The Alignment Evaluation for Patient Positioning System(PPS) of Gamma Knife PerfexionTM

The purpose of this study is to assess the mechanical stability and alignment of the patient positioning system (PPS) of Leksell Gamma Knife Perfexion(LGK PFX). The alignment of the PPS of the LGK PFX was evaluated through measurements of the deviation of the coincidence of the Radiological Focus Point(RFP) and the PPS Calibration Center Point(CCP) applying different weights on the couch(0, 50, 60, 70, 80, and 90 kg). In measurements, a service diode test tool with three diode detectors being used biannually at the time of the routine preventive maintenance was used. The test conducted with varying weights on the PPS using the service diode test tool measured the radial deviations for all three collimators 4, 8, and 16 mm and also for three different positions of the PPS. In order to evaluate the alignment of the PPS, the radial deviations of the correspondence of the radiation focus and the LGK calibration center point of multiple beams were averaged using the calibrated service diode test tool at three university hospitals in Busan and Gyeongnam. Looking at the center diode for all collimators 4, 8, and 16 mm without weight on the PPS, and examining the short and long diodes for the 4 mm collimator, the means of the validation difference, i.e., the radial deviation for the setting of 4, 8, and 16 mm collimators for the center diode were respectively measured to 0.058 ± 0.023, 0.079 ± 0.023, and 0.097 ± 0.049 mm, and when the 4 mm collimator was applied to the center diode, the short diode, and the long diode, the average of the radial deviation was respectively 0.058 ± 0.023, 0.078 ± 0.01 and 0.070 ± 0.023 mm. The average of the radial deviations when irradiating 8 and 16 mm collimators on short and long diodes without weight are measured to 0.07 ± 0.003(8 mm sd), 0.153 ± 0.002 mm(16 mm sd) and 0.031 ± 0.014(8 mm ld), 0.175 ± 0.01 mm(16 mm ld) respectively. When various weights of 50 to 90 kg are placed on the PPS, the average of radial deviation when irradiated to the center diode for 4, 8, and 16 mm is 0.061 ± 0.041 to 0.075 ± 0.015, 0.023 ± 0.004 to 0.034 ± 0.003, and 0.158 ± 0.08 to 0.17 ± 0.043 mm, respectively. In addition, in the same situation, when the short diode for 4, 8, and 16 mm was irradiated, the averages of radial deviations were 0.063 ± 0.024 to 0.07 ± 0.017, 0.037 ± 0.006 to 0.059 ± 0.001, and 0.154 ± 0.03 to 0.165 ± 0.07 mm, respectively. In addition, when irradiated on long diode for 4, 8, and 16 mm, the averages of radial deviations were measured to be 0.102 ± 0.029 to 0.124 ± 0.036, 0.035 ± 0.004 to 0.054 ± 0.02, and 0.183 ± 0.092 to 0.202 ± 0.012 mm, respectively. It was confirmed that all the verification results performed were in accordance with the manufacturer's allowable deviation criteria. It was found that weight dependence was negligible as a result of measuring the alignment according to various weights placed on the PPS that mimics the actual treatment environment. In particular, no further adjustment or recalibration of the PPS was required during the verification. It has been confirmed that the verification test of the PPS according to various weights is suitable for normal Quality Assurance of LGK PFX.

감마나이프 퍼펙션의 자동환자이송장치에 대한 정렬됨 평가

본 연구는 렉셀 감마나이프 퍼펙션 모델에서 다양한 무게를 가진 자동환자이송장치의 안정성 즉 정렬됨 평가를 위함이다. 퍼펙션 자동환자이송장치의 정렬됨을 평가하기 위해서 부산, 경남 소재 3개 대학병원에서 교정된 서비스 다이오드 테스트 도구를 사용하여 다중 빔의 방사선 초점과 감마나이프 교정 중심점의 일치성에 대한 방사상 편차 △r을 측정하여 평균하였다. 자동환자이송장치 상에 무게 없이 모든 콜리메이터 4, 8, 16 mm에 대한 중심 다이오드에 조사와 4 mm 콜리메이터에 대한 짧은 다이오드와 긴 다이오드에 조사한 경우를 살펴보면 중심 다이오드에 4, 8, 16 mm 콜리메이터 각각 조사 시 검증 차이 즉 방사상 편차의 평균은 각각 0.058 ± 0.023, 0.079 ± 0.023, 0.097 ± 0.049 mm로 나타났고, 중심 다이오드, 짧은 다이오드와 긴 다이오드에 4 mm 콜리메이터 조사 시 방사상 편차의 평균은 각각 0.058 ± 0.023, 0.078 ± 0.01, 0.070 ± 0.023 mm로 나타났다. 무게 없이 짧은 다이오드와 긴 다이오드에 8, 16 mm 조사 시 방사상 편차의 평균은 각각 0.07 ± 0.003(8 mm sd), 0.153 ± 0.002 mm(16 mm sd)와 0.031 ± 0.014(8 mm ld), 0.175 ± 0.01 mm(16 mm ld)로 측정되었다. 다양한 무게 50 ~ 90 kg을 자동환자이송장치에 올린 경우 4, 8, 16 mm에 대한 중심 다이오드에 조사 시 방사상 편차의 평균은 각각 0.061±0.041 ~ 0.075±0.015, 0.023±0.004 ~ 0.034±0.003, 0.158±0.08 ~ 0.17±0.043 mm를 나타냈다. 또한 동일한 상황에서 4, 8, 16 mm에 대한 짧은 다이오드에 조사 시 방사상 편차의 평균은 각각 0.063±0.024 ~ 0.07±0.017, 0.037±0.006 ~ 0.059±0.001, 0.154±0.03 ~ 0.165±0.07 mm로 나타났다. 그리고 4, 8, 16 mm에 대한 긴 다이오드에 조사 시 방사상 편차의 평균이 각각 0.102±0.029 ~ 0.124±0.036, 0.035±0.004 ~ 0.054±0.02, 0.183±0.092 ~ 0.202±0.012 mm로 측정되었다. 수행된 모든 검증 결과는 제조사의 허용 편차 기준에 적합함을 확인할 수 있었다. 실제 치료 환경을 흉내 낸 자동환자이송장치에 올린 다양한 무게에 따른 정렬됨의 측정 결과 무게 의존성은 무시할 수 있음을 알 수 있었다. 저자들은 다양한 무게에 따른 자동환자이송장치의 검증 테스트가 렉셀 감마나이프 퍼펙션의 통상적인 정도관리를 위하여 적합한 것으로 확인하였다.