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INFN-LNS. DOSIMETRY COMMISSIONING OF THE LNS-INFN. PROTON THERAPY FACILITY THE DOSIMETRIC CHARACTERISTICS OF NARROW PROTON BEAMS USED IN EYE THERAPY HAVE BEEN DEFINED BY USING DIFFERENT RADIATION DETECTORS  IONIZATION CHAMBERS ( parallel-plate, mini thimble chambers ) SILICON DIODES

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INFN-LNS

DOSIMETRY COMMISSIONING OF THE LNS-INFN

PROTON THERAPY FACILITY

THE DOSIMETRIC CHARACTERISTICS OF NARROW PROTON BEAMS USED IN EYETHERAPY HAVE BEEN DEFINED BY USING DIFFERENT RADIATION DETECTORS

IONIZATION CHAMBERS (parallel-plate,minithimble chambers)

SILICON DIODES

RADIOCHROMIC AND RADIOGHRAPHIC FILMS

THERMOLUMINESCENCE DETECTORS

1)CENTRAL AXIS DEPTH-DOSE DISTRIBUTIONS

2)LATERAL (TRANSVERSE) PROFILES

3)OUTPUT FACTORS (FSDF)

TO PROVIDE INPUT TO THE TPSAND FOR M.U. CALCULATIONS.

QUALITY CONTROL PROCEDURES

DOSIMETRIC COMMISSIONING OF 60 MeV PROTON BEAMS

PRODUCED AT LNS FOR EYE THERAPY

SHAPED WITH 5 - 30 mm CIRCULAR BRASS COLLIMATORS.


  • PROTON DEPTH-DOSE DISTRIBUTIONS

  • THE PTW MARKUS PLANE-PARALLEL ION CHAMBER WAS USED IN THE COMMISSIONING AS THE REFERENCE DETECTOR FOR DEPTH-DOSE MEASUREMENT IN PROTON BEAMS (ICRU 59, IAEA 398)

  • THE DESIGN OF THE MARKUS CHAMBER

  • 1)Active volume=0.05 cm3, 2) Electrode separation=2 mm, 3) Collector diameter=5.4 mm

  • 4)tentrance window=2.3 mg/cm2 5) Exact Location of peff.

  • PROVIDES DEPTH-DOSE DISTRIBUTIONS

  • WITH HIGH SPATIAL RESOLUTION AND HIGH PRECISION

  • ) PMMA CUP IS PROVIDED TO SEAL THE CHAMBER FOR USE IN WATER

  • )A SPACER IS PROVIDED FOR USE IN A SOLID PHANTOM, WHICH ALSO SERVES AS A HOLDER FOR A RADIOACTIVE SOURCE FOR STABILITY CHECKS.

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PTW MARKUSPLANE-PARALLER ION CHAMBER IN WATER PHANTOM

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CENTRE

MAXIMUM RANGE

(mm)

EQUIVALENT ENERGY

(MeV)

PEAKPLATEAU RATIO

F.W.H.M.

(mm)

Distal-dose falloff

d90%-10%

(mm)

CATANA

30.60

60.2

4.68

3.29

0.81

CCO^

31.0

60.4

4.85

3.65

0.80

PSI^

30.0

60.0

4.47

1.10

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^ taken from BJR Supplement 25 (1996)


THE NEW SCANDITRONIX Si-DIODE IN PROTON BEAMS

(Proton Field waterproof Detector-narrow beamno.DZA192 1001)

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DETECTOR

PEAK

DEPTH

(mm)

PEAK-PLATEAU RATIO

F.W.H.M

(mm)

Distal-dose falloff (1)

d90%-10%

(mm)

Distal-dose falloff (2)

d80%-20%

(mm

PRACTICAL RANGE

(d10%, ICRU 59)

THE NEW SCANDITRONIX Si-DIODE IN PROTON BEAMS

(Proton Field waterproof Detector-narrow beamno.DZA192 1001)

MARKUS PTW

30.14

4.68

3.19

0.71

0.50

31.15

DIODE

SCANDITRONIX

30.07

4.89

3.07

0.80

0.60

31.06

CYLINDRICAL MINIDIODE SPECIFICATIONS

Detector Material: Hi-pSi, high doped p-type silicon (preirradiated for use in proton beams).

Detector diameter: 0.6 mm (t = 60 m)

INFN-LNS


Modulated proton depth doses for eye therapy
MODULATED PROTON DEPTH DOSES FOR EYE THERAPY

MODULATION

(SOBP)

(mm eye tissue)

DISTAL-DOSE FALLOFF (1)

d90%-10%

(mm eye-tissue)

DISTAL-DOSE FALLOFF (2)

d80%-20%

(mm eye tissue)

MAXIMUM

DOSE

IN SOBP 

%

BEAM RANGE

(90% DISTAL)

(mm eye-tissue)

MODULATOR

RANGE SHIFTER

MOD: 000/00

RS: 14 mm

14.5

0.91

0.65

101.6

14.38

MOD: 010/02

RS: 10 mm

10.5

0.90

0.60

104

18.27

MOD: 009/02

RS: 1.8 mm

20.30

0.80

0.55

103.9

27.04

CCO

 17

0.90

0.75

< 102

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MODULATED PROTON DEPTH DOSES FOR EYE THERAPY

15 MM SOBP vs RANGE SHIFTER

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BEFORE EACH TREATMENT PERIOD

TREATMENT DEPTH DOSE PROFILES HAVE TO BE VERIFIED.

TO VERIFY RANGE MODULATION AND MAXIMUM RANGE OF THE BEAM

DEPTH-DOSE MEASUREMENT WHEEL (CCO DIODE SCANNER)

WHEEL IS COMPUTER CONTROLLED, AND RELATIVE DOSE MEASURED

AS RATIO BETWEEN WHEEL’S DETECTOR AND REFERENCE DETECTOR

TOLERANCES

1)  [(MEASURED RANGE) / (REQUIRED RANGE)]:  0.2 mm

2)  [(MEASURED MODULATION) / (REQUIRED MODULATION)]: [ -0.1 mm // +0.9 mm ]

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LATERAL OFF-AXIS BEAM PROFILES  

1) LATERAL PENUMBRA: d80%-20%

2) Field ratio:

3) L95%

4)SIMMETRY (AREA RATIO):

5) FLATNESS:

MD-55-2 RADIOCHROMIC FILMS WERE USED IN COMMISSIONING

tissue equivalence – dose rate indipendence

Linear dose response – high spatial resolution

ONLY ONE CALIBRATION FILE IS NEEDED TO EVALUATE

FILMS EXPOSED AT DIFFERENT DEPTHS

Energy indipendence

1.3 mm

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He-Ne Scanning LaserDensitomiter

PMMA Phantom



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KODAK XV FILMS AND SCANDITRONIX DIODE WERE USED IN COMMISSIONING

IF CALIBRATION FILES PRODUCED FOR KODAK XV FILMS

AT DEPTH OF SOBP ARE USED FOR TRANSVERSE BEAM MEASUREMENTS

GAF MD55-2 = KODAK XV FILM


BEFORE EACH TREATMENT

PROTON BEAM PROFILES AT ISOCENTRE ARE TO BE CHECKED

IN AIR X-Y DIODE SCANNING COMPUTER CONTROLLED DEVICE

PLANNED TOLERANCES

1) LATERAL PENUMBRA (d80%-20%)1.50 mm 2) BEAM SIMMETRY (Sr )3%

3)BEAM FLATNESS: Rt%3%4) FIELD RATIO: H0.90

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DOSE MONITORING SYSTEM (IN-BEAM DOSE MONITORS)

THE PROTON DOSE IS MONITORED BY TWO INDEPENDENT TRANSMISSION UNSEALED ION CHAMBERS, PLACED IMMEDIATELY UPSTREAM OF THE PROTON NOZZLE.

TRANSMISSION CHAMBERS HAVE SEPARATE CABLING, BIAS SUPPLIES (800 V) AND CURRENT INTEGRATORS AND ARE ARRANGED AS A REDUNDANT COMBINATIONTO TERMINATE THE BEAM.

TRANSMISSION ION CHAMBERS ARE CALIBRATED DAILY AGAINST A REFERENCE PARALLEL-PLATE MARKUS ION CHAMBER, LOCATED AT THE ISOCENTRE.

COMMISSIONING TESTS

1)PRECISION

1a)SHORT TERM PRECISION: (CV) OF THE RATIO ROF DOSE MONITOR UNITS TO DOSIMETER SCALE READING FOR n=5 CONSECUTIVE IRRADIATIONS OF 15 Gy.

MEASURED CV = 0.1%

1b) LONG TERM PRECISION (WEEKLY STABILITY):

MEASURED [(cGy/U.M.)WEEK]:1.5%.

2)LINEARITY

THE RATIO V BETWEEN THE MEASURED PROTON DOSE AND DOSE MONITOR UNITS SHALL BE WITHIN  1% AT ALL MONITOR SCALE READINGS, i.e. IN THE CLINICAL RANGE UP TO 15–20 Gy.

MEASURED RATIO

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DOSE MONITORING SISTEM

TRANSMISSION ION CHAMBER

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DOSE RATE MONITORING (BEAM INTENSITY MONITOR)

 THE PROTON BEAM RATE IS MONITORED BY THE VOLTAGE SIGNAL (VSF) PROVIDED BY THE FIRST SCATTERING FOIL, LOCATED IN VACUUM IMMEDIATELY UPSTREAM OF THE EXIT WINDOW.

IBEAM(nA) = 0.0412 + 6.0835  VSF (R2=0.9999)

(VSF) IS USED BY THE C.S.TO STOP THE BEAM IF THE RATE XCEEDS A PRESET LIMIT.

NORMAL TREATMENT BEAM CURRENT  4 nA CLINICAL DOSE RATE =1220 Gy/min.

U.M. =K

Alarm current

Zmarkus = 1 mm Full energy beam

Normal current

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ABSOLUTE DOSIMETRY (BEAM CALIBRATION, cGy/U.M.)

 FOR REFERENCE DOSIMETRY, AT LNS, A PLANE-PARALLEL MARKUS ION CHAMBER IS USED IN A WATER PHANTOM, BY EXTENDING TO PROTON BEAMS THE FORMALISM OF THE IAEA 381 CODE OF PRACTICE ON THE USE OF PLANE-PARALLEL ION CHAMBERS IN HIGH ENERGY ELECTRON DOSIMETRY.

cGy

( TAB. 7.1 ICRU 59) (Wair/e)cp = 1.031 (ICRU 59)

cGy/nC

(nC)

(sw,air)q

pQ = 1.00 (ICRU 59, IAEA TRS-398, MED.PHYS. 1995 :22)

FOR DOSE CALIBRATIONS OF INDIVIDUAL PATIENTS, THE CALIBRATION IS MADE IN A UNIFORM DOSE REGION AT THE MIDDLE OF SOBP, AT ISOCENTRE, WITH THE 25 mm DIAMETER REFERENCE COLLIMATOR ON BEAM DELIVERY NOZZLE.

FOR DAILY DOSE CHECKS, A PMMA PHANTOM BLOCK IS USED:

A RADIOACTIVE CHECK DEVICE (90Sr) IS USED FOR OPERATIONAL AND CONSTANCYCHECKS OF DOSIMETRY SYSTEM (1%, NCRP).

INFN-LNS


AN EXRADIN T1 THIMBLE ION CHAMBER [A-150 TE, 0.05 cm3, NK(60Co)]

CAN BE USED AT LNS IN THE WATER PHANTOM, ACCORDING TO ICRU 59 

BECAUSE OF THE Cavity length AND Outer diameter of the chamber,

USE IS LIMITED TO (  )  15 mm AND (SOBP WIDTH)  12 mm.

WORK IN PROGRESS

NOW AVAILABLE BY PTW ND,w,60CoFOR T1 EXRADIN AND MARKUS LNS CHAMBERS

ADOPTION OF IAEA TRS-398 CODE OF PRACTICE

Dw,Q = MQ ND,w,Q0 kQ,Q0

ESTIMATED UNCERTAINTY OF Dw,QUNDER REFERENCE CONDITIONS (1 S.D.)

ICRU 59 (Nk=1%) IAEA TRS-398 (ND,w,Q0 =1%)

EXRADIN T1 2.6% 2.1%

PTW MARKUS 3.1% 2.5%

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INFN-LNS

PROTON DOSIMETRY INTERCOMPARISON (ECHED, ICRU 59)

BEFORE STARTING LNS PROTON THERAPY FACILITY

) INTERCOMPARISON (1) AT CCO (PHYSICA MEDICA, VOL.XV, N.3)

LNS (PTW MARKUS, T1-EXRADIN) CCO (A-150 FW-IC18,REFERENCE DOSE)

(Dw) [(PTW MARKUS) / (FW-IC18)]: 1%

(Dw) [(T1-exradin) / (FW-IC18)]: 1.4%

) INTERCOMPARISON (2) AT PSI (PHYSICA MEDICA VOL.XVII, S.3, PTCOG XXX 1999)

1) CCO (FW-IC18, MARKUS) 2) LNS (MARKUS, EXRADIN-T1, PTW PMMA FARMER)

3) PSI (PTW GRAPHITE FARMER, MARKUS) 4) TERA ( MARKUS, EXRADIN-T1)

% = 1.2% max (%) = 3.5%


INFN-LNS

DOSIMETRY INTERCOMPARISON AT PSI

(FULLY MODULATED BEAM)


OUTPUT FACTORS (FSDF)

) AT THE INITIAL CALIBRATION OF CYCLOTRON THE OUTPUT DOSE RATE HAS BEEN MEASURED FOR ALL COLLIMATORS AREA ENCOUNTERD IN THE CLINICAL PRACTICE.

) TO EVALUATE IF THERE ARE SIGNIFICANT DROPS OF DOSE PER MONITORUNIT WHEN COLLIMATOR DIAMETER DECREASES TO A FEW MILLIMETERS.

) THE MOST RELIABLE RELATIVE OUTPUT VALUES ARE PROVIDED FROM RADIOCHROMIC DETECTORS, ESPECIALLY FOR NARROWEST BEAMS (VATNITSKY).

NO SIGNIFICANT DECREASE OF BEAM OUTPUT (cGy/U.M.)

FOR COLLIMATOR DIAMETER UP TO 5 mm

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OUTPUT FACTORS (FSDF)

) FROM EXPERIMENTAL RESULTS WE CAN STATE THE LOWER BOUND OF COLLIMATOR DIAMETER FOR WHICH FRELATIVE OUTPUT IS MEASURED ACCURATELY WITH EACH DETECTOR

1)MARKUS CHAMBER CAN BE USED IN PROTON BEAMS WITH 12 mm

2)TLDs AND SCANDITRONIX DIODE CAN BE USED UP TO =8 mm

IN CLINICAL PRACTICE AT LNS

GAF-DETECTOR IS USED FOR EVALUATION OF OUTPUT FACTOR

FOR SHAPED NARROWEST BEAMS

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PATIENT DOSES (STRAY RADIATION)

(PERSONAL MONITORING, TWO PATIENTS TESTED)

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A)TWO PERSONAL BADGE-DOSIMETERS WERE PLACED ON THE CHEST OF PATIENTS DURING THE WHOLE PROTON TREATMENT.

1) ENEA FILM BADGE PERSONAL DOSIMETER (, , x)0.05 mSv

2) NRPB PADC NEUTRON PERSONAL DOSEMETER 0.20 mSv

PATIENTS COMPLETING TREATMENT INDUCED DOSE RATE

 15 Sv/h

(10’)

 1.5 Sv/h


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