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DOSIMETRY COMMISSIONING OF THE LNS-INFN

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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DOSIMETRY COMMISSIONING OF THE LNS-INFN

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  1. 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.

  2. 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. INFN-LNS

  3. PTW MARKUSPLANE-PARALLER ION CHAMBER IN WATER PHANTOM INFN-LNS

  4. 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 INFN-LNS ^ taken from BJR Supplement 25 (1996)

  5. THE NEW SCANDITRONIX Si-DIODE IN PROTON BEAMS (Proton Field waterproof Detector-narrow beamno.DZA192 1001) INFN-LNS

  6. 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

  7. 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 INFN-LNS

  8. MODULATED PROTON DEPTH DOSES FOR EYE THERAPY 15 MM SOBP vs RANGE SHIFTER INFN-LNS

  9. 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 ] INFN-LNS

  10. 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 INFN-LNS

  11. He-Ne Scanning LaserDensitomiter PMMA Phantom

  12. INFN - LNS

  13. INFN-LNS 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

  14. 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 INFN-LNS

  15. 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 INFN-LNS

  16. DOSE MONITORING SISTEM TRANSMISSION ION CHAMBER INFN - LNS

  17. 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 INFN-LNS

  18. 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

  19. 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% INFN-LNS

  20. 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%

  21. INFN-LNS DOSIMETRY INTERCOMPARISON AT PSI (FULLY MODULATED BEAM)

  22. 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 INFN-LNS

  23. 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 INFN-LNS

  24. PATIENT DOSES (STRAY RADIATION) (PERSONAL MONITORING, TWO PATIENTS TESTED) INFN-LNS 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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