ABSTRACT
Objective To establish an accurate simulation model for proton scanning beam using Monte Carlo (MC) code.Methods The MC model of proton scanning beam treatment nozzle was established by using MC code FLUKA combined with the geometric structure of the treatment nozzle in Shanghai Proton and Heavy Ion Center (SPHIC).The MC beam model was established through the simulation of the integrated depth dose distribution (IDD) in water and the lateral profile in air at the isocenter points.The model was used to simulate the depth and lateral dose profile of Spread Out Bragg Peak (SOBP) of proton beam.The calucated result were compared with TPS calculation values.Results For the distal R90,the deviations of simulation and measurement at all energies were less than 0.5 mm.For distal fall off (R80-20),the deviations between simulation and measurement at each energy were within 0.1 mm.The biggest difference between measurement and simulation of the proton beam spot size was within 0.45 mm.The result of simulation and TPS calculation of proton SOBP matched well,with the γ index pass rate being higher than 90％ (Criteria:2 mm,2％).Conclusions The MC code FLUKA can be used to model the nozzle of scanning proton beam,which can meet the clinical requirements and accurately simulate the proton beam transport in material.After construction and verification on the basis of measurement,this model can be used as a dose verification tool to evaluate clinical proton treatment plans,in order to reduce the beam time for dose verification and thus increase the number of patient treatment in proton therapy.
ABSTRACT
Objective To investigate the dosimetric advantages of proton and heavy ion radiotherapy ( particle radiotherapy) for liver cancer adjacent to gastrointestinal tract. Methods Ten patients with liver cancer adjacent to gastrointestinal tract receiving radiotherapy were recruited in this study. The prescription was first given with 50 Gy ( RBE )/25 fractions to planning target volume 1 ( PTV-1 ) using proton irradiation,and then administered with 15 Gy ( RBE)/5 fractions to PTV-2 using carbon-ion irradiation. A simultaneous integrated boost regime was established using the same variables and prescription. The organ at risk ( OAR) constraints were referred to RTOG 1201. All plans were performed for dose evaluation after qualifying the OAR constraints. Results The dose coverage of 95％ of the prescribed dose ( V95) for PTV-1 from the photon plan (97.15％±4. 27％),slightly better than (96.25±6. 69％) from the particle plan (P=0. 049).The V95 of PTV-2 from the particle plan was (94.6％±6. 22％),comparable to (95.12％±3. 49％) from the photon plan (P=0. 277).The integral dose of Body-PTV-1 delivered by the particle plan was merely 39. 9％ of that delivered by the photon plan. The mean liver-GTV dose from the particle plan was only 81. 8％ of that from the photon plan. The low-dose irradiation to the stomach and duodenum from the particle plan was significantly lower than that from the photon plan. Conclusions The dose to the liver-gross tumor volume ( GTV) is the main factor limiting the increase of total dose to the tumors. When the absolute GTV in the liver is relatively large,particle radiotherapy can maintain comparable dose coverage to the tumors as the photon radiotherapy whereas significantly reduce the dose to the liver-GTV.
ABSTRACT
Objective To construct expression vectors of calmodulin(CaM)mutants N2 and C2,and to express,purify,and identify the mutant proteins,in order to study the interactions between CaM and calcium channels. Methods The cDNA of N?lobe and C?lobe of CaM were used to prepare the cDNA of N2 and C2. Next,the recombinant cDNAs were cloned into a pGEX?6p?3 plasmid,and the recombinant plasmids were trans?ferred into E.coli BL21 cells. The transfected BL21 cells were stimulated with IPTG. The fusion proteins were extracted by ultrasonication and puri?fied by using GS?4B beads. Finally,protein activity was identified by the pull?down assay. Results Both the restriction digestion map and the DNA sequence identification results confirmed that the recombinant plasmids were successfully constructed. SDS?PAGE results showed high purity and concentration of N2 and C2 proteins. Their activities and binding abilities with the calcium channel fragment were confirmed by the pull?down assay.Conclusion In this study,expression vectors of N2 and C2 are successfully constructed,and physiologically active N2 and C2 CaM mutant proteins are obtained.