normalization is a good calibration option for the MRI-based polymer gel dosimetry.

Diacetylene-Based Colorimetric Radiation Sensors for the Detection and Measurement of γ Radiation during Blood Irradiation.

Blood and its cellular components are irradiated by ionizing radiation before transfusion to prevent the proliferation of viable T lymphocytes which cause transfusion associated-graft versus host disease. The immunodeficient patients undergoing chemotherapy for various malignancies are at risk of this disease. The international guidelines for blood transfusion recommend a minimum radiation exposure of 25 Gray (Gy) to the midplane of the blood bag, while a minimum dose of 15 Gy and a maximum dose of 50 Gy should be given to each portion of the blood bag. Therefore, precise dosimetry of the blood irradiator is essential to ensure the adequate irradiation of the blood components. The paper presents the fabrication of diacetylene-based colorimetric film dosimeters for the verification of irradiated doses. The diacetylene analogues are synthesized by tailoring them with different amide-based headgroups followed by their coating to develop colorimetric film dosimeters. Among all the synthesized diacetylene analogues, aminofluorene-substituted diacetylene exhibits the most significant color transition from white to blue color at a minimum γ radiation dose of 5 Gy. The quantitative study of color change is performed by the digitization of the scanned images of film dosimeters. The digital image processing of the developed film dosimeters facilitates rapid dose measurement which enables their facile implementation and promising application in routine blood irradiator dosimetry.

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

PURPOSE: This paper presents EBT2 film verification of fractionated treatment planning with the Gamma Knife (GK) extend system, a relocatable frame system for multiple-fraction or serial multiple-session radiosurgery. METHODS: A human head shaped phantom simulated the verification process for fractionated Gamma Knife treatment. Phantom preparation for Extend Frame based treatment planning involved creating a dental impression, fitting the phantom to the frame system, and acquiring a stereotactic computed tomography (CT) scan. A CT scan (Siemens, Emotion 6) of the phantom was obtained with following parameters: Tube voltage--110 kV, tube current--280 mA, pixel size--0.5 × 0.5 and 1 mm slice thickness. A treatment plan with two 8 mm collimator shots and three sectors blocking in each shot was made. Dose prescription of 4 Gy at 100% was delivered for the first fraction out of the two fractions planned. Gafchromic EBT2 film (ISP Wayne, NJ) was used as 2D verification dosimeter in this process. Films were cut and placed inside the film insert of the phantom for treatment dose delivery. Meanwhile a set of films from the same batch were exposed from 0 to 12 Gy doses for calibration purposes. An EPSON (Expression 10000 XL) scanner was used for scanning the exposed films in transparency mode. Scanned films were analyzed with inhouse written MATLAB codes. RESULTS: Gamma index analysis of film measurement in comparison with TPS calculated dose resulted in high pass rates >90% for tolerance criteria of 1%∕1 mm. The isodose overlay and linear dose profiles of film measured and computed dose distribution on sagittal and coronal plane were in close agreement. CONCLUSIONS: Through this study, the authors propose treatment verification QA method for Extend frame based fractionated Gamma Knife radiosurgery using EBT2 film.

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

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 = 0.5mm × 0.5mm, 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.