Validation of Gamma Knife Perfexion Dose Profile Distribution by a Modified Variable Ellipsoid Modeling Technique

Objective@#: High precision and accuracy are expected in gamma knife radiosurgery treatment. Because of the requirement of clinically applying complex radiation and dose gradients together with a rapid radiation decline, a dedicated quality assurance program is required to maintain the radiation dosimetry and geometric accuracy and to reduce all associated risk factors. This study investigates the validity of Leksell Gamma plan (LGP)10.1.1 system of 5th generation Gamma Knife Perfexion as modified variable ellipsoid modeling technique (VEMT) method. @*Methods@#: To verify LGP10.1.1 system, we compare the treatment plan program system of the Gamma Knife Perfexion, that is, the LGP, with the calculated value of the proposed modified VEMT program. To verify a modified VEMT method, we compare the distributions of the dose of Gamma Knife Perfexion measured by Gafchromic EBT3 and EBT-XD films. For verification, the center of an 80 mm radius solid water phantom is placed in the center of all sectors positioned at 16 mm, 4 mm and 8 mm; that is, the dose distribution is similar to the method used in the x, y, and z directions by the VEMT. The dose distribution in the axial direction is compared and analyzed based on Full-Width-of-Half-Maximum (FWHM) evaluation. @*Results@#: The dose profile distribution was evaluated by FWHM, and it showed an average difference of 0.104 mm for the LGP value and 0.130 mm for the EBT-XD film. @*Conclusion@#: The modified VEMT yielded consistent results in the two processes. The use of the modified VEMT as a verification tool can enable the system to stably test and operate the Gamma Knife Perfexion treatment planning system.

The Effect of Pain Reduction during Headframe Fixation for Stereotactic Radiosurgery by the Preceded Local Anesthesia under the Needle Cap Guidance

BACKGROUND: Gamma knife radiosurgery (GKRS) has become a major alternative in the neurosurgical field. However, many patients complained of considerable discomfort during the fixation of rigid headframe. This study investigated whether our modified procedure could reduce fixation-related pain. METHODS: Sixty-six patients who underwent GKRS were enrolled in this study. Thirty-one patients (Group A) underwent the conventional subcutaneous infiltration technique, and 35 patients (Group B) did the modified procedure. In group A, the headframe was held in position by an assistant, and local anesthetics were injected subcutaneously using a 23-gauge spinal needle at pinning sites. Subsequently, pins were applied according to measurements based on spinal needle depth. In group B, with the frame held in position by an assistant, pin sites were marked with a surgical pen under the guidance of needle cap placed on the pin holes. The head frame was then removed, and local anesthetics were injected subcutaneously and periosteally at each marked pin site using a 26-gauge needle. The headframe was then repositioned 5 minutes after local infiltration, and pins were applied according to measurements based on spinal needle depth. To evaluate pain severity during procedures, visual analogue scale (VAS) scores were recorded during local infiltration and frame placement with pins. The pain scores of the two groups were analyzed statistically. RESULTS: Group B had a significantly lower VAS score during frame placement than group A (7.26 vs. 3.61; p<0.001), and mean VAS score at local infiltration was also significantly lower in group B (4.74 vs. 3.74; p=0.008). CONCLUSION: Patients in group B experienced significantly less pain than those in group A during pin placement. Pre-fixation time advanced local anesthesia might reduce pain during stereotactic procedures, and the use of a 26-gauge needle appeared in less pain during local infiltration.

Gamma Knife Radiosurgery in Recurrent Trigeminal Neuralgia after Other Procedures / 고신대학교의과대학학술지

OBJECTIVES: Trigeminal neuralgia (TN) is undurable paroxysmal pain in the distribution of the fifth cranial nerve. Invasive treatment modalities for TN include microvascular decompression (MVD) and percutaneous procedures, such as, radiofrequency rhizotomy (RFR). Gamma Knife radiosurgery (GKRS) is a considerable option for patients with pain recurrence after an initial procedure. This study was undertaken to analyze the effects of gamma knife radiosurgery in recurrent TN after other procedures. METHODS: Eleven recurrent TN patients after other procedures underwent GKRS in our hospital from September 2004 to August 2016. Seven patients had previously undergone MVD alone, two underwent MVD with partial sensory rhizotomy (PSR), and two underwent RFR. Mean patient age was 60.5 years. We retrospectively analyzed patient's characteristics, clinical results, sites, and divisions of pain. Outcomes were evaluated using the Visual Analog Scales (VAS) score. RESULTS: Right sides were more prevalent than left sides (7:4). The most common distribution of pain was V1 + V2 division (n = 5) following V2 + V3 (n = 3), V2 (n = 2), and V1 + V2 + V3 (n = 1) division. Median GKRS dose was 80 Gy and the mean interval between the prior treatment and GKRS was 74.45 months. The final outcomes of subsequent GKRS were satisfactory in most cases, and at 12 months postoperatively ten patients (90.0%) had a VAS score of ≤ 3. CONCLUSIONS: In this study, the clinical result of GKRS was satisfactory. Invasive procedures, such as, MVD, RFR are initially effective in TN patients, but GKRS provides a safe and satisfactory treatment modality for those who recurred after prior invasive treatments.

Clinical Application of Gamma Knife Dose Verification Method in Multiple Brain Tumors : Modified Variable Ellipsoid Modeling Technique

OBJECTIVE: The Leksell Gamma Knife(R) (LGK) is based on a single-fraction high dose treatment strategy. Therefore, independent verification of the Leksell GammaPlan(R) (LGP) is important for ensuring patient safety and minimizing the risk of treatment errors. Although several verification techniques have been previously developed and reported, no method has ever been tested statistically on multiple LGK target treatments. The purpose of this study was to perform and to evaluate the accuracy of a verification method (modified variable ellipsoid modeling technique, MVEMT) for multiple target treatments. METHODS: A total of 500 locations in 10 consecutive patients with multiple brain tumor targets were included in this study. We compared the data from an LGP planning system and MVEMT in terms of dose at random points, maximal dose points, and target volumes. All data was analyzed by t-test and the Bland-Altman plot, which are statistical methods used to compare two different measurement techniques. RESULTS: No statistical difference in dose at the 500 random points was observed between LGP and MVEMT. Differences in maximal dose ranged from -2.4% to 6.1%. An average distance of 1.6 mm between the maximal dose points was observed when comparing the two methods. CONCLUSION: Statistical analyses demonstrated that MVEMT was in excellent agreement with LGP when planning for radiosurgery involving multiple target treatments. MVEMT is a useful, independent tool for planning multiple target treatment that provides statistically identical data to that produced by LGP. Findings from the present study indicate that MVEMT can be used as a reference dose verification system for multiple tumors.

The Variable Ellipsoid Modeling Technique as a Verification Method for the Treatment Planning System of Gamma Knife Radiosurgery

OBJECTIVE: The secondary verification of Leksell Gamma Knife treatment planning system (LGP) (which is the primary verification system) is extremely important in order to minimize the risk of treatment errors. Although prior methods have been developed to verify maximum dose and treatment time, none have studied maximum dose coordinates and treatment volume. METHODS: We simulated the skull shape as an ellipsoid with its center at the junction between the mammillary bodies and the brain stem. The radiation depths of the beamlets emitted from 201 collimators were calculated based on the relationship between this ellipsoid and a single beamlet expressed as a straight line. A computer program was coded to execute the algorithm. A database system was adopted to log the doses for 31x31x31 or 29,791 matrix points allowing for future queries to be made of the matrix of interest. RESULTS: When we compared the parameters in seven patients, all parameters showed good correlation. The number of matrix points with a dose higher than 30% of the maximal dose was within +/- 2% of LGP. The 50% dose volume, which is generally the target volume, differs maximally by 4.2%. The difference of the maximal dose ranges from 0.7% to 7%. CONCLUSION: Based on the results, the variable ellipsoid modeling technique or variable ellipsoid modeling technique (VEMT) can be a useful and independent tool to verify the important parameters of LGP and make up for LGP.