Objective:To analyze the dosimetric differences between gamma knife stereotactic body radiation therapy (SBRT) and linear accelerator-based SBRT for lung tumors by comparison to provide a theoretical basis for the selection of treatment strategies.Methods:Seven patients who underwent SBRT for lung tumors in the Cancer Center of Affiliated Zhongshan Hospital of Dalian University from January 2022 to May 2023 were enrolled. Plans of gamma knife SBRT (γ_SBRT) or linear accelerator-based SBRT plans (X_SBRT) were designed for the 13 lesions in the patients, with adjacent lesions in the same patient sharing one plan. As a result, 10 γ_SBRT plans and 10 X_SBRT plans were obtained. All lesions received 30-50 Gy of radiation in 5-10 fractions. Then, dosimetric parameters were analyzed and compared between γ_SBRT and X_SBRT plans, including the target coverage, gradient index (GI), conformity index (CI), maximum dose ( Dmax); mean dose ( Dmean), and minimum dose ( Dmin) of planning target volumes (PTVs); lung volumes receiving 20 Gy or more ( V20), 10 Gy or more ( V10), 5 Gy or more ( V5), 100% of the prescription dose ( V100%), and 50% of the prescription dose ( V50%); Dmean and the percentages of lung volume receiving doses of 20 Gy or more (Lung_ V20) and 5 Gy or more (Lung_ V5) of ipsilateral lung; Dmean and Lung_ V5 of contralateral lung; and Dmax values of the esophagus, spinal cord, and heart. Results:Compared to X_SBRT plans, γ_SBRT plans exhibited superior GI, V20, V10, V5, V50%, the Dmean, Lung_ V20, and Lung_ V5 of ipsilateral lung, the Dmean and Lung_ V5 of the contralateral lung, and the Dmax of esophageal and heart ( z = -2.81 to -1.99, P < 0.05), higher Dmax and Dmean of PTVs ( z = -2.80, -2.80, P < 0.05), and longer delivery time ( z=-2.70, P<0.05). Meanwhile, there was no significant difference in target coverage, CI, and Dmax of the spinal cord ( P > 0.05). Conclusions:Gamma knife SBRT plans can achieve sharper dose falloff outside target volumes than linear accelerator-based SBRT plans. Gamma knife radiosurgery is expected to reduce the radiation dose to low-dose areas around PTVs and normal lung tissue in SBRT for lung tumors. However, it significantly prolongs the delivery time.

OBJECTIVE：To analyze the mass spectrometry fragmentation regularity of bicyclol ，bifendate and schisandrin C ， and to identify the impurities of bicyclol raw material. METHODS ：UHPLC-ESI-Q-TOF-MS method was adopted. Using electrospray ionization source ，in positive ion mode ，the excimer ion and characteristic fragments of bicyclol ，bifendate and schisandrin C were analyzed by means of TOF-MS. According to the mass change of fragments ，the possible fragmentation pathways were speculated ，and the fragmentation regularity were analyzed and summarized. Bicyclol raw material sample was first separated by liquid chromatography to find the impurity peaks in it ，and then the impurity peaks were analyzed by mass spectrometer；the impurity identification was conducted by combining with the fragmentation regularity. RESULTS ：The 3 compounds all produced [M+H] + excimer ion in the positive ion mode. After collision-induced dissociation ，the C-O bond ，the simple rupture of the C-C bond and the ring-opening cleavage of the oxygen ring occurred ；with the loss of neutral fragments ， mainly CH 2O，supplemented by CO 2，CO and CHO ，the dissociation was concentrated in the middle and high quality regions. C-C and C-O bonds of 3 compounds were simply broken only in the branched chain structure and/or oxygen ring structure ，but the structure of the biphenyl parent nucleus remained unchanged. Among them ，the bicyclol contained a benzyl alcohol structure ，so under acidic mobile phase conditions ，it would exist stably in the form of [M+H －H2O]+. Because schisandrin C contained 8-membered ring structure，ring opening first occurred under collision voltage ，and then neutral fragment loss occurred. The secondary mass spectra of impurity in bicyclol raw material were consistent with the mass spectra fragmentation of secondary fragments of bifendate. CONCLUSIONS：The study summarized mass spectrometry fragmentation regularity of 3 schisandrin derivatives. The impurity in bicyclol raw material may be bifendate.