Electron linear accelerator for radiotherapy

ChuanxiangTang/HaoZha

TsinghuaUniversity,Beijing100084,China

AtAFAD2018(9thAsianForumforAcceleratorsandDetectors),January28-31,2018,DaejeonConventionCenter,Daejeon,Korea

Jan. 28/Sunday

17:00 – 20:00 Registration and Reception (DCC 201)

Jan. 29/Mon. Jan. 30/Tue. Jan. 31/Wed.

Morning Opening & Plenary Working Group Excursion

(09:00 – 18:00) Afternoon Working Group

(Banquet) Plenary & Closing

(Lab Tour)

Registration Counter & Information Desk

Jan. 28 17:00 –20:00 DCC 201

Jan. 29 08:30 –17:00 DCC 1F

Jan. 30 08:30 –17:00 DCC 1F

Conference Venue Plenary session: DCC Conference hall, Room 301 Parallel session: DCC 1F WG1: Room 101, WG2: Room 102, WG3: Room 103, WG4: Room 104 WG5: Room 105, WG6: Room 106, WG7: Room 107

AFAD2018

Outline

•  Briefoverviewofradiotherapy

•  Recentdevelopmentsinmedicalelectronlinearaccelerator

•  ActivitiesinTsinghuaUniversity

Cancer worldwide

Cancer

8.8M

Heartdisease

8.76M

Stroke

6.24M

Top3causesofdeathworldwide,2015(DatafromWHO)

2000

10M

2012

14M

2025

19M

Annualcancerincidentworldwide(DatafromWHO)

•  Cancerhasbeenthefirstkillertohumanbeings;

•  Incidenceofcancerisrisingrapidly.

Radiotherapy

Factsaboutradiotherapy(Datafromhigh-incomecountries,2012,IAEA) Patientsneedradiotherapy

60%

5%

Costofradiotherapy/Costinallcancertreatments

18%

Patientscuredbyradiotherapy(5-year-survival)

Total5-year-survivalrate(45%)

•  Surgery,chemotherapyandradiotherapyarestillthemostlyusedtreatmentsofcancer.

•  Radiotherapy(radiationtherapy)hasahighcost-effectivenessratio.

How does radiotherapy kill the tumor cell?

X-rayIonizing

O-(OH)Freeradicals

DNADNArepair

Damage

Succeed

Failed Death

biologychanged

Trigimmuneresponses

HowdoesX-raykillthetumorcell?

Unabletoreproduce

•  RadiotherapyuseionizingradiationtobreaktheDNAoftumorcells(alsoharmsthenormaltissue,whichisthesideeffect).

•  Usually,atumorcellshaslessabilitytorepairitsDNAandthusiseasiertobekilled.

History of X-ray radiotherapy

•  X-raywasusedtotreatthecancelpatientin1896.•  AfterWW-II,hazardsofionizingradiationweremoreclearlyunderstood.Manytechnologiesweredevelopedtoreducetheradiationdoseonnormaltissues.

1895…1950196019701980199020002010X-raydiscovery LINAC IGRT&SBRT

MLC CBCT

PicfromWikipedia

IMRT&VMATCRT

CT&MRI

Electron LINAC in radiotherapy

•  ElectronLINACswerefirstusedinradiotherapysince1950s.

•  NowmostmachinesuseElectronLINACsastheX-raysources.

•  6MVisthemost-oftenchoiceoftheLINACvoltage.

High-energy(e.g.14MV)machine:Duetothediameterlimitation,LINACshouldbeplacedhorizontally.Andamagnetisusedtobendthebeam.

Low-energymachine:LINACisshortandcanbeverticallyplaced.

Outline

•  Briefoverviewofradiotherapy

•  Recentdevelopmentsinmedicalelectronlinearaccelerator

•  ActivitiesinTsinghuaUniversity

Recent developments •  Spatialresolution(inpositioningthetumor)isacrucialfactorinradiotherapy.

•  Higherresolutioncanbring:•  Lesssideeffect,increasesthequalityoflife;•  Abletodeliverhigherdose,increasesthecurerate.

PTVwithoutimage-guided

PTVwithImage-guided

Tumor

Uncertaintyofthetumorposition

PTV:planningtargetvolume Dp(DimensionofPTV)=Dt(Dimensionoftumor)+5xσ(Spatialresolution,RMS)Ifthesizeofatumor=3cm: σ Dp Volumeof

PTV/tumor 0.5mm 3.25cm 127% 1mm 3.5cm 159% 2mm 4cm 237%

IGRT: Image-guided radiotherapy

•  Sub-millimeteraccuracyisgoingtobeneededinradiotherapy.

•  IGRT:twofunctions(imaging,treatment)inonesystem/machine.

Schemeofimaging Precision

Ultra-sound >5mm

Externalmarker(Optical) >2mm

Internalmarker(Magnetical) >1mm

Fluoroscopy Unknown

CTonrail 1mm

PET Unknown

KVX-ray/CBCT 1-2mm

MRI <2mm

Coaxial2DX-ray <2mm

Candeterminepositionandvolumeofthetargetbeforedeliveringthedose(OfflineIGRT)

Cantrackpositionandvolumeofthetargetduringthedosedelivery(Online/real-timeIGRT)

KV X-ray imaging

•  Imagingsystemonthegantry.RotateforCTimaging(Cone-BeamCT).

•  Higherresolution;•  Largeextradose(ofimaging);

•  Longertime;

Linactube

KV-Xraysource

Imagingboard

Variantruebeam

•  Imagingsystemnotonthegantry.Twoorthogonalimagingdevices:

•  Lowerresolution;•  Fastandlessdose;•  Realtimetracking;

PicfromStonybrookcancercenter

Coaxial imaging (Dual energy LINAC)

•  IfImagingsystemandLINACtubeareindifferentcoordinatesystem→Needtransformation→Systematicerror(~1mm).

•  IfLINACcandotheimagingwork,thesystematicerrorcouldbeeliminated.

•  However,MVimaginghaspoorquality.

•  KV/MVdualenergytubeisunder-developing.

KVimaging MVimaging

Patient

LINAC

Imagingboard Patient

LINAC

Highenergyfortreatment

Lowenergyforimaging

http://dx.doi.org/10.1155/2014/705604

MRI+LINAC •  MRIcouldyieldhighqualityimagingonsofttissueandwithnoextradose.

•  MRI+LINACsystemisnowunder-developing.

•  Difficulties:•  EffectofstrongalternatingB-fieldonthelinactube;•  ImagingtimeofMRIisquitelong;

•  … ElektaMRI+LINAC RoboticMRI+LINAC(StanfordUniv.)

SBRT: Stereotactic body radiotherapy.

•  Radiotherapytreatmentisdividedintomanyfractions:•  letthenormaltissuehavetimetorecover(repairDNA);

•  Reducetheriskonnormaltissueduetoerrorinpositioning.

•  HighresolutionIGRThasasignificantlylessdoseonnormaltissue→allowhigherdoseperfraction(lessfractions)→SBRT.

2Gy 2Gy 2Gy 2Gy

2Gy 2Gy 2Gy 2Gy

…

2Gy 2Gy 2Gy 2Gy

Conventional:60Gy=2Gyx30days

15Gy 15Gy 15Gy 15Gy

SBRT:60Gy=15Gyx4days

Improvetreatmenteffectontumorcells

Lesstreatmenttime

Moreeffective

Higher dose rate

•  SBRTneedlargedoseperfraction→increasingthedoserateoftheLINAC:

•  Higherpowersource(magnetron)/OptimizingonRFstructure;

• Workonflat-filter-free(FFF)mode→2timeshigheron-axialdose→TPS(dose-planningsystem)ismorecomplex.

E2VMG7095magnetronPeakpower:3.1MW

Flexible LINAC

•  Ifpatientreceiveradiotherapyfrommoredirections,themaximumdoseonnormaltissueisreduced(lesssideeffect).

•  C-band/X-bandLINAChaslessweight→moreflexibleframe→providemoredirection.

•  lessweightofLINAC→higheraccuracyinpositioning.VeroSBRT:C-band CyberknifeRoboticRT:X-band

Outline

•  Briefoverviewofradiotherapy

•  Recentdevelopmentsinmedicalelectronlinearaccelerator

•  ActivitiesinTsinghuaUniversity

History in Tsinghua accelerator lab

• WebuiltfirstmedicalLINACinChina:BJ10(in1970s)

History in Tsinghua accelerator lab

1974

1977

1987

1993

1998

2003

2006

2009

2012

2016

2018

ü  Convened a research group of more than 40 institutes to develop the first

medical electron linac in China;

ü  BJ-10 travelling wave linac(10 MeV electron)

ü  4 MeV axis-coupling linac

ü  14 MeV linac

ü  Multi-energy linac (6~20 MeV)

ü  Dual-beam linac (X-ray/electron)

ü  Dual beam energy linac (kV/MV)

ü  Electron standing wave linac for IMRT

ü  C-band 6 MeV linac (1000 rad/min, 40 cm)

ü  High dose rate 6 MeV linac（1400 rad/min）

ü  X-band 6MeV linac (expected: 800 rad/min)

kV/MV coaxial LINAC

• Wefabricatedaprototypelinactubein2007andsuccessfullydemonstratedtheenergyswitching(6MVto600kV).However,therearestillsomechallenges:

•  Doserateisnothigh(about800cGy/min@1meter)

•  Linactubeisworkingnotstablyatlowenergystate(600kV)Fullradiotherapymachineprototype(developedbyNUCTECH.Inc,China) kV/MVLinactube

S-band large dose-rate LINAC

•  AfullmoduleofX-raysource:magnetron+waveguide+linactube(withshielding),weight=500kg.

•  Mechanicallyadaptedformanykindofradiotherapymachines;

•  Controlitlikeastepmotor:trig→trytodeliveradoseunit(1MU)→feedbacktherealdose;

•  Pinsarereservedtoalignedthelinactube(bytwistingthem).

Pinsforalignment

C-band medical LINAC

• WedesignedandtestedaC-band6MeVLINACin2013.

•  Thedoserateispromising(1000cGy/min@1m).

Frequency 5712MHz Power 2.1MW Peakbeamcurrent 130mA Doserate(at1mwithdutycycleis0.1%)

1000cGy/min

Captureratio 32.8% SpectrumFWHM 0.1MeV(1.5%) RMSspotsize 1.4mm AcceleratingCellnumber. 13cells

Acc.structurelength 29cm Shuntimpedance 130MΩ/m

ParameterofC-bandmedicallinacdesign C-bandmedicallinactubeTotallength:40cmWeightofthetube:7kg

https://journals.aps.org/prab/pdf/10.1103/PhysRevSTAB.16.090102

C-band medical LINAC

•  TheLINACinstalledatitaniumwindowatitsend.Sothatwecanmeasureparametersoftheoutputelectronbeam:

•  Spotsize:lessthan1.5mmJ

•  SpectrumFWHM:0.4MeVL(expected0.1MeV,mayduetojitterinthepowersource)

1mm

Spectrumvspower

X-band medical LINAC

•  X-bandmedicalLINACiscompactbuthaslowerdoserate.

• WearedevelopingahighdoserateX-bandlinac•  40cmstructurelength

•  800cGy/min@1meter

X-band

S-band

C-band

S-band X-band

1250 kg

450 kg

Total weight of Linac

TypicaloutputpowerofX-band(9300MHz)magnetrons

Cyberknife

X-band medical LINAC

•  WedevelopedanX-bandtubeintheyear2000(olddesign).ThenewX-bandtubewillimproved:

•  Morepowerfulsource(expect1.7–1.8MW)

•  Increasetheshuntimpedance

•  Increasethecaptureratio(lesspowerabsorbedbyun-capturedbeam)

•  Optimizethebeamspectrum.

Olddesign

Improvepowersource

Optimization

Olddesign:Inputpower=1.2MWDoserate=300cGy/min@1m

Thanks