The significant advantage of proton therapy over other particle-based techniques is in the unique physical characteristics of the Bragg peak.It can achieve a highly conformal dose distribution and maximize the probability of tumor control by varying the irradiation energy.Most proton facilities use cyclotrons for fixed energy beam extraction and are equipped with degrader and collimator systems for energy modulation and emittance suppression.However,interactions between charged particles and degrader materials inevitably cause beam loss and diver-gence and deteriorate beam performance,which present great challenges for downstream transport and clinical treatment.In this work,we investigate a method of energy reduction by combining boron carbide and graphite in a degrader to obtain greater beam transmission at lower energy.The results demonstrate that the beam size and emittance at the exit of the combined degrader diverge less than those of multi-wedge one in the energy range of 70-160 MeV.Correspondingly,the transmission effi-ciency after the first dipole also shows improvements of 36.26％at 70 MeV and 70.55％at 110 MeV.As a com-ponent with a high activity level,the degrader causes additional ambient radiation during operation.Residual induced radiation even remains several hours after system shutdown.Analysis of material activation and induced radiation based on 1 h irradiation with a 400 nA beam current shows that the combined degrader has a definite advantage in shielding despite producing more secondary particles.Both radioactivity and average ambient dose equivalent are reduced by 50％compared with the multi-wedge degrader at the important cooling time of 1 h.After 12 h and 24 h of cooling,the radiation levels of degraders decrease slightly due to the presence of long half-life residual nuclides.The average dose generated from the multi-wedge degrader is still 1.25 times higher than that of the combined one.

Man-Fen Han;Jin-Xing Zheng;Xian-Hu Zeng;Jun-Song Shen

Hefei Institutes of Physical Science,Chinese Academy of Sciences,Hefei 230031,China;University of Science and Technology of China,Hefei 230026,China

核技术（英文版）

[1]Man-Fen Han;Jin-Xing Zheng;Xian-Hu Zeng;Jun-Song Shen-.Investigation of combined degrader for proton facility based on BDSIM/FLUKA Monte Carlo methods)[J].核技术（英文版）,2022(02):30-39

degrader,BDSIM,cyclotrons,degraders

Investigation,combined,proton,facility,FLUKA,Monte,Carlo,methods,significant,advantage,therapy,over,other,techniques,unique,physical,characteristics,Bragg,peak,It,achieve,highly,conformal,dose,distribution,maximize,probability,tumor,control,by,varying,irradiation,energy,Most,facilities,fixed,beam,extraction,equipped,collimator,systems,modulation,emittance,suppression,However,interactions,between,charged,particles,materials,inevitably,loss,gence,deteriorate,performance,which,present,challenges,downstream,transport,clinical,treatment,this,work,investigate,reduction,combining,boron,carbide,graphite,obtain,greater,transmission,lower,results,demonstrate,that,size,exit,diverge,less,than,those,multi,wedge,range,MeV,Correspondingly,effi,ciency,after,first,dipole,also,shows,improvements,ponent,causes,additional,ambient,during,operation,Residual,induced,even,remains,several,hours,shutdown,Analysis,activation,nA,current,has,definite,shielding,despite,producing,more,secondary,Both,radioactivity,average,equivalent,reduced,compared,important,cooling,After,levels,decrease,slightly,due,presence,long,half,life,residual,nuclides,generated,from,still,times,higher

0.549993