The Outcome of Gamma Knife Radiosurgery for Facial Pain Varies by Pre-treatment Burchiel Classification Pain Type: Results From 256 Gamma Knife Radiosurgery Procedures for Facial Pain
Thomas L. EllisChristopher J. BalamuckiA.F. deGuzmanJames LovatoEdward G. ShawStephen B. TatterK. EkstrandJ. Daniel BourlandCharles L. BranchMichael T. MunleyT.W. HuangVolker W. Stieber
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Purpose: To assess the impacts that multileaf collimator (MLC) leaf width has on the dose conformity and normal brain tissue doses of single and multiple isocenter stereotactic IMRT (SRT) plans for multiple intracranial tumors. Methods: Fourteen patients with 2–3 targets were studied retrospectively. Patients treated with multiple isocenter treatment plans using 9 to 12 non‐coplanar beams per lesion underwent repeat planning using single isocenter and 10 to 12 non‐coplanar beams with 2.5mm, 3mm and 5mm MLC leaf widths. Brainlab iPlan treatment planning system for delivery with the 2.5mm MLC served as reference. Identical contour sets and dose‐volume constraints were applied. The prescribed dose to each target was 25 Gy to be delivered over 5 fractions with a minimum of 99% dose to cover ≥ 95% of the target volume. Results: The lesions and normal brains ranged in size from 0.11 to 51.67cc (median, 2.75cc) and 1090 to 1641cc (median, 1401cc), respectively. The Paddick conformity index for single and multiple isocenter (2.5mm vs. 3mm and 5mm MLCs) was (0.79±0.08 vs. 0.79±0.07 and 0.77±0.08) and (0.79±0.09 vs. 0.77±0.09 and 0.76±0.08), respectively. The average normal brain volumes receiving 15 Gy for single and multiple isocenter (2.5mm vs. 3mm and 5mm MLCs) were (3.65% vs. 3.95% and 4.09%) and (2.89% vs. 2.91% and 2.92%), respectively. Conclusion: The average dose conformity observed for the different leaf width for single and multiple isocenter plans were similar, throughout. However, the average normal brain volumes receiving 2.5 to 15 Gy were consistently lower for the 2.5mm MLC leaf width, especially for single isocenter plans. The clinical consequences of these integral normal brain tissue doses are still unknown, but employing the use of the 2.5mm MLC option is desirable at sparing normal brain tissue for both single and multiple isocenter cases.
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The purpose of this study was to determine with phantom and patient imaging the effect of an automatic patient-centering technique on the radiation dose associated with MDCT.A 32-cm CT dose index (CTDI) phantom was scanned with 64-MDCT in three positions: gantry isocenter and 30 and 60 mm below the isocenter of the scanner gantry. In each position, surface, peripheral, and volume CTDIs were estimated with a standard 10-cm pencil ionization chamber. The institutional review board approved the study with 63 patients (36 men, 27 women; mean age, 51 years; age range, 22-83 years) undergoing chest (n = 18) or abdominal (n = 45) CT using the z-axis automatic exposure control technique. Each patient was positioned according to the region being scanned and then was centered in the gantry. Before scanning of a patient, automatic centering software was used to estimate patient off-centering and percentage of dose reduction with optimum recentering. Data were analyzed with linear correlation and the Student's t test.Peripheral and surface CTDIs increased approximately 12-18% with 30-mm off-center distance and 41-49% with 60-mm off-center distance. Approximately 95% (60/63) of patients were not positioned accurately in the gantry isocenter. The mean radiation dose saving with automatic centering of all patients was 13.0% +/- 0.9% (range, 2.6-29.9%). There was strong correlation between off-center distance and percentage of surface CTDI reduction with recentering of patients in the gantry isocenter (r2 = 0.85, p < 0.0001).Surfaces doses can be reduced if radiologic technologists can better center patients within the CT gantry. Automatic centering technique can help in optimum patient centering and result in as much as 30% reduction in surface dose.
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Objective: To study the accuracy of SRS200 linac radiosurgery system in our hospital. Methods: The CT localization accuracy of linac radiosurgery system was measured by markers in skull phantom, and the accuracy of isocenter subsystem and common error by film method. Results: The accuracy of CT localization of BRW headring was 0.65 ?mm and maximum error was 1.09?mm. The accuracy of SRS200 isocenter subsystem was 0.19?mm. The common accuracy of linac radiosurgery system was 0.68?mm mathematically and 1.43?mm actually. Conclusion: The accuracy of this linac radiosurgery system has come up to the standard of quality control of stereotactic radiosurgery.
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The goals of stereotactic radiosurgery (SRS) are the ablation of target tissue and sparing of critical normal tissue. We develop tools to aid in the selection of collimation and prescription (Rx) isodose line to optimize the dose gradient for single isocenter intracranial stereotactic radiosurgery (SRS) with GammaKnife 4C utilizing the updated physics data in GammaPlan v10.1.Single isocenter intracranial SRS plans were created to treat the center of a solid water anthropomorphism head phantom for each GammaKnife collimator (4 mm, 8 mm, 14 mm, and 18 mm). The dose gradient, defined as the difference of effective radii of spheres equal to half and full Rx volumes, and Rx treatment volume was analyzed for isodoses from 99% to 20% of Rx.The dosimetric data on Rx volume and dose gradient vs. Rx isodose for each collimator was compiled into an easy to read nomogram as well as plotted graphically. The 4, 8, 14, and 18 mm collimators have the sharpest dose gradient at the 64%, 70%, 76%, and 77% Rx isodose lines, respectively. This corresponds to treating 4.77 mm, 8.86 mm, 14.78 mm, and 18.77 mm diameter targets with dose gradients radii of 1.06 mm, 1.63 mm, 2.54 mm, and 3.17 mm, respectively.We analyzed the dosimetric data for the most recent version of GammaPlan treatment planning software to develop tools that when applied clinically will aid in the selection of a collimator and Rx isodose line for optimal dose gradient and target coverage for single isocenter intracranial SRS with GammaKnife 4C.
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Due to spatial uncertainty, patient setup errors are of major concern for radiosurgery of multiple brain metastases (m-bm) when using single-isocenter/multitarget (SIMT) volumetric modulated arc therapy (VMAT) techniques. However, recent clinical outcome studies show high rates of tumor local control for SIMT-VMAT. In addition to direct cell kill (DCK), another possible explanation includes the effects of indirect cell kill (ICK) via devascularization for a single dose of 15 Gy or more and by inducing a radiation immune intratumor response. This study quantifies the role of indirect cell death in dosimetric errors as a function of spatial patient setup uncertainty for stereotactic treatments of multiple lesions.Nine complex patients with 61 total tumors (2-16 tumors/patient) were planned using SIMT-VMAT with geometry similar to HyperArc with a 10MV-FFF beam (2400 MU/min). Isocenter was placed at the geometric center of all tumors. Average gross tumor volume (GTV) and planning target volume (PTV) were 1.1 cc (0.02-11.5) and 1.9 cc (0.11-18.8) with an average distance to isocenter of 5.4 cm (2.2-8.9). The prescription was 20 Gy to each PTV. Plans were recalculated with induced clinically observable patient setup errors [±2 mm, ±2o ] in all six directions. Boolean structures were generated to calculate the effect of DCK via 20 Gy isodose volume (IDV) and ICK via 15 Gy IDV minus the 20 Gy IDV. Contributions of each IDV to the PTV coverage were analyzed along with normal brain toxicity due to the patient setup uncertainty. Induced uncertainty and minimum dose covering the entire PTV were analyzed to determine the maximum tolerable patient setup errors to utilize the ICK effect for radiosurgery of m-bm via SIMT-VMAT.Patient setup errors of 1.3 mm /1.3° in all six directions must be maintained to achieve PTV coverage of the 15 Gy IDV for ICK. Setup errors of ±2 mm/2° showed clinically unacceptable loss of PTV coverage of 29.4 ± 14.6% even accounting the ICK effect. However, no clinically significant effect on normal brain dosimetry was observed.Radiosurgery of m-bm using SIMT-VMAT treatments have shown positive clinical outcomes even with small residual patient setup errors. These clinical outcomes, while largely due to DCK, may also potentially be due to the ICK. Potential mechanisms, such as devascularization and/or radiation-induced intratumor immune enhancement, should be explored to provide a better understanding of the radiobiological response of stereotactic radiosurgery of m-bm using a SIMT-VMAT plan.
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Purpose:To discuss the clinical applying value of large bore CT simulation in Radiation Oncology.Materials and methods:12 NPC patients and 12 breast cancer patients are simulated by using large bore CT and planed,respectively.The precise verification of isocenter treated:all isocenters treated are secondly scaned with 1.25 cm slice thickness and compared with isocenter planed.The deviations between isocenter treated and isocenter planed in X axis(right left direction),Y axis(superior inferior direction),Z axis(anterior posterior direction)were dx,dy,dz,respectively.Then the distant deviations(Di) between isocenter treated and isocenter planed are calculated.The accuracy verification of isocenter treated:Two orthogonal portal images were taken by EPID,All Portal images were registered automatically into the digitally reconstructed radiography(DRR) Then the deviations between isocenter treated and isocenter planed were calculated in X axis,Y axis,Z axis.Results:12 NPC patients and 12 breast cancer patients are simulated in an optimal treatment position.The precise verification of isocenter treated:the distant deviation(Di)of NPC patients between isocenter treated and isocenter planed is 1.7 mm.the distant deviation(Di)of breast cancer patients between isocenter treated and isocenter planed is 2.7 mm.The accuracy verification of isocenter treated:the deviations of NPC patients between isocenter treated and isocenter planed in X axis,Y axis,Z axis are 0 mm,0.4 mm,-0.4 m,respectively.the deviations of breastcancer patients between isocenter treated and isocenter planed in X axis,Y axis,Z axis are 2.0 mm,2.1 mm,-0.4 mm,respectively.Conclusion:Large bore CT simulation not only can satisfy to scan in an optimal treatment position,but also is accuracy.So it can fully satisfy to develop 3D-CRT and the IMRT radiotherapy.
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For conventional irradiation devices, the radiation isocenter accuracy is determined by star shot measurements on films. In magnetic resonance (MR)-guided radiotherapy devices, the results of this test may be altered by the magnetic field and the need to align the radiation and imaging isocenter may require a modification of measurement procedures. Polymer dosimetry gels (PG) may offer a way to perform both, the radiation and imaging isocenter test, however, first it has to be shown that PG reveal results comparable to the conventionally applied films. Therefore, star shot measurements were performed at a linear accelerator using PG as well as radiochromic films. PG were evaluated using MR imaging and the isocircle radius and the distance between the isocircle center and the room isocenter were determined. Two different types of experiments were performed: i) a standard star-shot isocenter test and (ii) a star shot, where the detectors were placed between the pole shoes of an experimental electro magnet operated either at 0 T or 1 T. For the standard star shot, PG evaluation was independent of the time delay after irradiation (1 h, 24 h, 48 h and 216 h) and the results were comparable to those of film measurements. Within the electro magnet, the isocircle radius increased from 0.39 ± 0.01 mm to 1.37 ± 0.01 mm for the film and from 0.44 ± 0.02 mm to 0.97 ± 0.02 mm for the PG-measurements, respectively. The isocenter distance was essentially dependent on the alignment of the magnet to the isocenter and was between 0.12 ± 0.02 mm and 0.82 ± 0.02 mm. The study demonstrates that evaluation of the PG directly after irradiation is feasible, if only geometrical parameters are of interest. This allows using PG for star shot measurements to evaluate the radiation isocenter accuracy with comparable accuracy as with radiochromic films.
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