Dose Delivery System

Dose Delivery System

Study and development of theDose Delivery System for theNational Center of OncologicalHadrontherapy (CNAO)Simona GiordanengoTorino January 12 2009

OverviewIntroduction Advanced Radiotherapy and Hadrontherapy Dose delivery systems Active scanning system CNAO projectMy research activity CNAO Dose Delivery System (Hardware andSoftware characteristics) Preliminary test of the CNAO scanningperformanceConclusions2

Standard and advancedRadiotherapyLINAC6 – 18 MVMaximum dose rate:~ 5 Gy/min[Gy] = [J/Kg]Dynamic Multi-LeafCollimator (DMLC)3D conformal Radiotherapy (3DCRT)To increase conformityIntensity Modulated Radiotherapy (IMRT)HadrontherapyTo increase conformity andbiological effects3

HadrontherapyTumors treatment with heavy particlesStandardRadiotherapyHigh dE/dxHigh IonizationHigh Dose (Gy = J/Kg )Inelastic collision withnuclei: neutrons productionand others fragmentsDepth dose distribution of various radiation modalities44

Ions vs X-rays physical advantagesMultipleScattering‣ Low dose on surface‣ High dose in depth‣ High precision on dose delivery‣ Minimal lateral scatteringThese are mainly dependent on the Dose Delivery System5

The hadrontherapy “machine”The elements and devices necessary to conform,control and adjust the beam just before thepatient belong to the Dose Delivery System (DDS)ACCELERATORBeam lineDose DeliveryPatientMagnets (dipoles and quadrupoles), vacuum chambersand beam diagnostic devices characterize the beamtransport system just before the Dose Delivery6

From the original beam dimension to thetarget dimension through the Dose DeliverySystemVacuum chamberPencil BeamFWHM 2 ÷ 10 mmTargetDim 1 ÷ 30 cmTwo main methods have been successfully adopted tocover a large transversal area with a small nativepencil beam: THE PASSIVE and the ACTIVE METHODS7

Dose Delivery elements for aPASSIVE SCATTERING system• 1 st transversal beamspread• 1 st energy modulation(Spread Out Bragg Peak)• 2 nd energy modulation toincrease homogeneity• 1 st (X,Y) conformation• Energy (Z) conformation• 2 nd (X,Y) conformation8

ACTIVE BEAM DELIVERY SOLUTIONSTwo dipole magnets smear out the particles of a beam pulseF = q * (v Λ B)XYVacuumwindowyTargetθzBeamxLScanning magnetsLBeammonitorsOnly beam monitors between vacuum window and patient to increaseefficiency and reduce unnecessary dose reduce scattering and nuclear interactions between particles andmaterial along the beam path9

To obtain the desired field, several scanning techniques can be adoptedRASTER SCAN SOLUTIONThe beam is moved continuously in a pre-selected pattern over thetarget area and a well-defined number of particles are delivered ineach line element.Protons,Carbon ionsyScanningmagnetsScannedFieldzxIsocenter10

SPOT SCAN SOLUTIONSIt moves a beam spot across the field in discrete stepsProtons,Carbon ionsyScanningmagnetsScannedFieldzxRequirements: fast system toswitch on-off the beamIsocenterVery time consuming11

VOXEL SCAN SOLUTIONSThe beam is aimed to a voxel for the time necessary to reach theprescribed fluence then it is steered to the next voxel withoutstopping the particle deliveryProtons,Carbon ionsyScanningmagnetsScannedFieldzxIsocenter12

CNAO “3D” active dose delivery system• (X,Y) VOXEL SCANNINGLinac2 sources• (Z) PARTICLE ENERGY VARIATIONthrough the acceleratorSynchrotronScanningmagnetsSLICESE 0

Detectors characteristics2 integral chambers2 strip chambers 1 pixel chamberIntensity MeasurementRead every 1 μsIntegral sensitive areaGap 5mmGas nitrogenHV 400 VPosition Measurementevery 80-100 μsprecision 100 μm# strips 128(1.65 mm pitch)Gap 5mmGas nitrogenHV 400 V2D Position Measurement2D Intensity MeasurementPrecision 200 μm# pixels 1024(6.6 mm pitch)Gap 5mmGas nitrogenHV 400 V14

CNAOCentro Nazionale di Adroterapia OncologicaTo treat deep tumours (range 1-30 cm): p (E : 60-250 MeV, I :10 10 ), C 6 +(E : 120-400 MeV/u, I : 4*10 8 ) Gaussian Beam : 4 10 mm (FWHM) Active Dose Delivery System Beam position step: 1 ± 0.1 mm Maximum field: 20 x 20 cm 2 Patient daily fraction in ~ 2 -3 minSynchrotron~26 m3 treatment rooms:3 horizontal lines1 vertical lineTreatment rooms1515

Power plantSynchrotron vaultHospital roomsMain entranceCNAO - Pavia16

Synchrotron room17

CNAO Dose Delivery System Hardware and Software characteristics18

Based on NI products and LabVIEW Real-Time Operating SystemBOX 1 BOX 2DATA(monitor)Control RoomTreatmentPlanning SystemDose Delivery InterfacesChopper/DumpTiming SystemSupervision SystemScanning MagnetsCrate PXI -NIInterlock System19

CRATE PXIPXI trig busExternal BUS to connect FPGA1-2-3-4, interlockmodule and chopper modulePXI data busCPUTTOI/O I/O65341FPGA16534FPGA2 265343FPGA365344FPGA4I/OMasterTimingControlRoomInterlockChopperIM1IM2StXStYPXExternal BUS to trasnfer databetween FPGA 2-3-4MagnetsX Y20

E n21


“TREATMENT LOADING”The sequential beampositions for each voxel arepreventively stored in amemory and are translatedin a set of strip coordinatesand magnet currentsFor each voxel:(E n , Np, X, Y)yE 0E 1Enx“START DAQ”“SPILL ON”“END of SLICE or SPILL”“STOP DAQ”“DATA STORAGE”(counts, x strip , y strip , I x , I y )zSlice EndedNOFor the ionization chamber counts alsoPressure and Temperature dosimetriccorrection is done for each patientYESTreat EndedYESNOAfter a trigger from Timing Systemthe monitor data acquisition fromFPGA starts“LOGFILE CREATE”WAIT NEXT TREATMENT23

IN REAL-TIME when SPILL is ON foreach voxel FPGA1 counts particles, FPGA2 checks the beam position andcompares it with the expected one FPGA4 corrects the currents set ifnecessary (feed-back operations).“TREATMENT LOADING”“START DAQ”“SPILL ON”“END of SLICE or SPILL”VOXEL END FPGA1 sends a trigger to the othersFPGAs which prepare themselves for thenext voxel. FPGA4 transmits the new voxelcurrents to the magnet PS.Treatedvoxels“STOP DAQ”“DATA STORAGE”Slice EndedYESTreat EndedYES“LOGFILE CREATE”NONOSliceE nWAIT NEXT TREATMENT24

“TREATMENT LOADING”“START DAQ”SLICE and SPILL END DD stop the Beam and DAQ DD rady to start new DAQTREATMENT END DD creates “logfiles” andsend to the SS DD ready for nexttreatment“SPILL ON”“END of SLICE or SPILL”“STOP DAQ”“DATA STORAGE”Slice EndedYESTreat EndedYES“LOGFILE CREATE”NONOWAIT NEXT TREATMENT25

Preliminary test of the CNAOscanning performance26

THE AIMS OF THE MEASUREMENTS Acceptance test of the communicationbetween Dose Delivery and Power Supply The time response of the scanning magnetfield The performance of the scanning systemwith a real treatment27

SCANNING CHARACTERISTICSPower SupplyScanning MagnetDesigned and built in collaborationbetween OCEM S.p.A and INFN-CNAOBPower rated = ±550A/±660VRate 100 kA/s v beam > 20 m/sCurrent precision = ± 100 ppmM. Incurvati et al “FAST HIGH-POWER POWER SUPPLY FORSCANNING MAGNETS OF CNAO MEDICAL ACCELERATOR” –EPAC 08 - GenovaL = 4.4 mH, R = 26 mΩB max = 0.3 T with 606 AHomogeneity better than 0.2 %28

Setup for the magnetic fieldmeasurementV out x50PXIFPGA7831-RI in = 100mAFPGA with ADCanalog channels: 8resolution :16 bitInput signal range:±10 VDAQ rate:200 kHzNoise : 3 counts (~0.17 A from PS)High Linearity Hall Probe for Room andCryogenic TemperaturesNominal control current, , In : 100 mASensitivity : 439 mV/TRange for B :± 3 TLinearity : < 0.2 %Active area:0.5x1.25 mm 2Band width:~6 MHz29

DATA FLOW4 Mbaud optical linkPXI with FPGADose Delivery SystemI ref, err40 kHzI ref, I meas, err200 kHzB (a.u.)PXI with FPGAPower Supply10 m Shielded cableHall probeMagnet30

Acceptance test of the communicationbetween Dose Delivery and Power Supply Set of different currents(-540 AA540 A) Transmission times check4 Mbaud40 kHz of data Simulation of a transmission error Detection of current out of rangeOKOKOKOK31

Performance Tests• Scan from -540 A +540 A -540 A with thefollowing current steps:– 1 A, 2 A, 5 A, 10 A, 15 A, 20 A, 540 A– Δt = 2 ms, 4 ms and 10 ms (= time between two steps)Probe Hall in 3 different positions within the magnet (0 cm, +20cm, +25 cm)• Slices from treatments (scanin X and scan in Y) withΔt proportional to the fluence32

Scanning parameters Position –Speed –Time –Intensity –DoseBeam at position A:X Acoordinate A plannedI Acurrent for PSN A# particles in A (Dose)t Atime to deliver N AAV A-BBBeam at position B:X Bcoordinate B plannedI Bcurrent for PSN B# particles in B (Dose)t Btime to deliver N Bt A-B = step timeI A-B= current stepBeam Speed = V A-B = (X A -X B )/t A-BPower Supply Current rate = dI/dt= (I A -I B )/t A-BI DDI PStStep planned by DoseDelivery from plannedcoordinatePS current Stept33

Scan with 10 A stepevery 2 msI_DD (A) Current set by the DoseDelivery.Acquisition rate 40 kHz.I_PS (A) Current read by thePower Supply control loop.Acquisition rate 40 kHz.B (a.u.) Hall probe measurementin arbitrary unit to normalize thefield to the current.Acquisition rate 200 kHz.AV A-BB34

Linearity step 10AB-IddIps-IddHysteresisPower Supply non-linearity negligible35

Scanning speed measurementsGENERAL REQUIREMENTS:if 2.5 A ≤ΔI ≤ 15 A ΔI/ Δt > 100 kA/secif ΔI < 2.5A time < 200 μsBeam Speed for 1 A stepFrom linear fit between 10 %- 90 %ΔI/Δt = 0.0201 A/μsΔI/Δt = 20 kA/sec1 A in Δt~ 50 μs

2 A step in the magnetcenterFrom linear fit between 10 %- 90 %Slope = 0.0314 A/μsΔI/Δt = 31 kA/sec2A in Δt< 70 μs2 A step at the magnet edgeFrom linear fit between 10 %- 90 %ΔI/Δt = 0.0291 A/μsΔI/Δt = 29 kA/sec2A in Δt< 70 μs70 μs

10 A step in the magnet centerTime Time for 20%-80% A step ( for ΔI = 6A) = 35 ± 5 usΔI/Δt = ~ (6/35)*10 6 ~ 170 kA/sec170 kA/sec >> 100 kA/sec10 A step in the magnet edgerequired10 A step out of the magnet38

Slice from Real Patient TreatmentMEASURED and PLANNED VOXELS POSITIONS39

N particles/voxelSlice dose distributionsMEASUREDPLANNEDMaximum N particles/voxel ~ 4*10 4Treatment MEDIUM , slice 940

Relative maximum difference0.008Difference between thereal distribution obtainedusing the measured beampositions and the idealdistribution (from TPS)better than 1 %.(Required 2.5 %)41

S. Giordaengo et al.“Performance test of the scanning system for CNAO,Italian National Center of Oncological Hadrontherapy”Soon ready to be submitted forpubblication to NIM42

CONCLUSIONS about my activity‣ The CNAO Dose Delivery operations defined‣ The DD data acquisition developed‣ A software prototype to interface the DD with several CNAOsubsystems implemented and will be ready to start the DD debug soon‣ The interface with the Supervision System successfully tested‣ The interface with the Power Supply for scanning magnets defined,developed and successfully tested‣ Performance test of the scanning system successfully doneFUTURE‣ Master Timing interface test‣ Interlock System interface test‣ DD debug at CNAO with beam‣ Overall software optimizations43

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