PDF(Pubmed)
Abstract：
OBJECTIVE: To characterize detector array spacing and gamma index for quality assurance (QA) of stereotactic radiosurgery (SRS) deliveries. Use the Nyquist theorem to determine the required detector spacing in SRS fields, and find optimal gamma indices to detect MLC errors using the SRS MapCHECK, ArcCHECK, and a portal imaging device (EPID).
METHODS: The required detector spacing was determined via Fourier analysis of small radiation fields and profiles of typical SRS treatment plans. The clinical impact of MLC errors of 0.5, 1, and 2 mm was evaluated. Global gamma (low-dose threshold 10%) was evaluated for the three detector systems using various combinations of the distance to agreement and the dose difference.
RESULTS: While MLC errors only slightly affected mean dose to PTV and a 2 mm thick surrounding structure (PTV_2 mm), significant PTV underdose incurred with increase in maximum dose to PTV_2 mm. Gamma indices with highest sensitivity to the introduced errors at 95% tolerance level for plans on target volumes of 3.2 cm3 (plan 3 cc) and 35.02 cm3 (plan 35 cc) were 2%/1 mm for the SRS MapCHECK and 2%/3 mm for the ArcCHECK, with 3%/1 mm (plan 3cc) and 2%/1 mm (plan 35cc) for the EPID. Drops in passing rates for a 2 mm MLC error were (46.2%, 41.6%) for the SRS MapCHECK and (12.2%, 4.2%) for the ArcCHECK for plan 3cc and plan 35cc, respectively. For Portal Dose, values were 4.5% (plan 3cc) and 7% (plan 35cc). The Nyquist frequency of two SRS dose distributions lie between 0.26 and 0.1 mm-1 , corresponding to detector spacings of 1.9 and 5 mm. Evaluation of SRS MapCHECK data with doubled detector density indicates that increased detector density may reduce the system\'s sensitivity to errors, necessitating a tighter gamma index.
CONCLUSIONS: The present results give insight on the performance of detector arrays and gamma indices for the investigated detectors during SRS QA.
METHODS: The required detector spacing was determined via Fourier analysis of small radiation fields and profiles of typical SRS treatment plans. The clinical impact of MLC errors of 0.5, 1, and 2 mm was evaluated. Global gamma (low-dose threshold 10%) was evaluated for the three detector systems using various combinations of the distance to agreement and the dose difference.
RESULTS: While MLC errors only slightly affected mean dose to PTV and a 2 mm thick surrounding structure (PTV_2 mm), significant PTV underdose incurred with increase in maximum dose to PTV_2 mm. Gamma indices with highest sensitivity to the introduced errors at 95% tolerance level for plans on target volumes of 3.2 cm3 (plan 3 cc) and 35.02 cm3 (plan 35 cc) were 2%/1 mm for the SRS MapCHECK and 2%/3 mm for the ArcCHECK, with 3%/1 mm (plan 3cc) and 2%/1 mm (plan 35cc) for the EPID. Drops in passing rates for a 2 mm MLC error were (46.2%, 41.6%) for the SRS MapCHECK and (12.2%, 4.2%) for the ArcCHECK for plan 3cc and plan 35cc, respectively. For Portal Dose, values were 4.5% (plan 3cc) and 7% (plan 35cc). The Nyquist frequency of two SRS dose distributions lie between 0.26 and 0.1 mm-1 , corresponding to detector spacings of 1.9 and 5 mm. Evaluation of SRS MapCHECK data with doubled detector density indicates that increased detector density may reduce the system\'s sensitivity to errors, necessitating a tighter gamma index.
CONCLUSIONS: The present results give insight on the performance of detector arrays and gamma indices for the investigated detectors during SRS QA.
摘要：
目的：表征探测器阵列间距和伽玛指数，以保证立体定向放射外科（SRS）分娩的质量保证（QA）。使用奈奎斯特定理确定SRS字段中所需的检测器间距，并使用SRSMapCHECK找到最佳的伽马指数来检测MLC错误，ArcCHECK,和射野成像装置(EPID)。
方法：通过对典型SRS治疗计划的小辐射场和轮廓的傅立叶分析来确定所需的检测器间距。评估了0.5、1和2mm的MLC误差的临床影响。使用协议距离和剂量差的各种组合评估了三个检测器系统的全局伽马（低剂量阈值10％）。
结果：虽然MLC错误仅对PTV和2毫米厚的周围结构（PTV_2毫米）的平均剂量产生轻微影响，随着最大剂量增加到PTV_2mm，出现显著的PTV剂量不足。对于目标体积为3.2cm3（计划3cc）和35.02cm3（计划35cc）的计划，在95％的容差水平下，对引入的误差具有最高敏感性的Gamma指数对于SRSMapCHECK为2％/1mm，对于ArcCHECK为2％/3mm。EPID为3%/1毫米(计划3cc)和2%/1毫米(计划35cc)。2mmMLC误差的合格率下降为(46.2%，41.6％）对于SRSMapCHECK和（12.2％，4.2%)用于计划3cc和计划35cc的ArcCHECK，分别。对于门户剂量，值分别为4.5%(计划3cc)和7%(计划35cc)。两个SRS剂量分布的奈奎斯特频率介于0.26和0.1mm-1之间，对应于1.9和5毫米的探测器间距。对探测器密度加倍的SRSMapCHECK数据的评估表明，增加的探测器密度可能会降低系统对错误的敏感性，需要更严格的伽马指数。
结论：目前的结果提供了有关SRSQA期间所研究探测器的探测器阵列性能和伽马指数的见解。
方法：通过对典型SRS治疗计划的小辐射场和轮廓的傅立叶分析来确定所需的检测器间距。评估了0.5、1和2mm的MLC误差的临床影响。使用协议距离和剂量差的各种组合评估了三个检测器系统的全局伽马（低剂量阈值10％）。
结果：虽然MLC错误仅对PTV和2毫米厚的周围结构（PTV_2毫米）的平均剂量产生轻微影响，随着最大剂量增加到PTV_2mm，出现显著的PTV剂量不足。对于目标体积为3.2cm3（计划3cc）和35.02cm3（计划35cc）的计划，在95％的容差水平下，对引入的误差具有最高敏感性的Gamma指数对于SRSMapCHECK为2％/1mm，对于ArcCHECK为2％/3mm。EPID为3%/1毫米(计划3cc)和2%/1毫米(计划35cc)。2mmMLC误差的合格率下降为(46.2%，41.6％）对于SRSMapCHECK和（12.2％，4.2%)用于计划3cc和计划35cc的ArcCHECK，分别。对于门户剂量，值分别为4.5%(计划3cc)和7%(计划35cc)。两个SRS剂量分布的奈奎斯特频率介于0.26和0.1mm-1之间，对应于1.9和5毫米的探测器间距。对探测器密度加倍的SRSMapCHECK数据的评估表明，增加的探测器密度可能会降低系统对错误的敏感性，需要更严格的伽马指数。
结论：目前的结果提供了有关SRSQA期间所研究探测器的探测器阵列性能和伽马指数的见解。
