Objective To investigate the dose distribution and radiation risk of Varian thoracic cone beam computed tomography (CBCT) with default parameters with reference to Monte Carlo simulation and International Commission on Radiological Protection (ICRP) report 110.Methods EGSnrc/BEAMnrc code was used to simulate the material, thickness, and geometry of the kV CBCT source (kVS) to establish the kVS model.A benchmarked MCSIM code was applied to calculate the dose distribution in the ICRP phantom after the scan with the standard thoracic parameters (110 kV, 20 mA, and 262 mAs), and the conversion coefficient of absolute dose was obtained in a spherical phantom following the TG-61 protocol.The results of Monte Carlo simulation were validated by PDD and Profile in a water phantom and the measurement of the absolute dose in the computed tomography dose index (CTDI) phantom and Alderson phantom.The models including BEIR VⅡ were used to evaluate the radiation risks.Results With reference to the criterion of 3%/1 mm, the uncertainties of PDD and Profile were less than 2%.The difference between the measured and calculated values was<2.9% in the CTDI phantom and ≤0.05 cGy in the Alderson phantom.In the ICRP110 phantom, the doses to the left lung, right lung, left breast, right breast, heart, thyroid, trachea, cancellous bone, and cortical bone were 1.28, 1.39, 1.74, 1.80, 1.46, 0.48, 0.88, 0.85, and 1.84 cGy, respectively.The relative risks of ischemic heart disease, breast cancer, lung cancer, thyroid cancer, and tracheal cancer in a standard scan were1.001 , 1.009, 1.019, 1.000, and 1.008, respectively. Conclusions The accumulated dose and long-term risks of CBCT during image-guided thoracic radiotherapy cannot be neglected and should be effectively controlled.

Objective To prepare and characterize docetaxel incorporated phosphatidylcholine -sodium desoxycholate mixed micelles (DOX EPC/SDC MMs).Methods Docetaxel mixed micelles (DOX MMs) were prepared using the co-precipitation method .An optimized formulation was obtained by single factor method , which was used to study the effect of several factors on water solubility of DOX in MMs, including EPC/total(EPC+SDC)concentration, total(EPC+SDC) concentration, the pH and ionic strength of the hydrated solution .Then, the obtained DOX MMs were characterized by investigating particle size distribution and morphology , and by conducting dilute experiments to examin micelle stability . Results The EPC/total ( EPC+SDC) concentration ratio was 0.4.The total supplementary material concentration was 2.5%.Pure water was used to disperse the film .The drug loaded MMs had an average size of 18.56 nm and average zeta potential of -24.3 mV.A roundlike shape was observed under a transmission electron microscope ( TEM).Conclusion DOX EPC/SDC MMs, prepared by a simple and convenient method , can enhance water solubility , is physically compatible with injection solutions and is expected to become a new drug delivery system .

Objective Knowledge?based radiotherapy ( KBRT ) can reduce the plan quality variability induced by different experiences between physicians and improve the quality of treatment plans. Methods The Varian Rapid Plan system was used to train a dose?volume histogram ( DVH) prediction model. The obtained model was preliminarily applied to semi?automatic design of the preoperative treatment plans for rectal cancer. Eighty high?quality volumetric modulated arc therapy plans were imported into the model training set of the Rapid Plan system. The structures of the plans were matched to the corresponding labels and codes as listed in the library. The training started after the verification of prescription. The residual plots,regression curves,geometric plots for organ at risk ( OAR) ,in?field DVH plots,and model training logs were examined. After removal of the mismatch, the original plans were assessed to rule out outliers and influential data points. More similar plans may be added for another round of training. Ten KBRT plans were designed using the final model and compared with the clinical plans. Results For the two major OARs,the femoral head and bladder,the average goodness of fit of the principal component were 0?999 415/1.0 and 0?999 963/1.0 for the DVH model,and 0?999 651/1.0 and 0?999 945/1.0 for geometry?based expected dose model,respectively. In all the plans, 11 had Cook ’ s distance values exceeding the tolerance and 4 had studentized residual values exceeding the tolerance. The outliers were all kept in the training set to generalize the scope of the model. The 10 KBRT plans had significantly improved homogeneity indices for PGTV and PTV than the original plans (P=0?00,0?04).The 10 KBRT plans also had significantly reduced D50% to the femoral head and bladder as well as significantly reduced mean doses to the bladder than the original plans (P=0?042,0?000,0?005). Conclusions In this study,the Rapid Plan system is used to train a KBRT model for design of preoperative radiotherapy plans for rectal cancer. The results of preliminary application meet the clinical requirements.

Objective To investigate the value of echocardiography for assessing the right ventricular function before and af ter treatment in the patients with pulmonary embolism.Methods Ninety-six patients with pulmonary embolism in our hospital from June 2014 to December 2015 were selected as the research subjects and divided into low-risk group,intermediate-risk group and high-risk group according to the disease severity.The echocardiographic examination was performed before and after treatment in all cases.Results The pulmonary artery systolic pressure after treatment in the low-risk group was lower than that before treatment (P＜0.05).The transverse diameter of right ventricle,transverse diameter of right ventricle and pulmonary artery systolic pressure after treatment in the intermediate-risk group and high-risk group were lower than those before treatment (P＜0.05).The Tei index after treatment in the low-risk group,intermediate-risk group and high-risk group was lower than that before treatment (P＜ 0.05).The right ventricle ejection fraction (RVEF),right ventricular end-systolic volume (RVESV) and right ventricular end-dias tolic volume (RVEDV) in the low-risk group had no statistically significant difference between before and after treatment.RVEF after treatment in the intermediate-risk group and high-risk group was higher than that before treatment(P＜0.05),while RVESV and RVEDV after treatment were lower than those before treatment (P＜0.05).Conclusion Echocardiography can objectively re flect the change situation of right heart function before and after treatment in the patients with pulmonary embolism,and can be used as an evaluation method for the effect of pulmonary embolism treatment.

Objective To investigate the role of large-diameter magnetic resonance imaging (MRI) simulation in target volume delineation in radiotherapy for nasopharyngeal carcinoma (NPC).Methods Eighteen patients with NPC underwent computed tomography (CT) simulation and MRI simulation scans and localization in the same body position,with SOMATOM Sensation Open 40-row 82-cm large-diameter CT simulator and Siemens 3T MRI MAGNETOM Skyra 70-cm large-diameter simulator,respectively.The gross tumor volume (GTV) and parotid glands were delineated on all images according to the ICRU Report 50/62,and MRI was applied to observe the changes in GTV and parotid volume during radiotherapy.Paired t-test was applied to analyze the differences between GTVCT and GTVMRI and between GTVnx-CT and GTVnx-MRI.Results GTVMRI decreased significantly compared with GTVCT,and the average volume decreased from (213.64±84.59) cm3 to (199.68±84.69) cm3(p=0.006).As for the volume of primary lesions in the nasopharynx,GTVnx-MRI was significantly smaller than GTVnx-CT,and the volume decreased from (95.75± 24.76) cm3 to (88.12±26.25) cm3 (P =0.001);as for the volume of cervical lymph nodes,GTVnd-MRI was significantly smaller than GTVnd-CT,and the volume decreased from (117.89± 72.69) cm3 to (111.56± 70.69) cm3 (P=0.018).The targets delineated by CT and MRI did not overlap completely,with major differences in skull base bone and cervical soft tissue.The volume of both parotid glands delineated on MRI image was higher than that delineated on CT image,with a major difference in the deep lobe.MRI showed that GTV was reduced by 82.64± 16.87％ during radiotherapy,and the volumes of the left and right parotid glands were reduced by (32.7± 23.95) ％ and (34.7± 21.72) ％,respectively.Conclusions The delineation of target volume based on MRI simulation is more accurate than that based on CT simulation and can achieve a smaller volume range,which helps to guide target volume delineation in radiotherapy for NPC accurately.

Objective To explore the Monte Carlo calculation methods for the absolute dose calibration and output factor of 6 MV flattening-filter ( FF) and flattening-filter free ( FFF) photon beams based on TrueBeam accelerator .Methods The BEAMnrc code was used to model the LINAC head of FF and FFF modes.The BEAM_up covers the components from the target to the monitor chamber , and BEAM_down includes the structures beneath the chamber , the dose deposit to the monitor chamber contributed by the incidence electrons and scattered particles from the secondary collimators were calculated respectively .The incidence electron-induced dose at certain depths on the central axis were simulated by means of the DOSXYZnrc code .By means of dose calibration equation , the calibration factor for the standard field (10 cm ×10 cm) and the output factors for various fields (1 cm ×1 cm-40 cm ×40 cm) were computed respectively .Results For the 6 MV FF and FFF beams under the standard 10 cm ×10 cm field, 1 MU equals to 7.747 ×1013 ±3.099 ×1011 and 3.248 ×1013 ±1.624 ×1011 electrons to the target , respectively , which deposited 21.53 and 35.01 cGy to the monitor chamber of the virtual accelerator respectively .The difference between the simulated and calculated output factors were 0.72%±1.4%and 0.56%±0.78%for FF and FFF , respectively .Conclusions The model generated and measured output factors agree well , indicating the good accuracy of the dose calculation by the model , which would provides basis for further clinical dosimetric studies .

Objective To evaluate the feasibility and dosimetric features of a volume modulated arc therapy (VMAT)-configured model in knowledge-based optimization of fixed-field dynamic intensitymodulated radiotherapy (IMRT) plans based on the Varian RapidPlan system.Methods ① A dose-volume histogram prediction model was trained with 81 qualified preoperative VMAT plans for rectal cancer and then statistically verified.② For clinically approved 10 IMRT plans with the same dose prescription,the above model was used to automatically generate new optimization parameters and dynamic muhileaf collimator (MLC) sequences with field geometry and beam energy unchanged.③ In order to rule out the disparities between different versions,a single algorithm was used to calculate the absolute doses of the original and new plans.④ Statistical analyses were performed on dosimetric parameters after comparable target dose coverage was achieved in the two plans by appropriate normalization.Results On the basis of similar target dose homogeneity and coverage,RapidPlan significantly reduced the doses to the urinary bladder (D50％ by 9.01 Gy,P =0.000;Dmean by 8.08 Gy,P =0.005) and the femoral head (D50％ by 4.20 Gy,P =0.000;Dmean by 3.84 Gy,P=0.005) but significantly elevated the mean total number of monitor units (1211±99 vs.771±79,P=0.000) and the number of fields with multiple MLC carriage groups.The knowledge-based semi-automated optimization caused a significantly larger number of high-dose hotspots but a similar D2％ (52.54 vs.52.71 Gy,P=0.239).Conclusions The VMAT model can be used for the knowledge-based semi-automated optimization of IMRT plans to enhance the efficiency and OAR protection.However,the resulting high-dose hotspots need further manual intervention.

rt.

Objective To compare the performances of four commercially available LINAC daily QA instruments.Methods The dosimetric stability of a LINAC including central axis output,flatness and symmetry were verified and fine-tuned using a 3-dimensional water phantom,dosimeters and ionization chambers.The baseline of the four instruments including LINA-C,QUICK-C,BEAM-C and QA3 were set thereafter.Daily measurements of LINAC were conducted with these instruments respectively and the results were compared.Arbitrary errors (CAX and SYM) beyond TG-142 tolerances were introduced to the LINAC to test the sensibilities of each instrument in detecting these changes.Results Relative to the baseline that were measured by the 3-dimensional water phantom and dosimeters,the results monitored by the four instruments were comparable.The maximum disparities of the CAX,FLAT,and SYM were 0.5％ (LINA-C),-0.45％ (QUICK-C),and 0.5％ (BEAM-C),respectively.All checkers detected the known errors successfully.Conclusions The stabilities of all the four evaluated instruments met the requirements of daily QA for LINAC.LINA-C verifies CAX only.QUICKE-C,BEAM-C and QA3 can be used to perform all the daily QA protocols as suggested by AAPM TG 142 report.They also provide unique additional functions.The setup of baseline determines if the morning checkers could measure the LINAC dosimetric parameters correctly.When an error is alarmed by the morning checker,it is recommended to verify the performance of the instrument first rather than recalibrating the LINAC immediately.

Objective To explore the clinical effects of different dose of clopidogrel on the neural functions in patients with ischemic stroke.Methods 120 patients with ischemic stroke were randomly divided into low dose group (clopidogrel 75 mg daily) or high dose group (clopidogrel 150 mg daily).All the patients received the same basic treatment plus clopidogrel for 3 month.Both groups were evaluated and compared for their NIHSS scores, platelet count, platelet aggregation rate, neurologic deterioration rate, recurrence rate of cerebral infarction and intracranial bleeding rate at the time of admission, one month and three month.Results Compared to the scores at the time of admission, NIHSS scores decreased in both groups after one month treatment with statistical significance (P<0.05).The high dose group dropped more obviously.The NIHSS scores at 3 month in the low dose group had no difference statistically compared to 1 month (P>0.05), while high dose group declined significantly (P<0.05).The platelet count and platelet aggregation were decreased significantly in high dose group at 3 month(P<0.05), while there was no significant change in the low dose group(P>0.05).The neurologic deterioration rate, recurrence rate of cerebral infarction in the low dose group were 11.7％, 10.0％ respectively, significantly higher than that of high dose group (5.0％, 5.0％, respectively), which was statistically significant (P<0.05).However, there was no statistically significant difference (P>0.05) between two groups in intracranial bleeding rate (5.0％ and 6.7％ respectively).Conclusion Patients on clopidogrel 150 mg exhibited much better recovery of neural functions and greater reduction in the recurrence of cerebral infarction and atherosclerosis related cardiovascular events.