Implementation of Constant Dose Rate and Constant Angular Spacing Intensity-modulated Arc Therapy for Cervical Cancer by Using a Conventional Linear Accelerator

Background： Volumetric-modulated arc therapy （VMAT） can only be implemented on the new generation linacs such as the Varian Trilogy（R） and Elekta Synergy（R）.This prevents most existing linacs from delivering VMAT.The purpose of this study was to investigate the feasibility of using a conventional linear accelerator delivering constant dose rate and constant angular spacing intensity-modulated arc therapy （CDR-CAS-IMAT） for treating cervical cancer.Methods： Twenty patients with cervical cancer previously treated with intensity-modulated radiation therapy （IMRT） using Varian Clinical 23EX were retreated using CDR-CAS-IMAT.The planning target volume （PTV） was set as 50.4 Gy in 28 fractions.Plans were evaluated based on the ability to meet the dose volume histogram.The homogeneity index （HI）, target volume conformity index （CI）, the dose to organs at risk, radiation delivery time, and monitor units （MUs） were also compared.The paired t-test was used to analyze the two data sets.All statistical analyses were performed using SPSS 19.0 software.Results： Compared to the IMRT group, the CDR-CAS-IMAT group showed better PTV CI （0.85 ＆#177; 0.03 vs.0.81 ＆#177; 0.03, P =0.001）, clinical target volume CI （0.46 ＆#177; 0.05 vs.0.43 ＆#177; 0.05, P =0.001）, HI （0.09＆#177;0.02 vs.0.11 ＆#177; 0.02, P =0.005） and D95 （5196.33 ＆#177; 28.24 cGy vs.5162.63 ＆#177; 31.12 cGy, P =0.000）, and cord D2 （3743.8 ＆#177; 118.7 cGy vs.3806.2 ＆#177; 98.7 cGy, P =0.017） and rectum V40 （41.9 ＆#177; 6.1% vs.44.2 ＆#177; 4.8%, P =0.026）.Treatment time （422.7 ＆#177; 46.7 s vs.84.6 ＆#177; 7.8 s, P =0.000） and the total plan Mus （927.4 ＆#177; 79.1 vs.787.5 ＆#177; 78.5, P =0.000） decreased by a factor of 0.8 and 0.15, respectively.The IMRT group plans were superior to the CDR-CAS-IMAT group plans considering decreasing bladder V50 （17.4 ＆#177; 4.5% vs.16.6 ＆#177; 4.2%, P =0.049）, bowel V30 （39.6 ＆#177; 6.5% vs.36.6 ＆#177; 7.5%, P =0.008）, and low-dose irradiation volume;there were no significant differences in other statistical indexes.Conclusions： Patients with cervical cancer treated with CDR-CAS-IMAT using Varian Clinical 23EX can get equivalent or superior dose distribution compared to those treated with IMRT.CDR-CAS-IMAT has a less treatment time and MU, which can reduce the uncertainty factor and patient discomfort in treatment.

Nitrogen addition overrides the effects of Stellera chamaejasme litter on the growth of Leymus chinensis and its associated mycorrhizal fungi

Rapid spread and growth of plants that are poisonous to animals produce large amounts of plant litter in degraded grasslands.Nitrogen(N)input may promote the growth of these poisonous plants and alter the rhizosphere microbes and arbuscular mycorrhizal fungi(AMF)in particular.However,it is unclear how poisonous plant litter affects the growth of palatable plants and their associated AMF in the rhizosphere and whether and how N deposition may mediate these effects.A greenhouse experiment was performed to test the combined effects of litter addition of a poisonous plant,Stellera chamaejasme,and N addition on the growth of a dominant grass,Leymus chinensis,AMF characteristics and soil properties.Litter addition significantly increased the ramet number and aboveground biomass of L.chinensis and soil available phosphorus(AP)concentration and decreased the spore density of AMF.However,the interaction of both treatments had no significant effects on traits of L.chinensis and AMF properties.Stellera chamaejasme liter positively affected L.chinensis by increasing AP and negatively affected AMF by combining balanced changes in soil nutrients and litter-induced allelopathic compositions.High N addition may alleviate soil N limitation and inhibit litter decomposition,thus overriding the litter's effects on L.chinensis and AMF.These findings imply that it is necessary to objectively and comprehensively evaluate the ecological functions of poisonous plants beyond their harmful effects on livestock.Simultaneously,N deposition should be an indispensable factor in predicting the relationships between poisonous plants and edible plants indegraded grasslands.