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 Epidermal Growth Factor Receptor Mutation on Intracranial Progression-Free Survival of Non-Small Cell Lung Cancer Patients with Brain Metastasis Underwent Gamma Knife Radiosurgery

Background@#The aim of this study was to survey prognostic factors, particularly those focusing on epidermal growth factor receptor (EGFR) mutations, of patients with non-small cell lung cancer (NSCLC) after Gamma Knife Radiosurgery (GKRS) for metastatic brain tumors. @*Methods@#We retrospectively reviewed the medical records of 98 patients with NSCLC who underwent GKRS for brain metastases from August 2010 to July 2017. The primary endpoint was progression-free survival (PFS) of the intracranial disease. We analyzed variables such as age, sex, Karnofsky Performance Status, recursive partitioning analysis (RPA) class, smoking status, primary cancer pathology, EGFR mutations, and time to brain metastases as prognostic factors. @*Results@#The median overall survival (OS) of the patients was 16 months [95% confidence interval (CI), 13-21 months]. Median systemic PFS and intracranial PFS were 9 months (95% CI, 8-11 months) and 11 months (95% CI, 7-14 months), respectively. Kaplan-Meier survival analysis revealed that the patients with EGFR mutations had longer intracranial PFS than those without EGFR mutation (median intracranial PFS: 19 vs. 10 months with p=0.01) while they had no benefits in OS and systemic PFS. Furthermore, the patients harboring adenocarcinoma had longer OS ( p<0.01) and intracranial PFS ( p<0.01) and the patients with lower RPA class had longer OS ( p=0.02) and intracranial PFS ( p=0.03). @*Conclusion@#EGFR mutations, primary cancer pathology, and RPA class may be proposed as prognostic factors for intracranial PFS in NSCLC patients after GKRS for brain metastasis in this study.

Reliability of Stereotactic Coordinates of 1.5-Tesla and 3-Tesla MRI in Radiosurgery and Functional Neurosurgery

OBJECTIVE: The aims of this study are to identify interpersonal differences in defining coordinates and to figure out the degree of distortion of the MRI and compare the accuracy between CT, 1.5-tesla (T) and 3.0T MRI. METHODS: We compared coordinates in the CT images defined by 2 neurosurgeons. We also calculated the errors of 1.5T MRI and those of 3.0T. We compared the errors of the 1.5T with those of the 3.0T. In addition, we compared the errors in each sequence and in each axis. RESULTS: The mean difference in the CT images between the two neurosurgeons was 0.48+/-0.22 mm. The mean errors of the 1.5T were 1.55+/-0.48 mm (T1), 0.75+/-0.38 (T2), and 1.07+/-0.57 (FLAIR) and those of the 3.0T were 2.35+/-0.53 (T1), 2.18+/-0.76 (T2), and 2.16+/-0.77 (FLAIR). The smallest mean errors out of all the axes were in the x axis : 0.28-0.34 (1.5T) and 0.31-0.52 (3.0T). The smallest errors out of all the MRI sequences were in the T2 : 0.29-0.58 (1.5T) and 0.31-1.85 (3.0T). CONCLUSION: There was no interpersonal difference in running the Gamma Plan(R) to define coordinates. The errors of the 3.0T were greater than those of the 1.5T, and these errors were not of an acceptable level. The x coordinate error was the smallest and the z coordinate error was the greatest regardless of the MRI sequence. The T2 sequence was the most accurate sequence.